Foreword

QCVN 12:2014/BXD was compiled by the Institute of Construction Science and Technology with the support of experts from the International Copper Association Southeast Asia, the Department of Science, Technology and Environment, and was appraised by the Ministry of Science and Technology, and promulgated by the Ministry of Construction in accordance with Circular No. 20/2014/TT-BXD of the Minister of Construction dated December 29, 2014.

1. GENERAL PROVISIONS

1.1 Scope

This Regulation prescribes the mandatory technical requirements to be complied with in the design, new construction, renovation, and repair of electrical installations of dwelling and public buildings.

NOTE: The highest voltage level mentioned in this Regulation does not exceed 1,000 V, 50 Hz frequency.

1.2 Subjects of application

This Regulation applies to organizations and individuals involved in the design and construction of electrical installations of dwelling and public buildings.

1.3 Referenced documents

The following referenced standards are essential for the application of this Regulation. In case the referenced documents are amended or supplemented, the latest version shall be applied.

TCVN 9888-1:2013 (IEC 62305-1:2010) Protection against lightning – Part 1: General principles;

TCVN 9888-3:2013 (IEC 62305-3:2010) Protection against lightning – Part 3: Physical damage to structures and life hazard;

TCVN 7447-7-710:2006 (IEC 60364-7-710:2002) Electrical installations of buildings – Part 7-710: Requirements for special installations or locations – Medical locations.

1.4 Terms and definitions

For the purposes of this Regulation, the following terms and definitions apply:

1.4.1

Electrical installations of dwelling and public buildings (hereinafter referred to as building electrical installations)

The combination of electrical conductors, electrical equipment, earthing systems, and protective conductors from the supply point of the building to the points of consumption.

1.4.2

Wiring system

The combination of conductors, busbars, cables and their fixing, holding, connecting, protective and enclosing accessories (conduits, boxes).

1.4.3

Wiring installation

The combination of wiring systems.

1.4.4

Circuit

The combination of conductors and electrical equipment supplied from the same origin and protected against overcurrent by the same protective device or group of devices.

1.4.5

Insulated conductor (hereinafter referred to as conductor)

A metallic conductor core enclosed in an insulating sheath.

1.4.6

Current-carrying conductor

A conductor for carrying electrical energy, including phase conductors and neutral conductors. In this Regulation, the metallic core of current-carrying conductors shall be made of copper.

1.4.7

Protective conductor (hereinafter referred to as PE conductor)

A conductor connecting the metallic enclosures of electrical equipment and accessories to the earthing terminal at the location where the electrical equipment is installed or to the earthed neutral point of the power supply source.

1.4.8

Electric cable (hereinafter referred to as cable)

A combination of:

a) One or more conductors;

b) Individual protective sheath for each conductor (if any);

c) Common protective sheath (if any);

d) Common armor for the entire cable (if any);

e) Outer sheath.

1.4.9

Busbar

A metal bar used for conducting electricity.

1.4.10

Conduit

A tube made of material with appropriate mechanical strength, used for running conductors and cables.

1.4.11

Trunking

An accessory having the same function as a conduit, but with a rectangular cross-section and a cover.

1.4.12

Main distribution board

A board containing electrical distribution devices installed at the beginning of the supply line to the building.

1.4.13

Sub-distribution board

A board containing electrical distribution devices installed after the main distribution board to supply electricity to a part of the building.

1.4.14

Control device

A device used to perform actions on electrical equipment to achieve certain purposes.

1.4.15

Circuit breaker (hereinafter referred to as breaker)

A connecting device capable of closing, opening, and withstanding load current during normal operation and short-circuit current.

1.4.16

Earth electrode

A conductive part placed directly in the earth or in a conductive medium in contact with the earth.

1.4.17

Switching device

A device used for closing or opening an electrical circuit.

1.4.18

Protection against electric shock

Measures to ensure safety for humans depending on the current intensity and duration of current passing through the human body. Protection against electric shock includes the following types:

a) Basic protection: Protection against electric shock when the equipment has no insulation faults;

b) Fault protection: Protection against electric shock when the equipment has insulation faults;

c) Additional protection: Supplementary to basic protection and fault protection.

1.4.19

Safety service

Power supply to maintain the operation of certain essential equipment to protect human life in case of danger.

1.4.20

Isolating switch

A connecting device which, in the open position, provides a safe isolating distance. An isolating switch does not close or open load current but can withstand load current for an extended period and short-circuit current for a short period as specified.

1.4.21

Load switch

A connecting device capable of closing, opening, and withstanding load current. A load switch can close onto a short circuit and withstand short-circuit current for a short period as specified, but cannot open short-circuit current.

1.4.22

Residual current

The algebraic sum of the instantaneous values of currents flowing in all current-carrying conductors at a given point in an electrical circuit. When the equipment is operating normally, the residual current is equal to the sum of the leakage currents. When there is an insulation fault, the residual current is equal to the fault current plus the leakage currents.

1.4.23

Leakage current

Current that flows to earth or through conductive parts external to the equipment to earth during normal operation of electrical equipment.

1.4.24

Residual current device (hereinafter referred to as RCD)

A protective device that disconnects a circuit when the residual current increases to a certain value.

1.4.25

Direct contact

Contact of a person with a live part while that part is operating normally.

1.4.26

Arm’s reach volume

The volume of space above, around, and below a surface on which a person is standing or walking that can be reached by hand, without holding any tools. The limits of the arm’s reach volume are shown in Appendix A.

1.4.27

Indirect contact

Contact of a person with the metallic enclosure of equipment when the insulation between the live part and the metallic enclosure is faulty.

1.4.28

Metallic enclosure of equipment

The outer metallic part of the equipment, which is conductive and accessible. Normally, this enclosure is not live, but when the insulation is faulty, it becomes live.

1.4.29

Busbar

A large cross-section conductor bar.

1.4.30

Collecting bar

A busbar to which multiple separate circuits can be connected.

1.4.31

Extra-low voltage (hereinafter referred to as ELV)

An alternating voltage not exceeding 50 V.

1.4.32

Separated extra-low voltage (hereinafter referred to as SELV)

ELV having a source, conductors, and electrical equipment not connected to other electrical circuits and not connected to earth.

1.4.33

Protective extra-low voltage (hereinafter referred to as PELV)

ELV with protective earthing.

1.5 Abbreviations

1.5.1 ELV (Extra-Low Voltage)

1.5.2 IP (Index Protection)

1.5.3 IT – a type of earthing system (see Appendix D).

1.5.4 LPS (Lightning Protection System)

1.5.5 N (Neutral)

1.5.6 PE (Protective Earthing)

1.5.7 PELV (Protective Extra-Low Voltage)

1.5.8 RCD (Residual Current Device)

1.5.9 SELV (Separated Extra-Low Voltage)

1.5.10 SPD (Surge Protection Device)

1.5.11 TN-S – a type of earthing system (see Appendix D).

1.5.12 TT – a type of earthing system (see Appendix D).

2. TECHNICAL PROVISIONS

2.1 Wiring systems and electrical equipment

2.1.1 General requirements

The installation methods and conditions related to wiring systems and electrical equipment shall meet the requirements to ensure the safety of the electrical system and users, and provide easy access for inspection, repair, and replacement.

2.1.2 Requirements for installation methods of wiring systems

2.1.2.1 Appropriate installation methods for wiring systems shall be applied to meet the current-carrying capacity requirements of conductors.

2.1.2.2 Single-core cables with steel wire or steel tape armor shall not be used for three-phase alternating current circuits. All current-carrying conductors and PE conductors of the same three-phase alternating current circuit placed in ferromagnetic conduits or boxes shall be run in the same conduit or box.

2.1.2.3 In case multiple circuits are run in a single conduit or box, all conductors shall have insulation corresponding to the highest rated voltage.

2.1.2.4 In case multiple circuits are run in a single multi-core cable, all conductors of the cable shall have insulation corresponding to the highest rated voltage.

2.1.2.5 Conductors of a circuit shall not be distributed in different multi-core cables, conduits, boxes, trays, or cable ladders; except for multi-core cables forming a circuit and installed in parallel containing one conductor of each phase and the neutral conductor (if any).

2.1.2.6 A common neutral conductor shall not be used for multiple main circuits, unless the phase conductors and neutral conductors are identifiable and there are devices to isolate all current-carrying conductors.

2.1.2.7 When multiple circuits are connected to a junction box, the conductor ends of each circuit shall have insulating partitions.

2.1.2.8 Flexible conductors shall be used to connect electrical equipment that may need to be temporarily moved. Flexible conduits shall be used to protect flexible conductors.

2.1.2.9 Unsheathed conductors shall be run in conduits or boxes.

2.1.3 Requirements for wiring systems according to external conditions

2.1.3.1 Necessary measures shall be taken to protect all parts of wiring systems against external influences.

2.1.3.2 Wiring systems shall be ensured to operate within the temperature range between the highest and lowest temperatures at the installation location and not exceed the limit temperature during normal operation and the limit temperature during fault conditions. Components of wiring systems shall only be installed and handled at temperatures within the limits specified by the manufacturer.

2.1.3.3 Wiring systems shall be shielded by insulating plates or placed away from heat sources or use components that can withstand the possible temperature increase or be locally reinforced with heat-resistant materials.

2.1.3.4 Wiring systems shall be ensured to have a degree of protection (specified in Appendix B) suitable for the installation location; not be damaged by condensation or water ingress; the protective sheath and insulating sheath of fixed installed cables shall remain intact and special measures shall be taken for cables installed underwater or frequently exposed to water.

2.1.3.5 The risk of solid foreign objects penetrating shall be minimized; measures shall be taken to prevent dust or other substances from accumulating in large quantities that reduce the heat dissipation capacity of wiring systems.

2.1.3.6 Protection against corrosion or the use of materials resistant to corrosive and polluting substances shall be provided for parts of wiring systems. Different metals that can cause electrolytic reactions shall not be allowed to come into contact with each other, unless special measures have been taken to avoid the consequences of such contact.

2.1.3.7 Fixed wiring systems shall be protected against mechanical damage. When connecting cables and conductors to electrical equipment, the degree of protection of the electrical equipment shall not be reduced.

2.1.3.8 Wiring systems shall be ensured to be supported or fixed to structures of equipment with vibration, especially vibrating equipment. Suspended electrical equipment (such as ceiling fans, chandelier) shall be connected using flexible conductors.

2.1.3.9 Measures shall be taken to avoid damaging cables, conductors, and cable ends; avoid mechanical impact on conductors and connections during installation, use, or maintenance; and protect buried wiring systems under floors; protect wiring systems against mechanical damage when cables, busbars, and conductors pass through expansion points or penetrate through partitions.

2.1.3.10 Lubricants containing silicone shall not be used for pulling conductors or cables on trays or ladders. Concealed conduits embedded in building structures shall be completely installed between accessible points before inserting conductors or cables, except for pre-wired conduit assemblies manufactured specifically for this purpose. The bending radius for pulling conductors and cables shall not cause damage to conductors and cables.

2.1.3.11 Conductors and cables shall be supported at appropriate distances so that conductors and cables are not damaged by their own weight or by the electrodynamic force of short-circuit currents (this force is only considered for single-core cables with cross-sectional areas larger than 50 mm²). Conductors or cables that can withstand the constant tension force due to their own weight shall be used when running vertically.

2.1.3.12 Wiring systems permanently embedded in walls shall run horizontally, vertically, or parallel to the edges of the walls. Cables and conduits buried underground shall be protected against mechanical damage or buried deep enough and marked.

2.1.3.13 Appropriate protective measures shall be taken in places where wiring systems are at risk of damage by plants or animals.

2.1.3.14 Measures shall be taken to protect wiring systems against the effects of solar radiation and ultraviolet radiation.

2.1.3.15 Wiring systems shall be designed and installed in accordance with the seismic requirements of the building.

2.1.3.16 Cable supports and protection systems that allow relative movement shall be used so that conductors and cables are not subjected to mechanical stress when the building structure is at risk of movement. Flexible wiring systems shall be used for flexible structures or structures expected to have movement.

2.1.4 Requirements for current-carrying capacity

2.1.4.1 The maximum current flowing in conductors of wiring systems under normal operating conditions for a long period shall comply with the manufacturer’s specifications for conductors.

