CIRCULAR

Regulations on National Technical Standards for Electrical Engineering

 ________________________

THE MINISTER OF INDUSTRY AND TRADE

Pursuant to the Law on Standards and Technical Regulations dated June 29, 2006 of the National Assembly of the Socialist Republic of Vietnam;

Pursuant to the Electricity Law dated December 3, 2004 of the National Assembly of the Socialist Republic of Vietnam;

Pursuant to Decree No. 189/2007/ND-CP dated December 27, 2007, issued by the Government, detailing the functions, tasks, powers, and organizational structure of the Ministry of Industry and Trade;

WHEREAS, Decree No. 127/2007/NĐ-CP dated August 1, 2007 of the Government detailing and guiding the implementation of certain provisions of the Law on Technical Standards and Regulations;

Pursuant to Circular No. 23/2007/TT-BKHCN dated September 28, 2007 of the Ministry of Science and Technology guiding the development, review, and issuance of technical standards;

Pursuant to the proposal of the Director of the Science and Technology Department,

c) Enterprises may be granted permission for no more than one block out of the total three dual-frequency blocks (FDD) B

Article 1. Issued with this Circular are the National Technical Standards for Electrical Engineering:

- Volume 8: Low Voltage Electrical Standards

Code: QCVN QTĐ-8:2010/BCT

(Volumes 1, 2, 3, and 4 were issued pursuant to Decision No. 19/2006/QĐ-BCN dated July 11, 2006 of the Minister of Industry issuing Electrical Equipment Regulations; volumes 5, 6, and 7 were issued pursuant to Circular No. 40/2009/TT-BCT dated December 31, 2009).

Article 2. This Circular shall take effect from April 1, 2011.

Article 3. Ministries, ministerial-level agencies, agencies under the Government, People's Committees of provinces and centrally governed cities, and relevant organizations and individuals are responsible for implementing this Decision./.

2.4.4. Support for Multi PLP

PART I .GENERAL PROVISIONS

Article 1. Scope of Regulation

Article 2. Applicability

Article 3. Explanation of Terms

Article 5. Safety Protection

Article 6. Characteristics of Power Supply Sources

Article 7. Selection of Electrical Equipment

Article 8. Installation and Commissioning of Electrical Systems Before Operation

Chapter II. MAIN CHARACTERISTICS OF ELECTRICAL EQUIPMENT SYSTEMS

Article 9. Required Capacity

Article 10. Principles for Determining Distribution Diagrams

Article 11. Power Supply

Chapter III. PROTECTION OF ELECTRICAL EQUIPMENT

Section I: ELECTRIC SHOCK PROTECTION

Article 12. Protection Against Direct Contact

Article 13. Protection Against Indirect Contact

Section II: PROTECTION AGAINST HEAT EFFECTS

Article 14. General Requirements

Article 15. Fire Protection

Article 16. Selection of Fire Protection Measures Based on External Conditions

Section III: PROTECTION AGAINST OVERCURRENT

Article 17. General Requirements

Article 18. Overload Protection

Article 19. Short Circuit Protection

Article 20. Coordination Between Overload and Short Circuit Protection

Article 21. Limiting Overcurrent Through Source Characteristics

Section IV: PROTECTION AGAINST OVERVOLTAGE AND ELECTROMAGNETIC INTERFERENCE

Article 22. General Provisions

Article 23. Protection of Low Voltage Equipment Against Temporary Overvoltages and High Voltage Earth Faults

Article 24. General Requirements for Overvoltage Protection

Chapter IV: SELECTION AND INSTALLATION OF ELECTRICAL EQUIPMENT

Section I: GENERAL PRINCIPLES

Article 25. General Requirements for Electrical Equipment

Article 26. Operating Conditions and External Influences

Article 27. Accessibility

Article 28. Marking and Identification

Article 29. Prevention of Harmful Mutual Interference

Section II: CONDUCTOR SYSTEMS

Article 30. General Requirements

Article 31. Pre-Made Busway Systems

Article 32. Selection and Installation Considering External Influences

Article 33. Current Carrying Capacity

Article 34. Conductor Cross-Section

Article 35. Electrical Connections

Article 36. Selection and Installation of Electrical Conductors to Limit Fire Spread Within Buildings

Article 37. Selection and Installation for Maintenance and Cleaning

Article 38. General Requirements

Article 39. Equipment for Indirect Contact Protection by Disconnecting the Power Supply

Article 40. Equipment for Overcurrent Protection

Article 41. Equipment for Overvoltage and Electromagnetic Interference Protection

Article 42. Isolation equipment and disconnection devices

Section IV: EARTHING EQUIPMENT AND PROTECTIVE CONDUCTORS

Article 43. General requirements

Article 44. Earthing

Article 45. Protective conductors

Article 46. Earthing equipment for protective purposes

Article 47. Earthing equipment for operational purposes

Article 48. Earthing equipment for both protective and operational purposes

Article 49. Equal potential bonding conductors

Section V: OTHER EQUIPMENT

Article 50. Low-voltage generator sets (LVGS)

Article 51. Safety equipment

Article 52. Lighting equipment for safety services

APPENDIX TABLE

Appendix 1: Permissible alternating voltage stress

Appendix 2: External conditions

Appendix 3: Maximum operating temperature with different types of insulation

Type of insulation

Appendix 4 Minimum cross-sectional area of conductors

Appendix 5: Surge withstand voltage according to rated voltage

Appendix 6: Cross-sectional areas of earthing conductors

Appendix 7: Values of k for insulated protective conductors not in direct contact with Cable sheaths or bare protective conductors in contact with Cable sheaths

Appendix 8: Values of k for single-core protective conductors within multi-core cables

Appendix 9: Values of k for bare conductors where there is no risk of damage to adjacent materials due to heat generated

Appendix 10 Minimum cross-sectional area of protective conductors

PART I

GENERAL PROVISIONS

Article 1. Scope of Regulation

1. These standards specify the design, installation, and operation rules for alternating current electrical equipment systems with a maximum rated voltage up to 1000 V and a frequency of 50 Hz.