2.1.4.2 The current-carrying capacity of conductors (or cables) in a group shall be determined based on the lowest permissible operating temperature limit of a conductor in the group of conductors (or cables) having different permissible operating temperature limits, together with the appropriate group derating factor.

2.1.4.3 The derating factor of conductors in a circuit shall be calculated according to the number of current-carrying conductors. In the case of three-phase circuits with balanced load current (when the total harmonic distortion of the 3rd harmonic or odd multiples of 3 does not exceed 15% of the fundamental frequency current amplitude), the neutral conductor of that circuit does not need to be considered.

2.1.4.4 Measures shall be taken to distribute the load current between conductors in accordance with the current-carrying capacity of conductors when two or more current-carrying conductors are connected in parallel, except when the conductors are made of the same material, have the same cross-sectional area, have approximately the same length, and have no branch circuits.

2.1.4.5 In case it is not possible to distribute the current or it is necessary to connect in parallel 4 or more conductors, the option of using busbars shall be considered.

2.1.4.6 The current-carrying capacity shall be determined according to the part of the wiring route with the most unfavorable heat dissipation conditions, except for the part of the conductor passing through walls with a length less than 0.35 m.

2.1.4.7 Both ends of the metallic sheaths and/or non-magnetic armor of single-core cables in the same circuit of the wiring route shall be connected. In case of cables with conductor cross-sectional areas larger than 50 mm² and non-conductive outer sheaths, the metallic sheaths and/or non-magnetic armor may be connected to each other at one point along the route, but the length of the cable from the connection point shall be limited according to the condition of safe voltage between the sheath or armor to earth, and the unconnected ends shall be insulated.

2.1.5 Requirements for cross-sectional areas of conductors

2.1.5.1 The cross-sectional area of phase conductors in alternating current circuits shall not be smaller than the following values:

– For lighting circuits: 1.5 mm²;

– For power and lighting circuits and circuits dedicated to power: 2.5 mm²;

– For signaling and control circuits: 0.5 mm²;

– For wiring from floor distribution boards to distribution boards of apartments or rooms: 4 mm²;

– For vertical risers supplying one or several floors: 6 mm².

2.1.5.2 Cross-sectional area of neutral conductors

a) The neutral conductor shall have a cross-sectional area at least equal to that of the phase conductor in the following cases:

– In single-phase 2-wire circuits;

– In three-phase circuits, the cross-sectional area of the phase conductor is less than or equal to 16 mm²;

– In three-phase circuits with 3rd harmonic and odd multiples of 3 and the distortion caused by these harmonics is from 15% to 33% of the amplitude of the fundamental frequency current;

b) In case the 3rd harmonic and odd multiples of 3 cause a distortion greater than 33%, the cross-sectional area of the neutral conductor shall be selected larger than the cross-sectional area of the phase conductor;

c) For three-phase circuits where the cross-sectional area of the phase conductor is greater than 16 mm², the cross-sectional area of the neutral conductor may be smaller than the cross-sectional area of the phase conductor if the following conditions are simultaneously met:

– The load of the circuit is balanced between phases and the 3rd harmonic and odd multiples of 3 do not exceed 15% of the amplitude of the fundamental frequency current. Under this condition, the cross-sectional area of the neutral conductor shall also not be less than 50% of the cross-sectional area of the phase conductor;

– The neutral conductor is protected against overcurrent;

– The cross-sectional area of the neutral conductor is not less than 16 mm².

2.1.6 Requirements for earthing systems

Building electrical systems shall not apply earthing systems other than those specified in Appendix D.

2.1.7 Requirements for voltage drop at point of utilization

The voltage drop between the starting point of the power supply and any electrical equipment in the building electrical system shall not exceed 5% of the rated voltage of the building electrical system.

2.1.8 Requirements for electrical connections

The connections between conductor cores and the connection points between conductor cores and equipment shall ensure continuous and long-lasting electrical conductivity, sufficient mechanical strength, be appropriately protected, and shall be accessible for inspection, testing, and maintenance, except for connections designed to be buried underground, filled with compounds, and connections between cold leads and heating elements, welded or crimped connections, connections that are part of electrical equipment, meeting the standards of that equipment.

2.1.9 Requirements for minimizing fire propagation for wiring systems

2.1.9.1 In case there is a requirement to minimize fire propagation, wiring systems shall use materials that minimize the risk of fire propagation; shall not reduce the fire safety performance of building structures. Types of cables without fire propagation resistance shall only be used to connect from fixed wiring systems to electrical equipment and shall not pass from one fire compartment to another. Parts of wiring systems not of the fire propagation resistant type shall have fire-resistant sheaths when used.

2.1.9.2 Gaps both inside and outside conduits and boxes, where wiring systems penetrate, shall be sealed with materials having the same fire resistance limit as the penetrated building component, except for non-combustible conduits and boxes with an internal cross-sectional area not greater than 710 mm², meeting the test requirements for IP33, and the ends of the conduits and boxes entering one of the penetrated compartments are separated by building structures. Sealing materials shall withstand external influences such as wiring systems and withstand the effects of water and the effects of fire products like building components.

2.1.10 Requirements for wiring systems running adjacent to other services

2.1.10.1 Low voltage and ELV circuits shall not be arranged on the same wiring route, unless:

a) All cables or conductors on the wiring route have insulation corresponding to the highest voltage;

b) All conductor cores in a multi-core cable have insulation corresponding to the highest voltage present in the cable;

c) The cable has insulation corresponding to its voltage and is placed in a separate compartment in conduits or trunking;

d) The cables are installed on trays with separate partitions;

e) Separate conduits or trunking are used.

2.1.10.2 When buried wiring systems intersect or run close to communication lines, the distance between these types of lines shall be ensured to be at least 100 mm or one of the following requirements shall be met:

a) Separation between the lines by fire-resistant bricks, concrete or using fire-resistant conduits;

b) Mechanical protection measures between the lines at intersections.

2.1.10.3 Wiring systems shall not be placed near other technical lines serving other purposes that may cause damage to the wiring systems, unless appropriately protected.

2.1.10.4 Wiring systems shall not be placed in lift shafts, unless they are part of the lift.

2.1.11 Requirements for installation of wiring systems related to maintenance and cleaning

2.1.11.1 The installation of wiring systems shall be in accordance with the maintenance and cleaning requirements throughout their life cycle.

2.1.11.2 When it is necessary to remove a protective measure for maintenance or cleaning, it shall be reinstalled to ensure that the original degree of protection is not reduced.

2.1.11.3 Safe access to parts of wiring systems requiring maintenance and cleaning shall be ensured.

2.1.12 Requirements for installation of distribution boards and protective devices

2.1.12.1 A main distribution board shall be installed at the entrance of the building, except for the case where a branch from an overhead line into the building already has a protective device with an operating current not exceeding 25 A installed.

2.1.12.2 Sub-distribution boards shall be installed after the main distribution board to supply power to parts of the building.

2.1.12.3 Control and protective devices shall be installed in distribution boards except for the case where protection has been provided at the starting point of the branch and when the distribution board is supplied by a separate line.

2.1.12.4 A control device shall be installed in the main distribution board of the supply line to public buildings or parts of public buildings.

2.1.12.5 Distribution boards shall be installed in dedicated electrical rooms or in locked wall recesses. In locations prone to flooding, distribution boards shall be installed higher than the highest possible flood level.

2.1.12.6 In case there is no dedicated room, distribution boards shall be installed in other rooms, dry basements, or in technical floors, if these locations are easily accessible to managers, or in separate rooms of the building with non-combustible walls with a fire resistance time of not less than 45 minutes.

2.1.12.7 When installing distribution boards outside a dedicated electrical room, the following requirements shall be met:

a) Installed in a dry, convenient, and easily accessible location for operation and repair;

b) Installed in boxes, cabinets, or wall recesses with protective doors.

2.1.12.8 Distribution boards shall not be installed under or in toilets, bathrooms, wash areas, laundry rooms, or rooms with chemicals.

2.1.12.9 Covers, valves, flanges, inspection doors, and taps of water pipes, ventilation ducts, steam pipes, and other types of technical boxes shall not be arranged in the location of distribution boards. Gas pipelines and pipelines carrying flammable substances shall not pass through the room where distribution boards are located.

2.1.12.10 Rooms dedicated for installing distribution boards shall be electrically ventilated and illuminated; shall have doors that open outwards and are lockable.

2.1.13 Requirements for installation of electrical equipment in buildings

2.1.13.1 Electrical equipment installed in buildings shall be suitable for the voltage of the power supply network, environmental conditions, and usage requirements.

2.1.13.2 Socket outlets with protective earthing shall be used.

2.1.13.3 In areas for children, socket outlets and light switches shall be placed at a height of 1.5 m above the finished floor, except where safety protective measures are provided.

2.1.13.4 In shops, restaurants, and other public buildings, normal lighting, emergency lighting, and exit lighting switches shall be installed in locations only accessible to managers for operation.

2.1.13.5 Enclosed type electric motors shall be used.

2.1.13.6 In case open type electric motors are used, they shall be installed in a separate compartment, with walls, ceilings, and floors made of non-combustible materials and shall be at least 0.5 m away from combustible parts of the building.

2.1.13.7 Electric motors for common use and their protective and control devices shall be installed in locations only accessible to managers.

2.1.13.8 Control buttons for common use electrical equipment shall be arranged at convenient operating locations and labeled for distinction.

2.1.13.9 In case electric motors need to be installed on the mezzanine floor, they shall not be installed directly above living rooms, working rooms, and shall ensure the permissible noise level according to current regulations.

2.1.14 Requirements for wiring systems and electrical equipment for artificial lighting and other usage purposes

2.1.14.1 The cross-sectional area of conductor cores and cables shall not be less than the values specified in 2.1.5.

2.1.14.2 Wiring systems serving the lighting of signboards attached to buildings shall have protective devices to disconnect the power supply in case of insulation failure or short circuit, or shall be enclosed inside building structures, or cables shall have insulation sheaths meeting standards and shall be run in force-resistant and heat-resistant plastic conduits, or other protective measures shall be provided.

2.1.14.3 Separate wiring systems shall be provided from the main distribution board to supply power to the lighting systems of staircases, common passages, corridors, and other rooms outside the scope of residential apartments.

2.1.14.4 Indoor lighting group wiring systems shall be protected by fuses or circuit breakers with a rated current not exceeding 25 A. For wiring systems supplying power to groups of high-power lighting equipment in public buildings, protection by fuses or circuit breakers with a rated current up to 63 A is allowed.

2.1.14.5 In case a common group wiring system supplies power to electric motors, the number of motors shall not exceed four, and the power of each motor shall not exceed 3 kW.

2.1.14.6 Lighting equipment of buildings shall:

a) Have illuminance levels suitable for the type of work, group of rooms, and buildings as specified in Appendix C;

b) Apply measures to limit reflected glare as specified in Appendix D.

2.1.14.7 Separate wiring systems shall be arranged for lifts and escalators from the main distribution board or from a distribution board dedicated for lifts and escalators.

2.1.14.8 Automatic water level control devices shall be attached to the control circuit of electric motors of water pumps for tanks and containers.

2.1.14.9 Ventilation systems, air conditioning systems, and electric resistance water heating systems shall be directly supplied by separate wiring systems from the distribution board and shall have automatic disconnecting protective devices.

2.2 Earthing system and protective conductors

2.2.1 General requirements

2.2.1.1 The earthing system consists of main components: earth electrodes, main earthing terminal (the connecting terminal or collecting bar for connecting electrical equipment to the earthing system), and earthing conductor (the conductor for connecting the main earthing terminal to the earth electrode) interconnected and shown in Appendix E.

2.2.1.2 The earthing system shall:

a) Be reliable and meet the requirements for protection and long-term operation of electrical equipment;

b) Be capable of withstanding fault currents without causing danger to persons or damage to equipment;

c) Not cause damage to different metal parts due to electrolytic effects;

2.2.2 Requirements for earth electrodes

2.2.2.1 The earth resistance of electrodes in the earthing system under the most unfavorable conditions shall meet the electric shock protection conditions specified in 2.4.2.3.

2.2.2.2 Pipelines carrying substances with the potential to cause fire or explosion shall not be used as part of an earth electrode.

2.2.2.3 Materials used for earth electrodes shall be resistant to electrolytic corrosion.

2.2.2.4 The minimum allowable materials and dimensions of components used for earth electrodes shall comply with the provisions in Appendix G.

2.2.3 Requirements for the main earthing terminal

2.2.3.1 In an earthing system using protective bonding, the following conductors shall be connected to the main earthing terminal:

a) Earthing conductor;

b) PE conductor;

c) Protective equipotential bonding conductor (hereinafter referred to as protective bonding conductor);

d) Functional earthing conductor, if any.

2.2.3.2 The main earthing terminal shall be arranged in an easily accessible location.

2.2.3.3 The main earthing terminal shall be capable of disconnecting each individual conductor from the connection. The connection shall be secure and only detachable using specialized tools.

2.2.4 Requirements for earthing conductors

The minimum allowable cross-sectional area of earthing conductors not buried in the ground shall be in accordance with the cross-sectional area of the PE conductor determined in 2.2.5.1e. In case of burial in the ground, the values specified in Table 1 shall be followed.

Table 1 – Minimum allowable cross-sectional area of earthing conductors buried in the ground

2.2.5 Requirements for PE conductors

2.2.5.1 PE conductors shall meet the following requirements:

a) PE conductors shall be protected against mechanical, chemical, and electrochemical damage, withstand electrodynamic forces and thermal effects under all operating conditions;

b) No switching devices shall be placed on PE conductors, and no connections shall be arranged, except for connections that can be disconnected using specialized tools;

c) The metal enclosure of equipment shall not be used as part of the PE conductor for other equipment;

d) Connections of PE conductors shall be easily accessible for inspection and testing, except for connections that are encapsulated or filled with fillers;

e) When checking the continuity of the earthing system, dedicated devices (such as sensing actuators, coils) shall not be connected in series with the PE conductor;

f) The cross-sectional area of PE conductors shall not be less than the values specified in Table 2.

Table 2 – Minimum allowable cross-sectional area of PE conductors

2.2.5.2 Conductors used as PE conductors include:

a) Conductors in multi-core cables;

b) Insulated or bare conductors, located in the same protective sheath as current-carrying conductors;

c) Fixed installed bare conductors or insulated conductors;

d) Cable sheaths or metal cabinets, cable armoring, steel sheaths of cables, braided steel wires, coaxial conductors, metal conduits that simultaneously meet the following requirements:

– Electrical continuity is ensured by suitable structures or connections, resistant to mechanical damage as well as electrochemical corrosion;

– Can be connected to other PE conductors at predetermined wire connection points;

– Have a cross-sectional area not less than the value specified in Table 2.

2.2.5.3 PE conductors that are not part of a cable or not located in a common protective sheath with phase conductors shall have a cross-sectional area not less than:

a) 2.5 mm² for mechanically protected conductors;

b) 4 mm² for conductors without mechanical protection.

2.2.5.4 The minimum allowable cross-sectional area of PE conductors used in common for multiple circuits shall be determined according to Table 3 with the fault current and duration corresponding to the largest thermal energy (I2× t).

2.2.5.5 The following metal parts shall not be used as PE conductors:

a) Water pipes;

b) Pipes containing gases or flammable liquids;

c) Parts and structures subjected to mechanical stress during normal operation;

d) Pipes and parts that can be bent or twisted (unless designed for those purposes);

e) Wire supports, wire hanging wires.

2.2.5.6 When the protective earthing conductor also serves as a functional earthing conductor, it shall simultaneously meet the requirements for PE conductors and the requirements for functional earthing.

2.2.5.7 If overcurrent protective devices are used for protection against electric shock, the PE conductor shall be in the same wiring route as the current-carrying conductors.

2.2.6 Requirements for protective bonding conductors

2.2.6.1 Protective bonding conductors connected to the main earthing terminal shall have a cross-sectional area not less than:

a) 6 mm² for copper conductors;

b) 50 mm² for steel conductors.

2.2.6.2 The protective bonding conductor connecting between two metal enclosures of equipment shall have a current-carrying capacity equal to or greater than the current-carrying capacity of the PE conductor with the smallest current-carrying capacity connected to those equipment enclosures.

2.2.6.3 The protective bonding conductor connecting between the metal enclosure of equipment and external conductive parts shall have a current-carrying capacity not less than 1/2 of the current-carrying capacity of the corresponding PE conductor.

2.3 Isolation, switching of electrical circuits and safety services

2.3.1 Isolating and switching devices

2.3.1.1 The following types of devices shall be used for isolating and switching electrical circuits:

a) Isolating switches, load switches, circuit breakers;

b) Plugs and socket outlets;

c) Fuses;

d) Dedicated connecting devices (without the need to remove conductors).

2.3.1.2 The moving contacts of all multi-pole isolating and switching devices need to be mechanically interlocked to ensure simultaneous opening and closing, except for contacts used for neutral conductors which may close before and open after other contacts.

2.3.1.3 Single-pole isolating and switching devices shall not be installed on neutral conductors regardless of whether the circuit is single-phase or three-phase.

2.3.2 PE conductors of electrical circuits

2.3.2.1 The PE conductor of an electrical circuit shall not be installed through the magnetic circuit of an RCD.

2.3.2.2 Other requirements related to PE conductors shall be implemented according to the provisions in 2.2.5.

2.3.3 Requirements for the use of RCD types

2.3.3.1 An RCD shall be capable of isolating all live conductors of the circuit it protects.

2.3.3.2 Current-operated RCDs shall be used, voltage-operated RCDs shall not be used.

2.3.3.3 When installing RCDs for three-phase circuits without three-phase loads, RCDs shall be used for each phase to reduce the scope of power loss when there are only faults in individual phases.

2.3.3.4 RCDs with an operating current not exceeding 30 mA shall be used as additional protection for electrical equipment in circuits using hand-held tools.

2.3.4 Short-circuit protection devices

2.3.4.1 The rated current of the protective device shall not be less than the maximum long-term operating current of the electrical circuit.

2.3.4.2 The protective device shall be capable of interrupting the maximum short-circuit current.

2.3.5 Emergency switching

2.3.5.1 In case it is necessary to disconnect the power supply to prevent unforeseen hazards, emergency switching devices shall be installed for the relevant part of the electrical system.

2.3.5.2 Emergency stop means shall be provided when electrically powered movements increase the hazard.

2.3.5.3 Emergency switching devices shall be capable of interrupting the current of the relevant equipment parts, taking into account the current of braked motors.

2.3.5.4 Emergency switching devices shall be capable of disconnecting power to all live conductors.

2.3.5.5 Devices used for emergency switching shall be painted red and arranged to be easily identified, easily accessible, and directly hand-operated to disconnect power supply circuits when conditions allow.

2.3.5.6 When the device has been switched off, it shall be locked or latched in the off position and ensured to have no possibility of automatically reconnecting.

2.3.6 Electrical systems used for safety services

2.3.6.1 A separate electrical system shall be provided to maintain the operation of essential parts for safety services at all times and under all conditions.

2.3.6.2 Safety services include, but are not limited to the following items:

a) Emergency lighting, exit lighting;

b) Fire fighting pumps;

c) Lifts for rescue in case of fire;

d) Alarm systems (fire, smoke, CO, intrusion);

e) Evacuation systems;

f) Smoke extraction systems;

g) Pressurization fan systems for emergency exit staircases;

h) Essential medical equipment.

2.3.6.3 In IT systems, a continuous insulation monitoring device shall be provided to generate an audible and visual signal when the first earth fault occurs.

2.3.7 Power sources used for safety services

2.3.7.1 Power sources used for safety services (batteries, independent generating sets, separate feeders independent from normal power supply feeders) shall have sufficient capacity, reliability, operating time, characteristic parameters, and appropriate switchover time as required.

2.3.7.2 Power sources used for safety services shall be permanently installed in a suitable location, with measures for ventilation and safe exhaust gas discharge to the outside. Faults in normal power sources shall not adversely affect these power sources.

2.3.7.3 Power sources used for safety services that are also used for other purposes shall not affect the main function. Measures shall be taken so that when there is a fault in the circuit supplying power for other purposes, it does not cause loss of power for safety services.

2.3.7.4 If a source used for safety services simultaneously supplies power to safety services of multiple buildings, a fault in the safety services of one building shall not affect the normal operation of that source.

2.3.8 Requirements for electrical circuits used for safety services

2.3.8.1 Electrical circuits of safety services shall be independent of other circuits.

2.3.8.2 When equipment is supplied from two different sources, a fault occurring in the circuit of one source shall not adversely affect the protection against electric shock or the correct operation of the other source. Equipment with a PE conductor shall have this PE conductor connected to the PE conductors of both circuits.

2.3.8.3 In case overload tripping causes loss of power supply that may lead to a greater hazard, the overload protective device shall not automatically disconnect the power supply but measures shall be taken to monitor the occurrence of overload for remediation.

2.3.8.4 Protection against short-circuit and electric shock under normal conditions and in case of a fault shall be ensured in any connection scheme with the normal power supply and the source used for safety services.

2.3.8.5 Overcurrent protective devices shall be selected and installed so as not to allow overcurrent in one circuit to affect the correct operation of the circuit used for safety services.

2.3.8.6 Distribution boards of safety services shall be isolated from components of the normal electrical system and shall ensure the required fire resistance duration.

2.3.8.7 Electrical circuits of safety services shall not pass through locations with fire risk, unless they are made of non-combustible materials or are appropriately protected. In all cases, electrical circuits shall not pass through areas with explosion risk.

2.3.8.8 Switching and control means shall be installed in groups, easily identifiable, located in areas only accessible to authorized persons.

2.3.8.9 Cables of electrical circuits used for safety services that are not of the fire-resistant or interference-resistant type shall be isolated from cables of other circuits, including cables of other safety circuits, by distance or barriers. Fire-resistant cables in accordance with the provisions in 2.1.9 shall be used to install in a way that ensures the necessary thermal and mechanical durability.

2.3.8.10 Electrical circuits used for safety services shall not be installed in lift shafts or any types of ventilation ducts or smoke ducts, except for cables used for rescue lifts in case of fire or lifts with special requirements.

2.3.8.11 Emergency lighting luminaires that normally do not operate shall automatically operate when there is a fault in the normal power supply circuit in the area where the luminaires are located. The switchover from normal mode to emergency mode shall be performed automatically when the normal source voltage is lower than 60% of the rated voltage for a period exceeding 0.5 s and automatically return to normal mode when the normal source voltage is greater than 85% of the rated voltage.

2.3.8.12 The power source used for emergency lighting shall be controlled at the distribution board. This provision does not apply to self-charging batteries.

2.3.8.13 In emergency lighting systems, the types of luminaires shall be compatible with the switchover time to maintain the specified illumination level.

2.3.8.14 At the central switching location, devices for monitoring and controlling the power supply shall be installed.

2.3.8.15 The minimum illuminance value of emergency lighting on the surface of passages and staircases shall be 0.5 lx, in rooms and escape areas it shall be 0.2 lx.

2.4 Protection against electric shock

2.4.1 Requirements for protection against electric shock due to direct contact

One of the following measures shall be used:

2.4.1.1 Completely enclosing live parts with insulating material meeting standards in such a way that it can only be removed by destruction.

2.4.1.2 Using barriers or enclosures that are securely fixed, ensure mechanical strength, are insulated from live parts in accordance with normal operating conditions, taking into account external influences, and tools or keys must be used to remove them, and have a minimum degree of protection of IPXXB or IP2X to prevent any contact of humans or animals with live parts. In case there are openings for replacing a part of the equipment, measures shall be taken to prevent accidental contact with live parts, and warnings shall be provided to avoid touching live parts;

Using barriers or enclosures with a minimum degree of protection of IPXXD or IP4X on the top horizontal surface that is easily accessible;

Parts that can be simultaneously accessible and have different voltages shall not be placed within the limits of the arm’s reach volume.

2.4.1.3 Using removable obstacles, but which cannot be accidentally displaced, to protect places where people may pass through or work and may accidentally come into contact with live objects.

2.4.2 Requirements for protection against electric shock due to indirect contact

2.4.2.1 Overcurrent protective devices shall be installed to automatically disconnect the electrical circuit in case of a fault.