2. These standards do not apply to electric traction equipment, electrical equipment systems of transportation means (cars, ships, aircraft, etc.), public lighting electrical equipment systems, underground mine electrical equipment systems, electric fences, lightning protection equipment for buildings, special structures and equipment.

3. Public power supply systems shall comply with the current equipment standards.

Article 2. Applicability

These standards shall be compulsorily applied to organizations and individuals involved in the design, installation, and operation of alternating current electrical equipment systems with a maximum rated voltage up to 1000 V and a frequency of 50 Hz.

Article 3. Explanation of Terms

The following terms shall be understood as follows:

1. An electrical equipment system is a set of electrical equipment and conductor systems for producing or consuming electrical energy.

2. The point of entry of the electrical system (the power supply point for electrical equipment) is the starting point of the electrical equipment installation connected to the distribution network. An electrical equipment system may have one or more points of entry.

3. Ambient temperature is the temperature of the surrounding environment where the equipment is installed and operated, including the influence of the temperature of other equipment installed and operated at the same location.

4. Live parts, live conductors are conductors and parts expected to carry electricity during normal operation, which include phase conductors and neutral conductors.

5. Exposed conductive parts are conductive parts outside the electrical equipment installation that can be: metal structures of buildings, metal pipes for gas or water, uninsulated walls and floors.

6. Equipment enclosures are exposed conductive parts (made of metal) that can be touched.

7. Neutral conductor: conductor connecting from the neutral point (the neutral point of a three-phase electrical equipment system is the common point of the windings of the phases connected in star).

8. Protective conductor: conductor directly connecting the enclosures of electrical equipment to the earthing equipment at the point of use..

9. Parts that can be simultaneously contacted are metallic parts that a person can simultaneously touch.

10. Direct contact protection means contacting a live part simultaneously with another conductive part, equipment enclosure, exposed conductive part, protective conductor.

11. Indirect contact protection is protection when contacting conductive parts including equipment enclosures, exposed conductive parts, protective conductors in case of main insulation failure.

12. Main power supply is the power supply for the electrical equipment system during normal operation..

13. Standby power supply is the power supply when the main power supply is lost to ensure some work must continue to operate to avoid equipment damage and work interruption.

14. Emergency power supply: When an accident (fire, explosion, building collapse, etc.) causes loss of the main power supply and standby power supply, but some services still need to be supplied with power for emergency purposes such as alarm signals, lighting, escape routes, smoke exhaust fans, emergency evacuation elevators, etc. Safety requirements are usually stipulated by competent authorities (fire prevention agencies, labor protection agencies, etc.).

15. Reach distance: The area limited by lines that a person standing or moving on a surface can reach with one hand without using a ladder or any other tool.

Article 4. Objectives

The installation and design of electrical equipment systems aim to ensure safety in the design, installation, and operation of low-voltage electrical equipment systems in residential buildings, commercial facilities, industrial facilities, agricultural facilities, public works...

Article 5. Safety Protection

1. General Requirements

The requirements in this standard aim to ensure safety for people, livestock, property, and prevent dangers and damage that may occur during the use of electrical equipment systems.

2. Protection against electric shock

a) Direct contact protection: People must be protected from hazards that may arise when coming into contact with live parts of the electrical equipment system;

b) Indirect contact protection: People must be protected from hazards that may arise when coming into contact with the enclosures of equipment due to insulation failure.

3. Protection against thermal effects

Electrical equipment systems must be arranged so as to eliminate all risks of igniting flammable materials due to excessively high temperatures or electric sparks. Additionally, during normal operation, the electrical equipment system must not cause burns to human bodies.

4. Protection against overcurrent

People and property must be protected from dangers or damage caused by excessively high temperatures or mechanical forces generated by overcurrent.

5. Protection against fault currents

Conductors, other than those carrying current and other parts used to carry fault currents, must have sufficient capacity to carry such currents without reaching excessively high temperatures.

6. Protection against overvoltage

People and property must be protected from harmful consequences resulting from insulation breakdown between live parts of circuits with different voltages.

People and property must be protected from harmful consequences resulting from overvoltages caused by other reasons (atmospheric overvoltages, switching overvoltages).

Article 6. Characteristics of Power Supply Sources

The characteristics of the source must be compatible with the number of conductors, rated values, and permissible deviations, as well as with the grounding scheme and other controls related to the method of protection..

1. Cross-sectional area of conductors

The cross-sectional area of conductors must be determined based on:

a) The maximum allowable temperature of the conductors;

b) Permissible voltage drop;

c) Electromechanical forces that may occur in the event of a short circuit;

d) Other mechanical forces that may act on the conductors;

e) The maximum allowable total resistance ensuring the operation of short-circuit protection devices.

2. Protective devices

The type of protective device must be determined according to the function of the device, for example, to protect against overcurrent (overload and short circuit), earth fault current, overvoltage, low voltage, or loss of voltage;

Protective devices must operate at appropriate current, voltage, and time values corresponding to the characteristics of the circuit to prevent potential hazards.

3. Emergency power supply disconnecting devices

If it is necessary to disconnect the power supply circuit urgently when there is a risk of losing safety, the disconnection device must be arranged to be easily recognizable and operable.

4. Isolation

Devices must be arranged to allow complete isolation of the electrical system or a circuit or individual equipment for maintenance, inspection, fault location, and repair purposes.

5. Independence of the electrical equipment system

The electrical system must be arranged to exclude any harmful mutual influences between the electrical system and other systems in the building.