2.4.2.2 For TT and TN-S schemes, RCDs shall be installed to protect against earth faults.

2.4.2.3 Measures shall be taken to ensure safety to avoid electric shock accidents to persons according to the condition

R_A × I_a ≤ 50 (1)

where:

– R_A is the earth resistance, in ohms (Ω);

– I_a is the operating current of the protective device, in amperes (A): For RCDs, it is the rated residual operating current I_Δn; For overcurrent protection, it is the value of the operating current of the protection at 5 s;

– 50 is the safety voltage value, in volts (V), accepted under normal conditions.

2.4.2.4 The metal enclosure of equipment shall be connected to the PE conductor according to the conditions specified for each type of earthing scheme in Appendix D.

2.4.2.5 Protective equipotential bonding of the building shall be connected to the PE conductor, earthing conductor, or earthing terminal, and external conductive elements. Conductors used for protective equipotential bonding shall comply with the provisions in 2.2.6.

2.4.2.6 Additional protection:

a) Supplementary equipotential bonding shall be connected to the accessible metal enclosures of equipment and conductive parts not belonging to the building electrical system, including the metal reinforcement core of reinforced concrete. The supplementary equipotential bonding system shall be connected to the PE conductor of all equipment, including the PE conductor of socket outlets.

The resistance R, in ohms (Ω), between any metal enclosures of equipment and any conductive parts not belonging to the building electrical system at locations where they can be simultaneously touched shall meet the condition

R ≤ 50 / I_a (2)

where:

– I_a is the operating current of the protective device, in amperes (A): For RCDs, it is the rated residual operating current I_Δn; For overcurrent protection, it is the value of the operating current of the protection at 5 s;

– 50 is the safety voltage value (in volts) accepted under normal conditions.

b) In case RCDs are used for additional protection, the rated residual operating current shall not exceed 30 mA.

2.4.2.7 Protection by electrical separation shall meet the following conditions:

a) Each source isolated from earth shall only supply one electrical equipment;

b) The separated circuit shall be supplied from an earthed isolated source and the voltage of the separated circuit shall not exceed 500 V;

c) Live parts of the separated circuit shall not be connected at any point to other circuits or to earth or to the PE conductor;

d) Cables and flexible cords of the circuit shall ensure visual control possibility along the length at risk of mechanical damage;

e) A separate wiring system shall be used for separated circuits;

f) In case of using conductors of the same wiring system for separated circuits and other circuits, non-metal sheathed multi-core cables shall be used or insulated conductors shall be used in insulating conduits, trunking systems, or boxes meeting the following conditions:

– The insulation of conductors shall meet the highest rated voltage present in the cable;

– Overcurrent protection shall be provided for each circuit;

g) Metal enclosures of equipment in separated circuits shall not be connected to earth or to the PE conductor or to the metal enclosures of equipment in other circuits.

h) In case there is more than one electrical equipment, in addition to the requirements stated in points b to g, the following provisions shall also be met:

– Measures shall be taken to protect the electrical circuit against insulation damage;

– The metal enclosures of the circuit, including socket outlets, shall be interconnected by an insulated conductor not connected to earth, not connected to the PE conductor or metal enclosures of other circuits;

– All flexible cables (unless supplying double insulated or reinforced insulated equipment) shall include a PE conductor to be used as an equipotential bonding conductor as stated in the second bullet point of this item;

– Automatic disconnection of the circuit shall be provided when a fault occurs at two points on two conductors connected to different terminals of the source with a maximum disconnection time specified in Table 3.

Table 3 – Maximum disconnection times applicable for final circuits with a rated current not exceeding 32 A

Time in seconds (s)

2.4.2.8 The earth resistance shall be ensured for overcurrent protective devices and RCDs to operate effectively.

2.5 Protection against thermal effects

2.5.1 General requirements

Protective measures shall be taken for humans, animals, fixed equipment, tools, and materials placed near electrical equipment and wiring to prevent harmful consequences due to heat from electrical equipment and wiring or due to thermal radiation causing ignition, damage, risk of burns or affecting safe operation.

2.5.2 Requirements for protection against fire caused by electrical equipment and wiring

2.5.2.1 Electrical equipment capable of generating surface temperatures that pose a fire risk to adjacent materials and objects when designed and permanently installed shall comply with one of the following requirements:

a) Placed on a base or in an enclosure made of materials that can withstand the temperature generated by that electrical equipment, are non-combustible, have low thermal conductivity, and have sufficient mechanical strength;

b) Isolated from adjacent materials, objects, or other elements by materials that can withstand the temperature generated by that electrical equipment, are non-combustible, have low thermal conductivity, and have sufficient thickness and mechanical strength;

c) Ensure a sufficiently large distance to adjacent objects or other elements to allow safe heat dissipation. All means of supporting electrical equipment capable of generating surface temperatures shall have low thermal conductivity.

2.5.2.2 When designing and installing building electrical systems, it is necessary to:

a) Use conductors with cross-sectional areas in accordance with the provisions in 2.1.5 and current loading levels in accordance with the provisions in 2.1.4.2;

b) Use RCDs with a maximum operating current of 0.5 A;

c) Ensure compatibility with environmental conditions, usage characteristics, architectural features of the building, and requirements for safety and fire protection techniques. In places with high fire risk, wiring systems and installation methods shall comply with the requirements specified in 2.1.2; 2.1.3.2 and 2.1.4.2.

2.5.2.3 Electrical equipment and wiring capable of producing arcs or electrical sparks during normal operation, when permanently connected, shall meet one of the following requirements:

a) Completely enclosed in arc-resistant, spark-resistant, non-combustible materials with low thermal conductivity and sufficient mechanical strength;

b) Isolated from objects or elements of the building by arc-resistant, spark-resistant, non-combustible materials with low thermal conductivity and sufficient mechanical strength;

c) Installed with a sufficient distance to ensure the extinction of arcs and electrical sparks.

2.5.2.4 Electrical equipment capable of causing heat concentration or heat accumulation shall have a sufficiently large distance to adjacent objects or elements of the building so that under normal operating conditions, it does not generate temperatures dangerous to objects and elements of the building.

2.5.2.5 For electrical equipment containing 25 l or more of flammable liquids placed in the same location, measures shall be taken to prevent the burning of those liquids and to prevent the spread of flames, smoke, and toxic gases from the fire to other parts of the building; power shall be disconnected as quickly as possible when a fire occurs.

2.5.2.6 Materials installed to shield around electrical equipment shall be materials with low thermal conductivity, fire resistance, and capable of withstanding the highest temperature that electrical equipment can generate.

2.5.3 Protective measures against fire from external sources

2.5.3.1 Locations of the building electrical system affected by external fire conditions shall comply with the relevant requirements specified in 2.5.1 and 2.5.2.

2.5.3.2 The design and installation of building electrical systems shall apply protective measures appropriate to the safe evacuation conditions of each area (areas with low population density and difficult evacuation conditions denoted as KV1; areas with high population density and easy evacuation conditions denoted as KV2; areas with high population density and difficult evacuation conditions denoted as KV3) in emergency situations.

Wiring systems shall not be installed on escape routes. In case it is mandatory to install, the wiring systems shall:

a) Have sheaths or enclosures that ensure no burning and causing fire for two hours;

b) Not be within the limits of the arm’s reach volume, unless protected against mechanical damage that may occur during evacuation;

c) Have the shortest length.

2.5.3.3 In KV2 and KV3 areas, switching, control, and protective devices (except for electrical equipment serving evacuation and escape) shall be arranged so that only authorized persons can access them. In case these devices are installed within the scope of passages, they shall be placed in cabinets or boxes made of non-combustible or fire-resistant materials.

2.5.3.4 In KV2, KV3 areas and in escape routes, electrical equipment containing flammable liquids shall not be used, except when these parts are enclosed in fire-resistant enclosures or boxes. Separate auxiliary capacitors installed in equipment are not subject to this provision.

2.5.3.5 For areas with high fire risk:

a) The use of electrical equipment in this area shall be limited. In case conductors are mandatory to pass through, they shall be sheathed with fire-resistant materials or have preventive measures to avoid causing fire or spreading flames. Conductor joints, if mandatory, shall be placed in fire-resistant boxes;

b) Measures shall be taken to prevent the accumulation of dust on the sheath of wiring and electrical equipment;

c) Electrical equipment with a structure or installation conditions such that the level of heat generation during normal operation or in case of a fault cannot cause fire shall be used;

d) Switching, protective, control, and isolating devices shall not be installed, unless placed in an enclosure with a degree of protection of at least IP4X;

e) Motors that are automatically or remotely controlled or without continuous operation supervision shall be protected against excessive temperature rise by temperature sensing devices;

f) Luminaires shall have an enclosure with a degree of protection of at least IP4X. Lamps and components of lighting equipment shall be protected in mechanically vulnerable places. Protective devices shall not be fixed on lamp holders, unless the lamp holders are designed for this purpose;

g) Electrical circuits shall be continuously monitored by insulation monitoring devices and have warnings in case of insulation faults;

h) Live parts of ELV circuits shall be ensured to be within an enclosure with a degree of protection of IP2X or IPXXB and capable of withstanding a test voltage with an r.m.s. value of 500 V for 1 min;

i) Measures shall be taken to ensure that electrical equipment cannot cause fire to the walls, floors, and ceilings of the building;

k) Measures shall be taken to prevent the building electrical system from causing fire propagation to structures with shapes and dimensions that are prone to flame propagation.

2.5.4 Requirements for protection against burns caused by electricity

2.5.4.1 The temperature of touchable parts of electrical equipment within the reach of persons shall not attain temperatures that can cause burns to persons and are specified as follows:

a) For hand-held means for operation, the temperature of touchable surfaces shall not exceed 55 oC if made of metal, and shall not exceed 65 oC if made of non-metallic materials;

b) For non-hand-held parts of equipment designed to be touched, the temperature of touchable surfaces shall not exceed 70 oC if made of metal, and shall not exceed 80 oC if made of non-metallic materials;

c) For parts of equipment not necessary to be touched during normal operation, the temperature of touchable surfaces shall not exceed 80 oC if made of metal and shall not exceed 90 oC if made of non-metallic materials.

2.5.4.2 All parts of the building electrical system capable of attaining temperatures exceeding the limits stated in 2.5.4.1 shall be protected to avoid accidental contact causing burns to persons.

2.5.5 Requirements for protection against overheating in heating locations

2.5.5.1 Forced hot air drying systems shall meet the following requirements:

a) Heating elements not belonging to the central heat accumulator shall not be allowed to operate if the specified air flow has not passed through and shall be cut off when the air flow is insufficient as specified;

b) Have two independently operating temperature control devices to prevent the temperature from exceeding the allowable limit in hot air ducts.

2.5.5.2 The frame and enclosure of heating elements shall be made of non-combustible materials.

2.5.5.3 Hot water or steam generating equipment shall have devices or means for protection against overheating under all operating conditions. In case this requirement is not met, overheating protection shall be implemented by a non-self-resetting mechanism operating independently of the temperature regulator.

2.5.5.4 Hot water or steam generating equipment with limited output shall have an additional mechanism for controlling the water pressure inside.

2.6 Protection against overcurrent

2.6.1 General requirements

2.6.1.1 The building electrical system shall have protective devices capable of interrupting all overcurrent conditions flowing in conductors before causing danger due to thermal and mechanical effects.

2.6.1.2 Current-carrying conductors shall be protected by devices capable of automatically disconnecting the power supply when these conductors are overloaded and short-circuited, except when the overcurrent is limited by the characteristics of the power source.

2.6.2 Requirements for overcurrent protection

2.6.2.1 The type of earthing system applied shall be considered to determine the measures for overcurrent protection.

2.6.2.2 Protection of phase conductors

Overcurrent protective devices shall be capable of interrupting the current in conductors subjected to overcurrent and shall be installed on all phase conductors.

2.6.2.3 Protection of neutral conductors

a) For TT and TN-S schemes:

In case the cross-sectional area of the neutral conductor is smaller than the cross-sectional area of the phase conductor, an overcurrent protective device corresponding to the cross-sectional area of the neutral conductor shall be installed. This protective device must disconnect the phase conductors, but not necessarily the neutral conductor. In case the current in the neutral conductor exceeds its current-carrying capacity, an overcurrent protective device shall be installed.

In all cases, the neutral conductor shall be protected against short-circuit current.

b) For IT scheme:

When the neutral conductor must be run along with the phase conductors, overcurrent protection shall be installed for the current-carrying conductors (including the neutral conductor) of each circuit, except in the following cases:

+ The neutral conductor is specifically effectively protected by the overcurrent protective device installed on the supply side or

+ The circuit is specifically protected by an RCD, whose rated residual current does not exceed 0.2 times the current-carrying capacity of the neutral conductor and the RCD disconnects all current-carrying conductors, including the neutral conductor of the corresponding circuit.

2.6.3 Requirements for protection against overload

2.6.3.1 In the building electrical system, overcurrent protective devices meeting the following two conditions simultaneously shall be used:

I_B ≤ I_n ≤ I_z (3)

and I₂ ≤ 1.45 × I_z (4)

where:

I_B is the design calculated current of the circuit, in amperes (A);

In is the rated current of the protective device, in amperes (A). For adjustable protective devices, the rated current In is the adjusted current;

I_Z is the long-term continuous current-carrying capacity of the conductor, in amperes (A);

I₂ is the effective operating current in the conventional time of the protective device, in amperes (A). The current I₂ is specified in the product standard or provided by the manufacturer.

2.6.3.2 Location for installing overload protective devices:

a) Overload protective devices shall be installed at locations where there is a change (in conductor cross-sectional area, installation method, structure) that reduces the permissible current-carrying capacity of the conductor, except for the cases specified in point b of 2.6.3.2 and in 2.6.4.

b) Overload protective devices may be installed on the conductor section between the point of change and the location of the protective device installation, if in this conductor section there are no branch circuits, no socket outlets, and one of the following two conditions is met:

– This conductor section is protected against short-circuit in accordance with the provisions in 2.6.5;

– This conductor section has a length not exceeding 3 m, has minimal short-circuit risk, reduces fire risk and danger to persons to the lowest level.

2.6.4 Requirements for overload protection of parallel conductors

2.6.4.1 If there is only one protective device for multiple parallel conductors, there shall be no branch circuits, isolating devices, or switching devices on those parallel conductors.

2.6.4.2 In case there is only one protective device for multiple parallel conductors where the current in the conductors is considered to be evenly distributed (if the difference between the currents in any conductors and the design current for each conductor does not exceed 10%), the value Iz mentioned in 2.6.3.1 is the total current-carrying capacity of the conductors.

2.6.4.3 In case multiple conductors must be used in one phase and the current in the conductors is uneven, the design current and overload protection requirements for each conductor shall be calculated specifically and considered separately.

2.6.5 Requirements for short-circuit protection

2.6.5.1 The prospective short-circuit current at each relevant point of the building electrical system shall be determined through calculation or measurement.

2.6.5.2 Location for installing short-circuit protective devices

a) Short-circuit protective devices shall be installed at locations where the conductor cross-section is reduced or there are other changes that alter the permissible current in the conductor, except for the cases specified in points b, c of this section and in 2.6.5.3.

b) In case short-circuit protective devices are installed at a location different from that specified in point a of this section, in the conductor section (from the location of the protective device installation to the location of cross-section reduction or other change), there shall be no branch circuits and socket outlets, not longer than 3 m, installed in a way that minimizes the risk of short-circuit and not near combustible materials;

c) In case short-circuit protective devices are installed on the supply side of the location where the conductor changes (cross-section or other changes), those devices shall have operating characteristics that meet the requirements for short-circuit protection of the wiring on the load side, similar to the case of being installed on the load side.

2.6.5.3 Short-circuit protection of parallel conductors

a) In case of using a single short-circuit protective device for multiple parallel conductors, the operating characteristics of that protective device shall:

– Ensure effective operation when a fault occurs at the most critical point of one of the parallel conductors;

– Take into account the distribution of short-circuit current between parallel conductors and the current that may flow from both ends of the parallel conductors to the fault point.

b) If the operation of a single protective device is not effective, one or more of the following measures shall be used:

– Wiring shall be installed to minimize the risk of short-circuit in any conductor and the risk of fire;

– For circuits with two parallel conductors, short-circuit protective devices shall be used at the supply end of each conductor;

– For circuits with more than 2 parallel conductors, short-circuit protective devices shall be installed at both the supply and load ends of each conductor.

2.6.5.4 Short-circuit protective devices shall meet the following characteristics:

a) The breaking capacity of each short-circuit protective device shall not be less than the prospective short-circuit current at the location of the short-circuit protective device installation, except in the following cases:

– On the supply side, there is already another protective device with sufficient breaking capacity; the let-through energy by these two devices shall not exceed the let-through energy that the device on the load side and the protected conductor can withstand;

– For devices on the load side, in addition to the let-through energy, other detailed characteristics shall be considered as specified by the manufacturer;

b) For cables and insulated conductors, all currents caused by a short-circuit at any point in the circuit shall be interrupted before the insulation of the conductor heats up to the allowable temperature limit;

c) When the operating time of the protective device is less than 0.1 s, the level of current asymmetry is high and there is a current-limiting device, the value (k×S)2 shall be greater than the let-through energy (I2×t). The value (k×S)2 is specified by the manufacturer.

For short-circuit times extending up to 5 s, the time t for the temperature of the conductors to rise from the maximum allowable temperature under normal conditions to the limit temperature can be approximately determined by the formula

t = ( k×S / I )² (5)

where:

t is the short-circuit duration, in seconds (s);

k is the factor taking into account the resistivity, temperature coefficient, heat capacity of the conductor material, initial and final temperatures respectively. For commonly used conductor insulation, the value of the factor k is specified in Appendix H;

S is the cross-sectional area of the conductor, in square millimeters (mm²);

I is the r.m.s short-circuit current, in amperes (A).

d) For busbar systems, the rated short-circuit withstand current shall not be less than the calculated short-circuit current.

2.6.6 Requirements for coordination of overload and short-circuit protection

2.6.6.1 Protection by the same device (overload protection simultaneously with short-circuit protection) shall meet both the provisions stated in 2.6.3 and 2.6.5.

2.6.6.2 Protection by separate devices

a) Overload protective devices shall meet the provisions stated in 2.6.3. Short-circuit protective devices shall meet the provisions stated in 2.6.5.

b) The characteristics of the devices shall be coordinated so that the let-through energy by the short-circuit protective device does not exceed the let-through energy that the overload protective device can withstand.

2.6.7 Limiting overcurrent by the characteristics of the power supply source

Conductors are considered to be protected against overload and short-circuit when they are supplied from a power source that is incapable of generating a current exceeding the current-carrying capacity of the conductors such as isolating transformers, bell transformers, welding transformers, certain types of generators (gasoline, diesel powered).

2.7 Protection against voltage disturbances and electromagnetic disturbances

2.7.1 Requirements for protection against temporary overvoltages due to earth faults

2.7.1.1 Measures shall be taken to minimize the impact on the building electrical system of power-frequency fault voltages (the voltage between the metal enclosures of equipment and earth, denoted as Uf) and power-frequency stress voltages (the voltage between phase conductors and metal enclosures of equipment at substations, denoted as U1, and between phase conductors and metal enclosures of equipment in the building electrical system, denoted as U2) when high-voltage short-circuit faults occur (shown in Appendix I).

2.7.1.2 The value and duration of Uf shall not exceed the voltage value determined by the curve Uf(t) in Appendix K.

2.7.1.3 The value and duration of U1 and U2 shall not exceed the values given in Table K.1 of Appendix K.

2.7.1.4 In case U1 and U2 are greater than the values stated in Table K.1 of Appendix K, the following measures shall be taken:

a) Separate earthing between high voltage and low voltage at distribution substations;

b) Change the earthing scheme in the low-voltage electrical system;

c) Reduce the earth resistance of substations.

2.7.2 Requirements for protection against impulse overvoltages

2.7.2.1 The rated impulse withstand voltage of electrical equipment shall not be less than the required impulse withstand voltage level specified in Appendix L.

2.7.2.2 Electrical equipment at the starting point of the building electrical system (from the main distribution board) shall have the ability to withstand Category IV impulse voltage (Category IV overvoltage) with large amplitude.

2.7.2.3 Switching devices, conductors, collecting bars, junction boxes of the building electrical system permanently installed from the main distribution board to the equipment on the load side shall have the ability to withstand Category III impulse voltage (Category III overvoltage).

2.7.2.4 Permanently installed electrical equipment without special requirements for availability shall have the ability to withstand Category II impulse voltage (Category II overvoltage).

2.7.2.5 Equipment containing electronic circuits, in which protective measures must be implemented outside the equipment and are not permanently connected to the public power grid, shall have the ability to withstand Category I impulse voltage (Category I overvoltage).

2.7.2.6 Overvoltage protective devices shall be installed to prevent consequences related to human life, public services, commercial activities.

2.7.2.7 In case the building electrical system is supplied from a system with overhead lines (except for cables with sheathing and grounded metal protection layer) and the number of thunderstorm days is greater than 25 days/year, atmospheric overvoltage protective devices with a protection level not higher than Category II overvoltage level shall be installed.

2.7.3 Requirements for protection against undervoltage

2.7.3.1 Appropriate preventive measures shall be taken in case of voltage sag or loss and subsequent restoration, which may cause danger to persons and equipment.

2.7.3.2 When reconnection causes danger, it shall not be done automatically.

2.7.4 Measures against electromagnetic effects

2.7.4.1 Measures to reduce electromagnetic effects include:

a) Metal sheath of cables shall be connected to the common equipotential bonding;

b) Avoid the possibility of mutual inductance between electrical circuits, signal circuits, and data circuits;

c) Electrical cables and signal cables shall be electrically separated from each other and, if practically possible, placed at right angles to each other;

d) Use multi-core symmetrical cables for electrical connection between frequency converters and speed-controlled motors;

e) Electrical cables and signal cables shall be placed separately from down conductors of LPS (conductors that create a low resistance path to connect the air termination system to the earth network so that lightning currents are safely conducted to earth) or separated by magnetic shields;

f) When switching the power supply of the TN-S system, devices that simultaneously switch three phase conductors and the neutral conductor shall be used;

g) When switching single-phase power supply, devices that simultaneously switch the phase conductor and the neutral conductor shall be used.

2.7.4.2 Earthing and equipotential bonding shall be used for protection against electromagnetic interference for electrical circuits with a large number of important communication and application equipment.

2.8 Lightning protection

2.8.1 General requirements

2.8.1.1 LPS (including internal LPS and external LPS) shall meet the requirements for protection against direct lightning strikes to buildings.

2.8.1.2 The necessity of lightning protection for buildings shall be determined based on the location with the possibility of being struck by lightning and the level of damage caused by lightning strikes.

2.8.1.3 Metal structures of the building shall be utilized for LPS to reduce costs, but shall not affect the quality and aesthetics of the building.

2.8.1.4 The entire building shall be protected by a completely interconnected LPS, with no part of the building being separated for individual protection.

2.8.2 External LPS

2.8.2.1 The protection zone is determined by the rolling sphere method. In case the building height is lower than 20m, it is determined by the protection angle method.

2.8.2.2 The external LPS includes the following components: air termination system, down conductors, and lightning protection earth network (including horizontal or vertical electrodes interconnected with each other).

2.8.2.3 Thermally isolated LPS shall be used with the building when there is a possibility of heat generation and explosion at the points of lightning strike capture and conduction.

2.8.2.4 The air termination system (lightning rods or mesh conductors or a combination of both) shall be arranged to meet the following requirements:

a) Placed at positions on the building not within the protection zone determined by the methods specified in 2.8.2.1;

b) In case the roof of the building is made of combustible materials, it shall be placed at least 0.1 m away from the roof, for thatched roofs it shall be 0.15 m.

2.8.2.5 Down conductors shall meet the following requirements:

a) The number of down conductors shall not be less than 02 and evenly distributed around the perimeter (in accordance with the architectural shape) of the building;

b) The maximum distance between down conductors shall be in accordance with the provisions in Table 4;

Table 4 – Maximum distance between down conductors according to LPS class

c) Down conductors shall follow the shortest path to the ground;

d) Down conductors shall be placed at least 0.1 m away from combustible surfaces of the building.