6. Accessibility of electrical equipment

Electrical equipment must be arranged in accordance with the following requirements to the extent necessary:

a) There must be sufficient space for initial installation and subsequent replacement;

b) There must be accessibility to perform necessary operations during operation, inspection, maintenance, and repair.

Article 7. Selection of Electrical Equipment

1. General Requirements

Electrical equipment installed in electrical equipment systems must comply with national product standards.

2. Characteristics

The characteristics of electrical equipment must correspond to the conditions and specific characteristics determined for the electrical system, and also meet the following provisions:

a) Regarding voltage

Electrical equipment must be suitable for the maximum value of voltage (for alternating current, the effective value) supplied by the power source during normal operation and any overvoltages that may occur.

b) Regarding current

The selected electrical equipment must take into account the maximum value (for alternating current, the effective value) of current passing through during normal and abnormal operation.

c) Regarding frequency

If frequency affects the operation of electrical equipment, the frequency of the equipment must match the possible frequency of the power grid.

d) Regarding power

Electrical equipment selected on the basis of the maximum power consumed during normal operation, taking into account the utilization factor and operating conditions.

3. Installation Conditions

Electrical equipment must be selected so that it can withstand the forces acting upon it and the surrounding environmental conditions specific to the installation site.

4. Avoiding Harmful Effects

Electrical equipment must be selected so that it does not create harmful effects on people, other equipment, or the power grid during normal operation, including during operation, such as power factor, starting current, phase imbalance, higher harmonic waves,...

Article 8. Installation and Commissioning of Electrical Systems Before Operation

1. Installation Construction

Personnel installing the electrical system must have the capability and appropriate construction equipment;

The characteristics of the selected electrical equipment must not be reduced during installation;

Conductors must be marked for identification by color or number;

Connections between conductors and other equipment must be made to ensure long-term secure contact;

Electrical equipment must be installed to ensure necessary cooling conditions;

Electrical equipment capable of generating high temperatures or creating electric arcs must be arranged or protected so as to eliminate all risks of igniting other materials. The outer parts of electrical equipment that may reach temperatures harmful to human health must be arranged or protected to prevent any accidental contact.

2. Pre-operation inspection

New or modified electrical systems must be tested before being put into operation to ensure compliance with current standards.

Chapter II

MAIN CHARACTERISTICS OF ELECTRICAL EQUIPMENT SYSTEMS

Article 9. Required Capacity

Power requirements must be calculated during the design of the electrical system to ensure economic stable operation and safety for the equipment to operate within permissible temperature and voltage drop ranges.

When determining the power requirement of electrical equipment or a group of electrical devices, the simultaneous factor must be taken into account.

Article 10. Principles for Determining Distribution Diagrams

The electrical distribution diagram must be designed and installed in accordance with the electrical load requirements.

1. The electrical distribution diagram is determined based on

a) The electricity supply requirements of each load consumer;

b) The type of electrical network wiring diagram;

c) The type of grounding diagram.

2. Types of electrical wiring diagrams

In this standard, the following types of electrical wiring systems supplying the electrical installation are considered:

a)Single-phase, two-wire system;

b)Single-phase, three-wire system;

c)Three-phase, three-wire system;

d)Three-phase, four-wire system;

e)Three-phase, five-wire system.

3. Grounding diagram of the electrical distribution system must also be compatible with the grounding status of the source:

a) Source with neutral grounded;

b) Source completely isolated from ground.

Article 11. Power Supply

1. General Requirements

For power sources (main source, backup source, emergency source), whether external or internal to the electrical installation, the following characteristics must be determined:

a) Frequency;

b) Rated voltage;

c) Calculated short-circuit current value at the system input;

d) Ability to meet system requirements, including power supply requirements.

2. Backup power source and emergency power source

The electrical installation must have an emergency power source to provide electricity for fire safety and evacuation work when the main power source is lost, as stipulated by current regulations.

Emergency power sources must be specified with characteristics to meet power capacity, reliability, readiness, and operational time requirements.

3. Maintenance capability

When installing power sources, the maintenance capability of the electrical installation throughout its operating period must be considered.

When maintaining power sources operated by another entity, the opinion of that entity must be sought.

The cycle and volume of maintenance tasks must be defined to ensure:

a) Regular periodic inspections, tests, maintenance, and repairs can be easily carried out;

b) Ensuring the effectiveness of safety protection devices;

c) Ensuring the reliability of equipment throughout the life of the installation.

Chapter III

PROTECTION OF ELECTRICAL EQUIPMENT

Section I

ELECTRIC SHOCK PROTECTION

Article 12. Protection Against Direct Contact

1. Protection by insulating covering of live parts

a) Live parts must be completely covered with insulating material that can only be removed by destruction.

b) Insulating protective material must be durable and resistant to mechanical, chemical, and thermal effects. Paints, varnishes, or similar products cannot be considered as insulating materials to protect against direct contact.

2. Protection by barriers or enclosures

2.1 Live parts must be located inside enclosures or behind barriers to ensure safe distances. If openings are necessary for replacement of components such as lamps, plugs, or fuses, or for operation of equipment, then:

a) Appropriate measures must be taken to prevent accidental contact with live parts;

b) Adequate warnings must be provided to inform people about the presence of live parts accessible through openings and not to touch them intentionally.

2.2 Barriers and enclosures must be securely fixed in place, stable, and mechanically robust to maintain the required level of protection and isolate live parts from normal operating conditions, taking into account external influences.

2.3 When it is necessary to remove barriers or enclosures or part of an enclosure, it can only be done using:

a) Locks or tools, or;

b) After disconnecting power to the live parts within the protected area, and restoring power can only be done after replacing or closing the removed barriers or enclosures;

c) Temporary barriers with at least IP2X protection level to prevent contact with live parts, such barriers can only be removed by unlocking or using tools.

3. Protection by obstacles

Obstacles used to prevent accidental contact with live parts but do not prevent intentional contact by going around the obstacles.

3.1 Obstacles must prevent:

a) Accidental human body contact with live parts, or;

b) Accidental contact with live parts during repair of operating energized equipment.

3.2 Obstacles can be removed without tools but must ensure accidental removal is prevented.

4. Protection by placing out of reach

Protection by placing out of reach is aimed solely at preventing unintentional contact with live parts.

5. Additional protection by residual current devices

Residual current devices are used to enhance protection against electric shock during normal operation.

5.1 Using residual current devices with a residual current limit not exceeding 30 mA is considered supplementary protection against electric shock during normal operation, in cases where other protective measures fail or due to user carelessness.

5.2 Using these devices does not constitute the sole protective measure and does not exempt from the requirements of applying one of the measures prescribed for direct contact protection.

Article 13. Protection Against Indirect Contact

1. Protection by automatic disconnection of supply

The power supply must be automatically cut off when there is a risk that contact voltage could harm human bodies.

Protective devices must automatically disconnect the power supply so that when there is an insulation fault between a live part and the equipment casing or a protective conductor, the contact voltage exceeding 50V shall not persist for a time sufficient to cause harmful effects on people. Regardless of the value of the contact voltage, in certain cases depending on the type of earthing system, the maximum allowable disconnection time may be up to 5 seconds.

2. Earthing

The metal casings of equipment must be connected to earth or to a protective conductor according to the conditions specified for each type of earthing system.

Metal casings of equipment that can be simultaneously approached must all be connected to a separate, group, or overall earthing installation.

3. Equal Potential Bonding

3.1 Main Equal Potential Bonding Loop

In each building, the following electrically conductive elements must be connected to the main equal potential bonding loop:

a) The main protective conductor;

b) The main earthing terminal or main earthing conductor;

c) Pipes within the building such as gas pipes, water pipes;

d) Metallic structural parts, central heating and air conditioning systems, if present.

3.2 Supplementary Equal Potential Bonding Loop

If automatic disconnection of the power supply cannot be achieved in an electrical installation or part thereof, a supplementary equal potential bonding loop must be provided at the location.

The supplementary equal potential bonding loop must include all simultaneously accessible electrically conductive elements, including fixed equipment casings, metallic parts including reinforcing steel in concrete, where possible. The supplementary equal potential bonding loop must be connected to the protective conductor of all equipment, including sockets if present.

Note:

- Using a supplementary equal potential bonding loop does not eliminate the requirement for disconnection of the power supply for other reasons, such as fire protection, overheating in equipment...

- A supplementary equal potential bonding loop may include the entire structure, a part of the structure, or a piece of equipment, a position.

3.3 Where the effectiveness of the supplementary equal potential bonding loop is suspected, it must be confirmed that the resistance R between any equipment casing and any simultaneously accessible electrically conductive element must meet the following condition:

Where:

I_awhich is the operating current of the protective device:

For residual current operated devices, 

For overcurrent operated devices, the operating current is 5 seconds.

4. Protection by Double Insulation or Equivalent Insulation

This measure aims to prevent dangerous voltages from appearing on accessible parts of equipment in the event of a failure of the primary insulation.

a) There must be protection by electrical appliances with double insulation or reinforced insulation meeting the standards;

b) Electrical appliances with double insulation or reinforced insulation must be tested and marked according to relevant standards;

c) Additional insulation implemented during installation to enclose equipment with only primary insulation must ensure a safety level equivalent to that of electrical appliances with double insulation or reinforced insulation;

d) Reinforced insulation implemented during installation to enclose bare live parts must ensure a safety level equivalent to that of tested and certified electrical appliances, this applies only to structural parts that do not require double insulation;

e) Working electrical appliances, all conductive parts isolated from each other by primary insulation, must be enclosed in an insulating casing with at least IP2X protection level;

f) The insulating casing must withstand mechanical, electrical, and thermal stresses that may occur;

g) The insulating casing must not allow electrically conductive parts to pass through and transmit potential. The insulating casing must not contain screws made of insulating material because replacing them with metal screws could damage the insulating properties of the casing;

h) If the insulating casing has a lid that can be opened without tools or locks, then all accessible conductive parts when the door is open must be placed behind an insulating barrier with at least IP2X protection level to prevent accidental contact with these parts. This insulating barrier can only be removed using tools.

PART II

PROTECTION AGAINST THERMAL EFFECTS

Article 14. General Requirements

People, fixed equipment, and fixed tools placed next to electrical equipment must be protected against harmful consequences caused by heat from the electrical equipment, or by thermal radiation such as:

a) Fire, damage;

b) Risk of burns;

c) Affecting the safe operation of the equipment.

Remarks:This section does not address overcurrent protection.

Article 15. Protection Against Fire

1. Electrical equipment shall not cause fire hazards to nearby devices or objects. In addition to the requirements of this standard, the manufacturer's requirements for the equipment must also be met.

2. For equipment with surface temperatures that may pose a fire hazard to adjacent materials, such equipment must:

a) Be mounted on a base or within a casing made of materials capable of withstanding that temperature and having low thermal conductivity, or;

b) Be isolated from other elements using materials capable of withstanding that temperature and having low thermal conductivity;

c) Be installed at a sufficient distance from surrounding objects to allow safe dissipation of heat without causing damage to the materials of those objects. The mounting supports for the equipment must have low electrical conductivity.

3. If during normal operation, the equipment can emit arcs or sparks, then it must:

a) Be fully enclosed in arc-resistant material; or

b) Be isolated from elements that could be damaged by arcs using arc-resistant material, or

c) Be installed at a sufficient distance to ensure safety from arcs for parts that could be damaged by arcs.

Arc-resistant materials used for this purpose must be non-combustible, have low thermal conductivity, and ensure mechanical durability.

The fire resistance level of materials is specified by the competent authority (refer to Appendix 2).