2.8.2.6 The lightning protection earth network shall meet the following requirements:

a) The earth resistance shall not be greater than 10 Ω;

b) In case the earth network is used in common for LPS and other equipment, the earth resistance shall be suitable for the related equipment;

c) It shall be possible to isolate it from the down conductors and a reference earth electrode shall be arranged for measurement and testing. The connection point to the earth network shall be accessible from the ground surface for convenient inspection and maintenance of the LPS.

2.8.2.7 The materials and dimensions of the components of the external LPS shall comply with the requirements specified in Appendix M.

2.8.3 Internal LPS

2.8.3.1 The internal LPS includes the components of the equipotential bonding network, SPDs, magnetic shields.

2.8.3.2 The internal LPS shall be implemented by one of the following solutions:

a) Electrical isolation between the external LPS and conductive elements not belonging to the building electrical system in accordance with the provisions in 6.3 of TCVN 9888-3:2013;

b) Lightning equipotential bonding by interconnecting the LPS with:

– Metal structures;

– Internal systems of the building;

– External conductors and conductive parts connected to the building.

2.8.3.3 Other lightning protection solutions

a) Use magnetic shields to attenuate the electromagnetic field of lightning impulses;

b) Use SPDs or spark gaps to limit transient overvoltages and surge currents.

2.8.4 Buildings higher than 60 m

2.8.4.1 Air termination systems shall be installed to protect the part of the building above 60 m and the equipment installed on it (especially the top 20% of the building height when this part is at a height exceeding 60 m from the ground).

2.8.4.2 The installation location of the air termination system in the part above 60 m of the building shall meet at least lightning protection level IV.

2.8.4.3 In case of utilizing existing external metal structures of the building as air termination systems, their dimensions shall meet the requirements specified in Appendix M.

2.8.5 Buildings containing flammable or explosive materials or having hazardous areas

Lightning protection of buildings containing flammable or explosive materials and buildings with hazardous areas shall meet the requirements stated in Appendices D.4 and D.5 of TCVN 9888-3:2013.

2.8.6 Buildings with antennas

Antennas placed on the roof of the building shall be within the protection zone of the LPS and shall be connected to the LPS.

2.8.7 Erection of structures

During the erection of structures, all large and protruding steel sections shall be effectively earthed. From the start of the LPS installation, continuous earthing shall be maintained.

2.9 Connection of separate power sources

2.9.1 General requirements

2.9.1.1 When connecting separate power sources (other than the public power grid) to the building electrical system, safety requirements shall be met.

2.9.1.2 The connection of separate power sources is specified for the following cases:

a) The building electrical system is not connected to the public power grid;

b) The separate power source serves as a backup power source for the normal power supply;

c) Separate power sources operate in parallel with each other or with the public power grid;

d) A combination of the above cases.

2.9.2 Safety requirements when supplying power from separate power sources

2.9.2.1 The frequency, voltage, phase sequence of the separate power source connected to the building electrical system shall be compatible with the frequency, voltage, and phase sequence (for three-phase power sources) of the building electrical system. When bringing power sources into parallel operation, an additional condition regarding the phase angle deviation between the voltages of the sources shall be met.

2.9.2.2 Prospective short-circuit currents, earth fault currents, and short-circuit protective devices in the building electrical system shall be suitable for each case stated in 2.9.1.2.

2.9.2.3 Measures shall be taken to partially shed the load of the building electrical system when the separate power source is overloaded.

2.9.3 Safety measures when switching to backup power source

2.9.3.1 The backup power source is a power source to maintain the power supply to all or part of the building electrical system when the normal power supply is interrupted.

2.9.3.2 Measures shall be taken to prevent incorrect operation when switching power sources.

2.9.4 Requirements for separation of neutral conductors

The neutral conductor of the backup power source shall be installed separately from the neutral conductor of the normal power source.

2.9.5 Overload protection for backup generators for fire pumps

The overload protective device of the backup generator for fire pumps shall only give an audible warning signal by bell or siren, and shall not automatically disconnect the power of this generator.

2.10 Electrical equipment in special areas

2.10.1 General requirements

The building electrical system in special areas (areas with special activities or special conditions) shall meet all the requirements of this Regulation with additions or modifications specified in 2.10.2 to 2.10.6.

2.10.2 Requirements for areas with bathtubs or showers

2.10.2.1 The building electrical system at the location of bathtubs, showers, and the surrounding space shall be designed and installed in accordance with the requirements for ensuring electrical safety.

2.10.2.2 The classification into three zones 0, 1, and 2 according to the level of electrical hazard is specified in Figures N.1 and N.2 of Appendix N.

2.10.2.3 When using ELV supplied from SELV or PELV sources, all electrical equipment shall be protected against direct contact by barriers or enclosures with a minimum degree of protection of IPXXB or IP2X; insulated to withstand a test voltage with an r.m.s. value of 500 V AC for 1 min. Protection against direct contact by obstacles or placing out of arm’s reach is not allowed.

2.10.2.4 Additional protective measures shall be taken by supplementary equipotential bonding, using RCDs with a rated residual operating current not exceeding 30 mA for all electrical circuits, except for circuits that are electrically separated and supply only a single equipment and use SELV or PELV sources.

2.10.2.5 The degree of protection of electrical equipment (according to Appendix B) installed in zone 0 shall be IPX7; in zones 1 and 2 shall be IPX4. In case water jets can be sprayed in zones 1 and 2, it shall be IPX5.

2.10.2.6 Wiring systems supplying equipment located in zones 0, 1, 2 shall be implemented as follows:

a) Buried in the wall at a depth of at least 5 cm;

b) Run horizontally or vertically on the outside of the wall, then penetrate through the wall behind the equipment.

2.10.2.7 Switching and control devices shall not be placed in zone 0.

2.10.2.8 In zone 1, accessories, including socket outlets of circuits supplied from SELV or PELV sources, shall have a rated voltage not exceeding 25 V. The power source shall be placed outside zones 0 and 1.

2.10.2.9 In zone 2, accessories, including socket outlets of circuits, shall be supplied from SELV or PELV sources. The power source shall be placed outside zones 0 and 1.

2.10.2.10 Electrical equipment used in zone 0 shall simultaneously meet the following conditions:

a) According to the manufacturer’s instructions;

b) Connected permanently and long-term;

c) Using ELV from SELV sources.

2.10.2.11 Electrical equipment used in zone 1 shall simultaneously meet the following conditions:

a) According to the manufacturer’s instructions;

b) Connected permanently and long-term.

2.10.3 Requirements for swimming pools and fountains

2.10.3.1 The building electrical system at locations with swimming pools, fountains, and adjacent areas shall be designed and installed in accordance with the requirements for electrical safety.

2.10.3.2 The classification into three zones 0, 1, and 2 according to the level of electrical hazard is specified in Figures N.3, N.4, and N.5 of Appendix N. The equipment room of the swimming pool is considered to be outside zones 1 and 2.

2.10.3.3 The use of obstacles, placing out of arm’s reach to protect against electric shock due to direct contact shall not be applied. Protection measures using non-conductive floors, walls, non-earthed equipotential bonding, separated circuits supplying multiple electrical equipment shall not be used.

2.10.3.4 All external conductive elements shall be connected to the PE conductor of the metal enclosures of electrical equipment located in zones 0, 1, 2 (supplementary local equipotential bonding). In zones 0 and 1 of swimming pools, ELV not exceeding 12 V from SELV sources placed outside zones 0 and 1 shall be used. In other cases, extra-low voltage shall be used, with sources placed outside zones 0 and 1 and supplying only a single equipment, or automatic disconnection by RCDs with operating current not exceeding 30 mA, or by separated circuits in zones 0 and 1 of fountains and zone 2 of swimming pools.

2.10.3.5 PELV sources shall not be used for protection by ELV. When using SELV sources, protection against direct contact with all electrical equipment shall be provided by barriers or enclosures with a minimum degree of protection of IP2X or IPXXB; insulated to withstand a test voltage with an r.m.s. value of 500 V AC for 1 min.

2.10.3.6 The protective conductor of the equipotential bonding ring of all external conductive elements not belonging to the building electrical system capable of bringing in potential from outside into zones 0, 1, 2 shall be connected to the PE conductor of the metal enclosure of the equipment located in those zones.

2.10.3.7 Electrical equipment with a degree of protection corresponding to the IP code shall be used as specified in Table 5.

Table 5 – Minimum permissible IP code of electrical equipment

2.10.3.8 Wiring systems

a) In zones 0, 1, and 2, wiring systems shall not have metal sheaths capable of being contacted; metal sheaths not capable of being contacted shall be connected to the supplementary equipotential bonding.

b) In zones 0 and 1, wiring systems for supplying equipment outside those zones shall not be placed.

c) Wiring systems placed in zone 2 or on walls, ceilings, floors delimiting the zones to supply equipment located outside those zones shall be buried at a depth of at least 5 cm, or protected by an RCD with operating current not exceeding 30 mA, or using SELV sources, or using separated circuits.

d) Cable types confirmed by the manufacturer to be able to have frequent contact with water shall be used for installation in fountains.

e) In fountains not intended for persons to enter, cables or conductors in non-metallic conduits to supply equipment located in zone 0 shall be placed on the edge of the pool, as far away from the pool as possible and routed to the equipment by the shortest path; cables and conductors in non-metallic conduits placed in zones 0 and 1 shall be appropriately mechanically protected.

f) Junction boxes shall not be arranged in zone 0. In zone 1, only junction boxes for circuits from SELV sources shall be used.

2.10.3.9 Switching and control devices

a) Switching and control devices shall not be installed in zone 0;

b) In case switching and control devices, socket outlets are placed in zone 1, circuits from SELV sources shall be used and the power source shall be placed outside zones 0 and 1; if the power source is placed in zone 2, the supply circuit for this power source shall be protected by an RCD with operating current not exceeding 30 mA;

c) In case switching and control devices, socket outlets are placed in zone 2, one of the following protective measures shall be used:

– Using SELV sources and the power source shall be placed outside zones 0 and 1; If the power source is placed in zone 2, the supply circuit for this source shall be protected by an RCD with operating current not exceeding 30 mA;

– Automatic disconnection of the power supply together with additional protection using an RCD with operating current not exceeding 30 mA;

– Using a separated circuit, separately supplied by an isolating source, placed outside zones 0 and 1 and if the source supplying the separated circuit is placed in zone 2, the supply circuit for this source shall be protected by an RCD with operating current not exceeding 30 mA.

2.10.3.10 Other equipment of swimming pools

a) Electrical equipment used in zones 0 and 1 shall be equipment specifically designed for swimming pools and permanently installed.

b) Permanently connected cleaning equipment used in zones 0 and 1 shall be supplied from SELV sources with voltage not exceeding 12 V, with power sources placed outside zones 0 and 1; If the power source is placed in zone 2, it shall be implemented in accordance with the provisions in 2.10.3.9.c.

c) Water supply pumps or electrical equipment specifically designed for swimming pools located in the pump room adjacent to the pool and accessible through a door shall be protected by one of the following methods:

– Using SELV sources, voltage not exceeding 12 V, with sources placed outside zones 0 and 1, and if the source is placed in zone 2, it shall be implemented in accordance with 2.10.3.9.

– Using a separated circuit, with the following conditions:

+ The pump or other equipment connected to the pool uses non-conductive water pipes;

+ The pump room can only be opened by a key or tool;

+ All electrical equipment placed in the pump room has a minimum degree of protection of IPX5 or has an enclosure with the same degree of protection;

– Automatic disconnection of the power supply and simultaneously meeting the following conditions:

+ The connecting pipe from the pump (or other equipment) to the pool shall be of the type made of non-conductive materials, in case of metal pipes, they shall be connected to the equipotential bonding of the pool;

+ The door of the pump room can only be opened by a key or tool;

+ Electrical equipment placed in the pump room shall have a minimum degree of protection of IPX5 or have an enclosure with this degree of protection;

+ A supplementary equipotential bonding ring shall be arranged;

+ Electrical equipment shall be protected by an RCD with operating current not exceeding 30 mA;

d) Underwater luminaires in contact with the water of the swimming pool shall comply with the standards for underwater installation. Luminaires placed in a watertight recess in the pool wall, supplied and operated from behind, shall be installed so as not to create an electrical path, whether accidental or intentional, between the luminaire enclosure and the conductive parts of the luminaire recess.