4. Fixed equipment capable of concentrating heat must be placed at a sufficient distance from other objects so that under normal operating conditions, it cannot cause dangerous temperatures for those objects.

Article 16. Selection of Fire Protection Measures Based on External Conditions

1. Protective measures must be selected based on the emergency evacuation conditions (KV1 low density, difficult evacuation; KV2 high density, easy evacuation; KV3 high density, difficult evacuation).

Wiring systems following the evacuation route shall not be within reach unless they are protected against mechanical damage that may occur during evacuation. All wiring systems in the evacuation route should be as short as possible.

2. Under conditions KV2 and KV3, control and protective devices, except those serving for evacuation, must be arranged so that only authorized persons can access them. If these devices are located on walkways, they must be placed in cabinets or sealed boxes made of non-combustible or flame-retardant materials.

3. Under conditions KV2 and KV3, and along the evacuation route, the use of electrical equipment containing flammable liquids is prohibited.

4. Evacuation requirements are specified by the competent authority.

5. Auxiliary capacitors installed in equipment are not subject to this requirement. This exception applies to discharge lamps and motor starting capacitors.

Section III

PROTECTION AGAINST OVERCURRENT

Article 17. General Requirements

Protective devices must disconnect all overcurrents flowing through the conductors before they cause danger due to thermal and mechanical effects or due to excessively high temperatures causing insulation damage, joint damage, terminal damage, or damage to the surrounding environment.

Article 18. Overload Protection

1. Coordination between conductors and overcurrent protective devices

The operating characteristics of overcurrent protective devices must satisfy the following two conditions:

where:

I_B: is the design current used in the conductor;

I_Z: is the continuous current allowed to flow in the conductor;

I_n: is the rated current of the protective device.

For adjustable protective devices, the rated current In is the current chosen when setting.

I₂: is the current ensuring effective operation of the protective device within the agreed time. Current I₂: ensuring effective operation of the protective device is provided in the product standard or may be supplied by the manufacturer.

Protection according to this provision is not fully ensured in some cases, such as small overcurrents lasting longer, and does not necessarily lead to the most economical solution. Therefore, it must be assumed that the circuit has been designed with the condition that small, prolonged overcurrents will not occur.₂  2. Location of overcurrent protective devices

Overcurrent protective devices must be located where changes occur that reduce the allowable current, such as changes in cross-sectional area, type of conductor, and installation method.

3. Cases where overcurrent protection is not installed for safety reasons

Overcurrent protective devices shall not be installed for circuits supplying electrical equipment where circuit interruption may cause danger (such as circuits supplying electromagnetic cranes, excitation circuits for rotating machines, secondary circuits of current transformers). In such cases, warning signals must be issued when there is an overload.

1. Determination of calculated short-circuit current

Article 19. Short Circuit Protection

Calculated short-circuit current must be determined at each relevant point of the equipment system. It can be determined by calculation or measurement.

2. Location of short-circuit protective devices

Short-circuit protective devices must be located where the conductor cross-sectional area decreases or any other change causes a change in the allowable current in the conductor.

The protective device may be located ahead of the place where the cross-sectional area changes or any other change occurs, provided that it has operational characteristics similar to being located behind.

3. Exemption from short-circuit protective devices

Short-circuit protective devices may be exempted in the following cases:

a) Conductors connecting generators, transformers, rectifiers, battery banks to associated switchboards, where protective devices are installed on these switchboards;

b) Circuits whose interruption would endanger the operation of the equipment;

c) Certain measuring circuits.

Provided that both of the following conditions are satisfied simultaneously:

Conductors have been treated to minimize the risk of short circuits.

Conductors are not placed near flammable materials.

4. Protection of parallel conductors against short circuits

4. Short-circuit protection for parallel conductors

A protective device may protect against short circuits in multiple parallel conductors provided that the operational characteristics of such protective device ensure effective action when a fault occurs at the most dangerous point in any conductor. The distribution of short-circuit current among parallel conductors must be considered. A fault point may be supplied from both ends of a parallel conductor.

If a protective device does not provide sufficient protection, one or more of the following measures may be used:

a) A single protective device may be used if:

- The system of conductors has been installed to minimize the risk of short circuits in any conductor, for example, by mechanical damage protection and;

- The conductors are not placed near flammable materials.

b) For two parallel conductors, a short-circuit protective device must be used at the input of each conductor;

c) For more than two parallel conductors, short-circuit protective devices must be placed at both supply and load ends of each conductor.

5. Characteristics of Short-Circuit Protective Devices

All short-circuit protective devices must meet the following two conditions:

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

- A lower breaking capacity is allowed if it is located before another protective device with sufficient breaking capacity. In this case, the characteristics of the devices must be coordinated so that the energy through both devices does not exceed their endurance capability and does not damage the downstream protective device and the conductor protected by it; 

- In some cases, additional characteristics of the downstream protective device, such as electrodynamic force and arc energy, must also be considered. Detailed information should be referred to the equipment manufacturer.

b) All currents caused by short circuits at any point in the circuit must be interrupted before the conductor reaches its limiting temperature.

Article 20. Coordination Between Overload and Short Circuit Protection

1. Protection by a Single Device

When overcurrent protection with a breaking capacity greater than the calculated short-circuit current at the device location is provided, it is considered to offer short-circuit protection for the conductors downstream of that point.

2. Protection by Two Separate Devices

Corresponding requirements apply to the overcurrent protective device and the short-circuit protective device.

The characteristics of these devices must be coordinated so that the energy through the short-circuit protective device does not exceed the endurance capability of the overcurrent protective device.

Article 21. Limiting Overcurrent Through Source Characteristics

Conductors are considered protected against overcurrent and short circuits when they are supplied from a source incapable of supplying a current exceeding the conductor's carrying capacity (for example, isolated transformers, welding transformers, and certain generator sets).

Chapter IV

PROTECTION AGAINST OVERVOLTAGE AND ELECTROMAGNETIC INTERFERENCE

Article 22. General Provisions

The electrical equipment system must ensure safety for people and low-voltage equipment when a fault occurs between the high-voltage system and ground at the high-voltage part of the substation supplying the low-voltage system.

Article 23. Protection of Low Voltage Equipment Against Temporary Overvoltages and High Voltage Earth Faults

Low-voltage equipment must be protected against temporary overvoltages and faults between high voltage and ground.

1. General requirements

When calculating temporary overvoltages, the following states must be considered:

a) Fault between the high-voltage system and ground

b) Loss of neutral

c) Ground fault in the low-voltage system

d) Short circuit in the low-voltage system.

2. Fault Voltage:

a) Fault Voltage

Electrical equipment must withstand temporary overvoltages that may occur.

b) Induced Voltage

The value and duration of the industrial frequency induced voltage of low-voltage equipment during a high-voltage system ground fault must not exceed the values specified in Appendix Table 1.

3. Grounding System in Distribution Substations

In a distribution substation, in addition to the working ground and protective ground, there must be a safe grounding circuit connected to:

a) The ground terminal;

b) The transformer casing;

c) The metal casing of high-voltage cables;

d) The metal casing of low-voltage cables unless the neutral is grounded through a separate ground terminal;

e) The high-voltage grounding wire;

g) The casings of high and low-voltage equipment;

h) Exposed conductive parts.

4. Protection Against Atmospheric Overvoltage and Switching Overvoltage

The electrical equipment system must be protected against transient overvoltages transmitted from the distribution network due to natural causes and against overvoltages generated by operations within the network.

The potential overvoltages at the input of the electrical equipment system, lightning levels, and positions and characteristics of overvoltage protection devices must be considered to reduce the likelihood of overvoltage stress to an acceptable level for the safety of people and property, as well as to ensure continuous power supply.

Article 24. General Requirements for Protection Against Sags

1. When a sag or loss of voltage followed by recovery may cause hazardous conditions for people and equipment, preventive measures must be taken.

Attention must be paid to partial damage to the electrical equipment system or equipment caused by sags.

An overvoltage protection device is not required if the damage to the electrical equipment system or equipment is considered an acceptable risk, provided there is no danger to people.

2. The delay time of the overvoltage protection device must be considered if it could pose a danger to people and equipment.

3. When using a motor starter, the delay time during opening and reclosing must not interfere with immediate circuit interruption by control or protective devices.

4. The characteristics of overvoltage protection devices must comply with the requirements for starting and operating equipment.

5. If the reclosing of a protective device capable of causing a hazardous condition, automatic reclosing must not be permitted.

Chapter IV:

SELECTION AND INSTALLATION OF ELECTRICAL EQUIPMENT

Section I

GENERAL RULES

Article 25. General Requirements for Electrical Equipment

Equipment must comply with Vietnamese standards. If Vietnam does not have such standards, international standards may be used upon recognition by the competent authority.

Article 26. Operating Conditions and External Influences

1. Operating Conditions

a) Regarding voltage

Equipment must have operating voltages compatible with the rated voltage of the power supply.

For some equipment, attention must be paid to the highest or lowest voltage that may occur during normal operation.

b) Regarding current

Equipment must be selected based on the long-term continuous current conditions during normal operation.

Equipment must be capable of carrying currents under abnormal conditions for the duration specified according to the protective device characteristics.

c) Regarding frequency

The rated frequency of the equipment must correspond to the frequency of the power supply.

d) Regarding power

Equipment selected based on power characteristics must be suitable for normal operating conditions taking into account the simultaneous factor.

e) Compatibility

Equipment must be selected so as not to cause harmful effects on other equipment or the power supply during normal operation, including switching operations.

2. External Influences

a) Equipment must be selected and installed according to the requirements of Appendix Table 2, which lists the necessary equipment characteristics corresponding to external influences.

The characteristics of the equipment are determined either by protection levels or by meeting test requirements.

b) A manufactured device without characteristics suitable for external influences at the installation site may still be used if appropriate supplementary protections are anticipated and installed. These supplementary protections shall not impair the operating conditions of the equipment being protected.

c) When different external influences occur simultaneously, their impacts may be independent or interrelated, requiring appropriate protection levels.

Article 27. Accessibility

All equipment must be arranged to facilitate operation, inspection, and maintenance.

Article 28. Marking and Identification

1. General Requirements

Equipment must have labels or identification methods to distinguish the tasks and parameters of switching devices and testing devices.

2. Electrical Conductor Systems

Electrical conductor systems must be arranged and marked to allow identification for inspection, testing, and repair.

3. Identification of Neutral Wires and Protective Wires

Measures must be taken to distinguish neutral wires from protective wires.

4. Protective Devices

Protective devices must be arranged to easily distinguish the circuits they protect.

Article 29. Prevention of Harmful Mutual Interference

1. Harmful Effects

Equipment must be selected and installed to prevent any harmful effects between equipment, including non-electrical equipment.

2. Electromagnetic Influence

Electrical equipment must be chosen based on its ability to withstand electromagnetic interference and must not generate electromagnetic interference that adversely affects related equipment.

The interference resistance level of the equipment must consider electromagnetic influences during long-term operation.

PART II

ELECTRICAL CONDUCTOR SYSTEM

Article 30. General Requirements

The electrical conductor system must be selected to be suitable for the electrical equipment.

Article 31. Pre-Made Busway Systems

The busbar system must be installed according to the product standards and the manufacturer's instructions.

Article 32. Selection and Installation Considering External Influences

When installing, the following impacts must be considered:

1. Ambient temperature

The electrical conductor system must be selected and installed to be compatible with the highest ambient temperature.