2.10.3.11 Electrical equipment in zones 0 and 1 of fountains shall be designed and installed to be inaccessible.

2.10.3.12 Special requirements for the installation of low-voltage electrical equipment in zone 1 of swimming pools

a) Fixed equipment specifically designed for swimming pools, supplied with low voltage, shall simultaneously meet the following conditions:

– Have an enclosure equivalent to supplementary insulation and have impact protection;

– Comply with the provisions in 2.10.3.11;

– When opening the door where the equipment is located, it shall automatically disconnect the circuit of all conductors supplying power to the equipment inside; cables and means for disconnecting the electrical circuit shall have class 2 insulation or equivalent.

b) Luminaires supplied from sources other than SELV – 12 V installed on walls or ceilings in zone 1 of swimming pools without zone 2 shall have a circuit protected by automatic disconnection of the power supply and have additional protection by an RCD with operating current not exceeding 30 mA and the height of the lowest part of the luminaire shall be at least 2 m from the lower limit of zone 1.

2.10.3.13 Floor and ceiling heating:

Electrical heating elements buried under the floor shall be protected by one of the following two measures:

a) SELV with power sources placed outside zones 0 and 1. If placed in zone 2, it shall be implemented in accordance with 2.10.3.10;

b) Automatic disconnection of the power supply. The heating element shall be covered by a mesh or metal plate buried and connected to the supplementary equipotential bonding; the supply circuit shall have additional protection by an RCD with operating current not exceeding 30 mA.

2.10.4 Requirements for rooms or cabins containing steam-generating heating elements

2.10.4.1 Measures shall be taken to ensure safety for the building electrical system supplying power to on-site steam cabins and rooms containing steam-generating heating elements or steam-generating heating appliances (hereinafter collectively referred to as steam rooms).

2.10.4.2 The requirements of 2.10.4 do not apply to prefabricated steam cabins. Areas with cold water bathtubs or showers shall be implemented in accordance with the provisions in 2.10.2.

2.10.4.3 The classification into three zones 1, 2, and 3 according to the level of electrical hazard is specified in Figure N.6 of Appendix N.

2.10.4.4 Safety measures

a) When using SELV and PELV sources for protection, protection against direct contact for all electrical equipment shall be implemented by one of the following two measures:

– Using barriers or enclosures with a minimum degree of protection of IPXXB or IP2X;

– Using types with insulation capable of withstanding a test voltage of 500 V AC r.m.s. for 1 min;

b) Protection against direct contact by obstacles, by placing out of arm’s reach shall not be applied;

c) Additional protection shall be provided for all electrical circuits of the steam room, except for steam-generating heating elements or steam-generating heating appliances, by using one or more RCDs with operating current not exceeding 30 mA;

d) Protective measures against indirect contact using non-conductive floors, walls, and non-earthed equipotential bonding shall not be used.

2.10.4.5 Electrical equipment shall have a minimum degree of protection of IP24. If cleaning by water jets is expected, electrical equipment shall have a minimum degree of protection of IPX5.

2.10.4.6 In zone 1, no electrical equipment shall be placed, except for steam-generating heating elements or steam-generating heating appliances. In zone 3, installed equipment shall withstand a temperature of at least 125 oC and the insulation layer of conductors shall withstand a temperature of at least 170 oC.

2.10.4.7 In case it is mandatory to place in zones 1 and 3, wiring systems shall withstand the temperature specified in 2.10.4.6; metal conduits and metal sheaths of cables shall be designed and installed to be inaccessible during normal operation.

2.10.4.8 Switching and control devices shall be installed outside the steam room or steam cabin, except when these switching and control devices are a part of steam-generating heating elements or steam-generating heating appliances or other equipment permanently installed in zone 2 according to the manufacturer’s instructions.

2.10.4.9 Socket outlets shall not be arranged inside the steam room.

2.10.5 Requirements for medical locations

2.10.5.1 The building electrical system in medical locations (places for receiving, examining, treating, cosmetic procedures, monitoring, and caring for patients) and veterinary hospitals shall meet the requirements for electrical safety. This provision does not apply to medical electrical equipment.

2.10.5.2 Measures shall be taken to ensure electrical safety for three groups of medical locations including:

a) Group 0 is a medical location that does not use applied parts (a part of medical electrical equipment that, in normal use, necessarily comes into physical contact with the patient, or can be brought into contact with the patient, or needs to be touched by the patient).

b) Group 1 is a medical location that uses applied parts externally to the patient’s body or inserted into any part of the patient’s body;

c) Group 2 is a medical location that uses applied parts for work where loss of power will cause danger to the patient’s life.

2.10.5.3 The building electrical system in medical locations shall meet the requirements for switching priority loads from the normal power source to the backup power source.

2.10.5.4 Safety measures

a) Protection by insulation enclosure or barriers is the main measure.

b) In case of using SELV and PELV in areas of groups 1 and 2, the rated voltage of electrical equipment shall not exceed 25 V. In areas of group 2, metal enclosures of equipment shall be connected to the equipotential bonding ring.

c) Protection measures by obstacles and placing out of arm’s reach shall not be applied.

d) The accepted safety voltage limit shall not be greater than 25 V.

e) Final circuits of the TN-S scheme in areas of group 1 with currents up to 32 A shall have RCDs with operating current not exceeding 30 mA. In areas of group 2, RCDs with operating current not exceeding 30 mA shall not be used except for circuits supplying operating tables; mobile X-ray equipment brought into areas of group 2; equipment with rated power greater than 5 kVA; non-essential equipment (not related to sustaining human life).

In areas of groups 1 and 2, RCDs other than types A and B shall not be used;

f) For TT scheme: In areas of groups 1 and 2, all provisions stated in Point e shall be implemented and in all those cases, RCDs shall be used;

g) For IT scheme: The IT scheme shall be used for circuits supplying medical electrical equipment that are critical to the patient’s life, surgical equipment, and equipment in the patient vicinity (the space in which the patient can directly or through others touch parts of medical electrical equipment) in areas of group 2 (other than group 2 equipment stated in Point e).

Each group of rooms with the same function shall use a separate IT scheme. In the IT scheme, there shall be an insulation monitoring device meeting the following requirements:

– The total AC resistance of the monitoring device shall not be less than 100 kΩ;

– The measuring voltage of the monitoring device shall not be greater than 25 V DC;

– The measuring current, even in case of a fault, shall not be greater than 1 mA;

– When the insulation resistance of the monitored circuit drops to 50 kΩ, the monitoring device shall give a warning; there shall be a device to determine the location of the insulation fault.

Each IT scheme used in medical locations shall have an audible and visual warning signal placed at a location where the staff of the medical unit can monitor; there shall be a unit for monitoring overload and temperature of medical transformers in the IT scheme;

h) In each medical location of groups 1 and 2, there shall be a supplementary equipotential bonding ring in the patient vicinity.

2.10.5.5 Requirements for electrical equipment in medical locations shall be implemented in accordance with clause 710.5 of TCVN 7447-7-710:2006.

2.10.5.6 Inspection during commissioning and periodic inspection shall be implemented in accordance with clause 710.6 of TCVN 7447-7-710:2006.

2.10.6 Requirements for electrical equipment for lighting by ELV

2.10.6.1 Protection against electric shock and overcurrent protection:

a) The lighting system by ELV shall use SELV sources;

b) Power sources for SELV sources shall be permanently installed. Transformers in the secondary circuit operating in parallel shall be connected in parallel in the primary circuit and have identical electrical characteristics. When transformers operate in parallel, the primary circuit shall be permanently connected to a common isolating device for isolation and switching;

c) SELV circuits shall be protected against overcurrent by a common protective device or protective devices used for each SELV circuit.

2.10.6.2 Fire protection:

a) Luminaires and luminaire accessories shall be designed and installed to avoid thermal hazards to surrounding materials and environment;

b) Equipment and conductors of the lighting system by ELV shall meet fire protection requirements.

c) Manufacturer’s instructions shall be followed, including instructions for installation on combustible or non-combustible surfaces;

d) Transformers shall be short-circuit proof and protected on the primary side in accordance with the following requirements:

– Continuously monitor the current of the luminaires;

– Automatically disconnect the power supply within 0.3 s if the circuit power exceeds 60 W;

– Ensure safety even in case of a fault.

2.10.6.3 The wiring system for lighting by ELV shall:

a) Have conductors placed in conduits, boxes;

b) Comply with the requirements of the lighting system using incandescent lamps;

c) Comply with the requirements of the contact rail system used for lighting;

d) Not use parts of the building structure as electrical conductors.

2.10.6.4 Conductor cross-sectional areas shall meet the following requirements:

a) Conductors connected to the output of the power source (transformer or converter) shall be suitable for the load current;

b) In case of suspending luminaires on conductors connected to the output of the power source, the cross-sectional area according to mechanical strength shall not be less than 4 mm².

2.10.6.5 Isolating devices, switching devices, protective devices, and other devices used in the lighting system by ELV shall meet the following requirements:

a) Arranged at easily accessible locations;

b) Have signs indicating the installation location of protective devices;

c) Have labels or identification signs for electrical circuits and protection purposes;

d) Permanently installed at false ceiling locations or similar;

e) Use energy-saving luminaires, meeting requirements for illuminance and safety;

f) Protective devices permanently installed in the electrical circuit;

g) SELV sources and their protective devices shall be installed to ensure:

– Avoidance of mechanical impact on electrical connections;

– Safe support or protection;

– No overheating due to insulation.

3. INSPECTION PROVISIONS

3.1 General requirements

3.1.1 The building electrical system shall be inspected before acceptance for commissioning and inspected according to maintenance requirements.

3.1.2 During inspection, measures shall be taken to ensure safety for persons and equipment.

3.1.3 The inspection consists of two steps as follows:

a) Visual inspection;

b) Inspection by testing.

3.1.4 After completion of the work, the inspector shall sign a document certifying the inspection results.

3.2 Requirements for visual inspection

3.2.1 Visual inspection shall be carried out when the building electrical system is de-energized and before inspection by testing.

3.2.2 Visual inspection shall include at least the following contents:

a) Measures to ensure safety against electric shock;

b) Measures to ensure safety against fire propagation;

c) Selection and installation of protective and monitoring devices;

d) Selection and installation of conductors;

e) Selection and installation of switching and isolating devices;

f) Selection and installation of equipment and protective measures appropriate to external influences;

g) Correct identification of neutral conductors (N conductors) and PE conductors;

h) Availability of diagrams together with necessary information on distribution boards;

i) Identification of electrical circuits;

k) Condition of connections;

l) Full and appropriate presence of PE conductors, including main and supplementary equipotential bonding rings;

m) Accessibility for operation and maintenance;

n) Single-pole switching devices not installed on N conductors;

o) Selection and installation of LPS.

3.3 Requirements for inspection by testing

3.3.1 Testing shall be carried out (if there are elements to be inspected) according to the following main contents:

a) Continuity of PE conductors, main and supplementary equipotential bonding circuits;

b) Insulation resistance of the building electrical system;

c) Protective measures by separated circuits; SELV or PELV sources;

d) Insulation resistance of insulating floors and walls;

e) Additional protective measures by high sensitivity RCDs;

f) Automatic disconnection of the power supply;

g) Phase sequence;

h) Functional testing;

i) Earth resistance of LPS.

3.3.2 In case of test results not meeting requirements, errors shall be found and corrected, then retesting shall be carried out, including previous tests whose results may be affected.

3.3.3 The continuity of PE conductors, including main and supplementary equipotential bonding circuits, shall be tested using DC or AC sources.

3.3.4 Measure the insulation resistance between each pair of current-carrying conductors and between each current-carrying conductor and earth of the building electrical system; The measurement results shall not be lower than the values specified in Table 6.

Table 6 – Minimum permissible insulation resistance

3.3.5 Testing of protective measures by ELV and separated circuits shall be carried out by measuring the insulation resistance between the ELV circuit or separated circuit with connected electrical equipment and other circuits and earth; The measurement results shall not be lower than the values specified in Table 6.