2. In the presence of water

The electrical conductor systems must be selected and installed so as not to be damaged in wet conditions.

3. In the presence of solid objects, plant and animal intrusions

The electrical conductor system must be selected and installed to minimize risks from solid objects and plant and animal intrusions.

4. In environments containing corrosive or polluting substances

In conditions with corrosive or polluting substances, the electrical conductor system must be selected or have measures to enhance protection against corrosion.

5. Subject to mechanical effects

The electrical conductor system must be selected and installed to minimize damage due to mechanical stress during normal operation such as impact, vibration, penetration, or compression.

6. Building structures

When building structures pose risks of movement (settlement joints, expansion, etc.), cable supports and protective systems must allow relative movement to prevent conductors and cables from enduring excessive mechanical stress.

7. In the presence of solar radiation

The electrical conductor system must be selected to withstand the effects of solar radiation or appropriate protective measures must be taken.

Article 33. Current Carrying Capacity

The electrical conductor system must be selected based on the largest current running through the conductor under normal operating conditions, ensuring that the conductor temperature increase does not exceed the permissible limit (refer to Appendix 3).

Article 34. Conductor Cross-Section

1. The cross-sectional area of the conductor is chosen based on mechanical conditions, voltage, and heating conditions, without considering motor startup times or increased currents from certain equipment.

2. The neutral conductor in a single-phase two-wire circuit must have the same cross-sectional area as the phase conductor.

c) Providing technical assistance to provinces and centrally administered cities under their jurisdiction in developing local technical standards on clean water quality.In multi-phase circuits where phase conductors have a cross-sectional area greater than 16 mm²square of copper or 25 mm²square of aluminum, the neutral conductor may have a smaller cross-sectional area than the phase conductors if the following conditions are met simultaneously:

a) The maximum current in the neutral conductor during normal operation, including harmonics if present, does not exceed the allowable current corresponding to the reduced cross-sectional area of the neutral conductor;

b) The minimum conductor cross-section (see Appendix 4).

Article 35. Electrical Connections

1. Connections between conductors and between conductors and other devices must ensure continuous long-term electrical operation, mechanical durability, and appropriate levels of protection.

2. All connections must be accessible for inspection, testing, and maintenance, except in the following cases:

a) Connections of buried cables;

b) Connections enclosed in synthetic materials or sealed.

3. When connecting two conductors made of different materials at the connection point, measures must be taken to protect the conductor or conductor with lower heat resistance and to protect against corrosion.

Article 36. Selection and Installation of Electrical Conductors to Limit Fire Spread Within Buildings

1. Suitable materials must be selected and installed according to external conditions to minimize fire spread risks.

2. The conductor system must be installed so as not to reduce the structural and fire safety characteristics of the building.

3. Cables and products meeting fire-resistant standards can be installed without special measures.

Article 37. Selection and Installation for Maintenance and Cleaning

When installing the conductor system, it must facilitate operation and maintenance processes.

Section III

||| DISCONNECTING AND CONTROL EQUIPMENT

Article 38. General Requirements

1. The moving contacts of all multi-pole devices must be mechanically connected such that they close and open simultaneously, except for neutral wire contacts which may close before and open after other contacts.

2. In multi-phase electrical circuits, single-pole devices shall not be installed on the neutral wire, except for devices such as isolators, sockets, plugs, and replacement parts in fuses.

Article 39. Equipment for Indirect Contact Protection by Disconnecting the Power Supply

1. Maximum current protective devices

When a fault or overload occurs, there must be a maximum current protective device to disconnect the power supply from the fault.

2. Overcurrent protective devices (imbalance current protective devices)

a) Imbalance current protective devices must ensure the disconnection of all conductors carrying current in the protected circuit section;

b) Imbalance current protective devices must be arranged so as to only disconnect imbalance currents, not disconnecting power when stray currents appear under normal operating conditions;

c) Using imbalance current protective devices in combination with circuits without protective conductors, even if the rated imbalance current does not exceed 30 mA, shall not be considered a complete protection against indirect contact.

Article 40. Equipment for Overcurrent Protection

1. General requirements

a) Screw-type fuse bases must be connected such that the contact point is connected to the power supply conductor.

c) Plug-type fuse bases must be arranged such that the fuse cover cannot come into contact with the conductive parts of adjacent fuse bases.

d) When electrical switches can be operated by untrained personnel, they must be designed or installed such that the adjustment values of overcurrent protective devices cannot be changed without a key or tool, and there must be a visible indicator showing the adjustment value.

2. Selection of overload protective devices for conductors

The rated current (or setting current) of the protective device must be selected appropriately according to the following conditions:

where:

IB : is the design current used in the conductor;

Iz   : is the continuous current allowed to flow in the conductor;

In   : is the rated current of the protective device.

For adjustable protective devices, the rated current In is the selected current when adjusted.

I₂  is the current ensuring effective operation within the specified time of the protective device. The current I₂: ensuring effective operation of the protective device is provided in the product standard or may be supplied by the manufacturer.

3. Selection of short-circuit protective devices for conductors

The application of overcurrent protection rules for short circuits with a maximum duration of 5 seconds must take into account the maximum short-circuit conditions.

When the protective device specifies both the ability to cut off rated short circuits during operation and the ability to cut off maximum rated short circuits, the protective device can be chosen based on the ability to cut off short circuits under maximum short-circuit conditions. However, when selecting the protective device, the short-circuit conditions that may occur during operation must be taken into account. The protective device is installed at the power supply side of the installation.

Article 41. Equipment for Overvoltage and Electromagnetic Interference Protection

1. Overvoltage protection devices

Lightning protection devices must be selected and installed for buildings to limit overvoltages caused by lightning from the distribution system and to protect against overvoltages caused by switching operations within the installation.

2. Installation requirements for lightning protection

Lightning protection devices must be placed as close as possible to the entry point of the equipment system.