3.3.6 Appropriate devices shall be used to measure the insulation resistance of insulating floors and walls; The measurement results shall be greater than 50 kΩ.

3.3.7 The operation of high sensitivity RCDs used as a means in additional protective measures shall be tested.

3.3.8 Checking the conditions of protective measures by automatic disconnection of the power supply for protection against direct contact shall be carried out as follows:

a) For TN-S scheme: Measure the total impedance of the fault loop Z_s; The measurement results shall meet the condition

Z_s × I_a ≤ U_o (6)

where:

Z_s is the total impedance of the fault loop, including the power supply source, current-carrying conductors, PE conductors from the power supply source to the fault point, in ohms (Ω);

Ia is the current for the protective device to operate and disconnect the power within the specified time range, in amperes (A);

U_o is the voltage between the phase conductor and earth, in volts (V).

b) For TT scheme: Measure the earth resistance of the building electrical system; The measurement results shall meet the condition specified in 2.4.2.3.

c) For IT scheme:

– Calculate or measure the current when the first fault occurs;

– Measure the fault current if this current cannot be calculated due to not knowing all the parameters of the circuit;

– Check the fault condition and test similarly to the TN-S earthing scheme (phase-to-phase short circuit) when the second fault occurs.

3.3.9 The phase sequence of the building electrical system shall be tested.

3.3.10 Check the correct functioning of equipment combinations.

4. IMPLEMENTATION ORGANIZATION

4.1 The Ministry of Construction is responsible for disseminating and guiding the application of this Regulation.

4.2 State management agencies for construction are responsible for organizing the inspection and supervision of the implementation of this Regulation in the activities of design, design appraisal, construction, acceptance for commissioning, and maintenance in accordance with the provisions of current laws.

4.3 During the implementation of this Regulation, if there are any difficulties, all opinions shall be sent to the Ministry of Construction for guidance and handling.

APPENDIX A (Regulation) Limits of the arm’s reach volume

NOTE: S is the surface where persons are active.

Figure H.1 – Determination of the limits of the arm’s reach volume

APPENDIX B (Regulation) Degree of protection of electrical equipment

The IP Code of electrical equipment indicates the degree (level) of protection of electrical equipment placed in enclosures, boxes, or protective grids. Specifically as follows:

– The first digit (from 0 to 6) following the letters IP indicates the degree of protection against solid objects:

0- not protected;

1- protected against solid objects larger than 50 mm (e.g. accidental contact by hand);

2- protected against solid objects larger than 12.5 mm (e.g. fingers);

3- protected against solid objects larger than 2.5 mm (e.g. tools, screws …);

4- protected against solid objects larger than 1 mm (e.g. small tools, wires);

5- dust-protected (dust deposits not allowed);

6- dust-tight.

– The second digit (from 0 to 8) following the letters IP indicates the degree of protection against ingress of water:

0- not protected;

1- protected against vertically falling water drops;

2- protected against vertically falling water drops when tilted up to 15° from the vertical;

3- protected against water falling as rain at an angle of up to 60° from the vertical;

4- protected against splashing water from all directions;

5- protected against water jets from all directions;

6- protected against powerful water jets from all directions;

7- protected against the effects of temporary immersion in water;

8- protected against the effects of continuous immersion in water.

When the first digit (or second digit) is replaced by the letter X, it means that the degree of protection against solid objects (or against ingress of water) is not addressed.

Following the digits, the following letters may be added with the meaning of protection against accidental access by:

A – back of hand;

B – finger;

C – tool;

D – wire.

After the first letter, a second letter may be added with the following meaning:

H – high voltage electrical apparatus;

M – motion during water test;

S – stationary during water test;

ω – weather conditions.

– Examples:

An enclosure with the symbol IP34 means:

3 – protection against ingress of solid foreign objects with diameters 2.5 mm and greater, protection against accidental access with a tool having a diameter of 2.5 mm and greater;

4 – protection of the internal equipment against the harmful effects of water splashed from all directions.

An enclosure with the symbol IP23CS means:

2 – protection against ingress of solid foreign objects with diameters 12.5 mm and greater; Protection against accidental access with a finger;

3 – protection of the internal equipment against the harmful effects of rainwater falling at an angle of up to 60°;

C – protection against accidental contact with hazardous parts inside with a tool having a diameter of 2.5 mm and a length of 100 mm;

S – during the water test, the internal electrical equipment is in a stationary state (for example, the rotor of a rotating electric machine).

APPENDIX C (Regulation) Artificial lighting

Table C.1 – Minimum illuminance allowed according to work characteristics

NOTE:

When there are requirements for hygiene or specialty (such as dining rooms, kitchens, sales areas of stores, operating rooms, auditoriums, engine rooms, etc.), it is allowed to increase the illuminance value by one step according to the following illuminance scale:

Table C.2 – Minimum illuminance allowed on the working surface when using a general artificial lighting system in residential and public buildings

APPENDIX D (Regulation) Necessary measures to limit reflected glare

Table D.1 – Necessary measures to limit reflected glare from working surfaces with specular and mixed reflection characteristics when performing class I, II, III tasks

a – Working surface made of metal or white plastic

b – Working surface made of ceramics or dark materials

c – Surface capable of diffusing light under a layer of translucent material or a diffusing surface

LEGEND:

1 – Eye of the worker;

2 – Viewing direction of the eye;

3 – Luminous surface of the lamp;

4 – Working surface;

5 – Working surface with light diffusing properties;

6 – Layer of translucent material.

Figure D.1 – Arrangement of lamps, working surface and eyes of the worker

APPENDIX D (Regulation) Types of earthing schemes

D.1 Definition and symbols of earthing schemes

D.1.1 Definition of earthing scheme

An earthing scheme is the relationship to earth of the following two elements:

– The neutral point of the power supply source;

– The metal enclosures of equipment at the point of utilization.

D.1.2 Symbols of types of earthing schemes

Consists of 2 or 3 letters:

– The first letter: indicates the relationship to earth of the neutral point of the power supply source by one of the following two letters:

T (Terre-French) – the neutral point is directly earthed;

I (Isolé-French) – the neutral point is isolated from earth or earthed through a high impedance (thousands of ohms).

– The second letter: indicates the relationship to earth of the metal enclosures of equipment at the point of utilization by one of the following two letters:

T – the metal enclosure is directly earthed;

N – the metal enclosure is connected to the neutral point N of the power supply source (this point is already directly earthed).

– The third letter:

S (Séparé-French) – the neutral conductor and the PE conductor are separate.

This Regulation specifies the following three types of earthing schemes: IT; TT; TN-S.

D.2 IT scheme

– The neutral point of the power supply source: isolated from earth or earthed through a high impedance (thousands of ohms);

– The metal enclosure of equipment at the point of utilization: directly earthed.

a – Without neutral conductor

b – With neutral conductor

Figure D.1 – IT scheme

NOTES:

1. Figure D.1 does not show the impedance (which may exist) connecting the neutral point of the power supply source to earth;
2. In the IT scheme, the neutral conductor is not run, except in case the equipment uses phase voltage, then the main insulation of each phase shall withstand the line voltage.

D.3 TT scheme

– The neutral point of the power supply source: directly earthed;

– The metal enclosure of equipment at the point of utilization: directly earthed.

Figure D.2 – TT scheme

D.4 TN-S scheme

– The neutral point of the power supply source: directly earthed;

– The metal enclosure of equipment at the point of utilization: connected to the neutral point of the source by a separate conductor called the protective conductor (PE conductor);

– The N conductor and the PE conductor are separate;

– The N conductor is not earthed, the PE conductor is earthed repeatedly as many times as possible.

Figure D.3 – TN-S scheme

APPENDIX E (Regulation) Earthing system and protective conductors

Figure E.1 – Earthing system and protective conductors

NOTES:

M metal enclosure of equipment capable of being touched, normally not live but will become live when insulation fails;

Conductive parts not belonging to the building electrical system include:

C1 incoming metal water pipes;

C2 outgoing metal waste water pipes;

C3 incoming metal gas pipes with an insulating sleeve;

C4 air conditioning;

C5 heating system;

C6 metal water pipes, for example in bathrooms;

C7 conductive parts not belonging to the building electrical system within arm’s reach from exposed conductive parts;

B main earthing terminal.

Earth electrodes include:

T1 foundation earth electrode;

T2 earth electrode for lightning protection, if necessary;

1 PE conductor;

2 protective bonding conductor;

3 supplementary protective bonding conductor;

4 down conductor of LPS;

5 earthing conductor.

APPENDIX G (Regulation) Materials and minimum allowable dimensions of components used for earth electrodes

Table G.1 – Minimum allowable dimensions of components used for earth electrodes made of common materials considering corrosion resistance and mechanical strength

APPENDIX H (Regulation) Values of the factor k for conductors

Table H.1 – Values of the factor k for conductors

APPENDIX I (Regulation) Temporary overvoltages on the low-voltage side when an earth fault occurs on the high-voltage side of the transformer

a – In TT and TNS schemes

b – In IT scheme

Figure I.1 – Analysis of fault voltages

LEGEND:

I_E earth fault current in the high-voltage electrical system flowing through the earth network of the distribution substation (BAPP);

R_E earth resistance of the earth network of the BAPP;

R_B earth resistance of the low-voltage neutral earthing network at the BAPP;

R_A earth resistance of the protective earth network of the building electrical system;

U₀ nominal phase-to-neutral voltage of the low-voltage network;

U_f power-frequency fault voltage appearing between the metal enclosure of equipment and earth of the building electrical system;

U₁ power-frequency stress voltage appearing between the phase conductor and the metal enclosure of the BAPP during a fault;

U₂ power-frequency stress voltage appearing between the phase conductor and the metal enclosure of equipment in the building electrical system during a fault;

I_h short-circuit current flowing through the protective earth network of the building electrical system when a phase-to-earth fault occurs in the high-voltage network and a phase-to-earth fault occurs at the first point in the low-voltage network with the IT earthing scheme;

I_d short-circuit current flowing through the protective earth network of the building electrical system when a fault occurs in the low-voltage network with the IT earthing scheme;

Z total impedance between the low-voltage neutral point and the earth network (with a high value) in the IT earthing scheme.

When an earth fault occurs on the high-voltage winding of the BAPP, the temporary overvoltages appearing in the low-voltage network are determined according to Table I.1.

Table I.1 – Temporary overvoltages in the low-voltage network

APPENDIX K (Regulation) Requirements for temporary overvoltages

The magnitude and duration of the power-frequency fault voltage U_f appearing in the building electrical system between the metal enclosure of equipment and earth shall not be greater than the value of U_f determined by the curve U_f(t) in Figure K.1.

Figure K.1- Permissible fault voltage U_f due to short-circuits in the high-voltage electrical system

Table K.1 – Permissible power-frequency stress voltage

APPENDIX L (Regulation) Required impulse withstand voltage of equipment

Table L.1 – Required impulse withstand voltage of equipment

APPENDIX M (Regulation) Materials and minimum allowable dimensions of components of external LPS

Table M.1 – Materials, configurations and minimum allowable cross-sectional areas of air-termination conductors, down conductors of LPS

Table M.2 – Materials, configurations and minimum allowable cross-sectional areas of earth-termination system of LPS

APPENDIX N (Regulation) Classification of zones according to the level of electrical hazard

a – Side view, area with bathtub	b – Floor plan view
c – Floor plan view (with fixed partition and radius determining the minimum distance around the partition)	d – Side view, area with shower

Figure N.1 – Dimensions of zones in areas with bathtubs or showers with a basin

a – Side view	b – Side view (with fixed partition and radius determining the minimum distance from the top of the partition)
c – Floor plan view (with different positions of fixed water outlets)

d – Floor plan view with fixed water outlets (with fixed partition and radius to determine the minimum distance around the partition)

LEGEND: – Water outlet

Figure N.2 – Dimensions of zone 0 and zone 1 in areas with showers without a basin

Figure N.3 – Dimensions of zones of a sunken swimming pool (vertical projection)

Figure N.4 – Dimensions of zones of a raised swimming pool (vertical projection)

Figure N.5 – Dimensions of zones of a swimming pool (floor plan view)

Figure N.6 – Dimensions of zones in the vicinity of steam-generating heating elements