Lightning protection must be installed according to the manufacturer's instructions to avoid fire and explosion risks.

Indirect contact protection must still maintain its effectiveness in equipment systems for buildings even when lightning protection fails.

Lightning protection devices and subsequent protective measures must withstand temporary internal overvoltages.

3. Selection of lightning protection devices

Lightning protection devices must comply with equipment standards.

4. Protection against voltage dips

When dangerous voltage dips occur, voltage dip protection devices must be arranged.

Article 42. Isolation equipment and disconnection devices

Isolation and non-automatic switching measures, whether remote or local, must prevent and eliminate dangers to electrical equipment.

1. Isolation

a) Each electrical circuit must be capable of being isolated on each live conductor, except for circuits where protective conductors are required not to be isolated or disconnected;

b) Suitable measures must be taken to prevent accidental energization of equipment, such as locking out, using warning signs, placing within reach of locks or enclosures;

c) Additional measures such as short-circuiting or earthing may be used;

d) When an apparatus or compartment containing live parts is connected to multiple power sources, warning signs or notices must be placed in easily visible locations;

e) Suitable measures must be taken to discharge residual voltages due to induction.

2. Isolating devices

a) Devices performing isolation functions must completely isolate live conductors supplying power from related circuits, taking into account the types of protective conductors that are required not to be isolated or disconnected.

b) Isolating devices must meet the following conditions:

- In the open state, they must withstand impulse voltages between terminals as specified in Appendix 5 table, depending on the rated voltage of the equipment system.

- A greater distance may be required than the corresponding distance for impulse voltage withstand if other tasks beyond the isolation function are considered.

c) The isolation distance between the open poles of the device must be clearly and reliably indicated by "open" markings. Such indications must only appear when the isolation distance between the open contacts of each pole has been achieved.

d) Semiconductor devices shall not be used as isolating devices;

e) Isolating devices must be designed and/or installed such that they cannot be closed accidentally or randomly (such accidental or random closing could be caused by human action or strong vibrations or impacts).

g) It must be ensured that isolating devices cannot disconnect load currents when the circuit is loaded.

h) In the case of multi-pole switches, isolating devices with the corresponding number of poles or suitable disconnecting means must be used.

i) All devices used for isolation must be clearly identified to indicate the circuits that are isolated.

3. Circuit breaking for maintenance

a) Power must be disconnected when maintenance work poses a danger.

b) Must have appropriate measures to prevent electrical equipment from being inadvertently energized during maintenance, such as locking out, posting warning signs, etc.

c) Equipment for disconnecting power during maintenance;

d) Equipment for disconnecting power during maintenance must be placed on the power supply circuit;

e) Equipment for disconnecting power during mechanical inspection or maintenance, or for controlling auxiliary circuits, must be controlled solely by human intervention, completely eliminating automatic, interlocked, or remote control circuits;

g) Equipment for mechanical maintenance must be designed and/or installed to avoid accidental or random re-energization;

h) Equipment for disconnecting power during mechanical maintenance must be arranged and marked so as to be easily recognizable and convenient to use.

4. Emergency operations

4.1 General requirements

Emergency operations may be for emergency start-up or emergency shutdown.

a) There must be emergency disconnection means for all parts of the equipment where it may be necessary to control the supply of electricity to eliminate unexpected hazards;

b) In cases of electric shock risk, emergency disconnection devices must cut off all live wires except protective conductors that do not require isolation;

c) Emergency switching means, including emergency stop, must act directly on the power supply sources;

d) They must be arranged so that a single action can disconnect the correct power supply source;

e) Emergency disconnection devices must be arranged so that operation does not cause further danger or complicate the resolution of hazards;

g) There must be emergency stopping means when movements caused by electricity could be dangerous, such as escalators, elevators, conveyors, etc.;

4.2 Emergency disconnection devices

a) Emergency disconnection devices must be able to disconnect the load current of related equipment sections taking into account the motor braking current;

b) Emergency disconnection means may be:

- A device capable of directly disconnecting the power supply, or

- A combination of devices activated by a single action aimed at disconnecting the power supply;

c) During emergency stoppage, it may be necessary to maintain power supply, for example, to brake moving parts;

d) Hand-operated devices (handles, push buttons, etc.) for emergency disconnection must be clearly identifiable, painted red against a suitable contrasting background;

e) Operating means must be easily accessible at locations where danger may occur and at appropriate locations to eliminate danger from a distance;

g) Operating means for emergency devices must be lockable in the "disconnect" or "stop" position unless both emergency disconnection and re-energization means are under human supervision;

After releasing an emergency disconnection device, power must not be reapplied to the equipment;

h) Emergency disconnection devices, including emergency stop devices, must be placed and marked so as to be easily recognizable and convenient for operation.

5. Functional switching (control)

5.1 General requirements

a) There must be functional switching devices for each section of the circuit requiring independent control from other parts of the equipment;

b) Functional switching devices do not necessarily need to disconnect all live wires of the circuit;

Single-pole control devices must not be installed on neutral wires;

c) Sockets and plugs with rated currents less than 16 A may be used for switching functions. When used, polarity must be noted;

d) Control devices for functional switching intended to change power sources must affect all live conductors and must not place sources in parallel, unless the equipment has been designed for this condition;

5.2 Functional switching devices

a) Functional control switching devices must be suitable for the heaviest possible operating conditions;

b) Functional control switching devices may disconnect the current without opening corresponding poles (for example, semiconductor control devices);

Functional control switching devices may include:

- Load switches;

- Semiconductor devices;

- Circuit breakers;

- Motor starters;

- Plugs and sockets below 16 A;

c) Isolating switches, fuses, and busbars must not be used as functional control devices;

5.3 Control circuits

Control circuits must be designed, arranged, and protected to minimize any dangers arising from faults between control circuits and other conductive parts that may affect the operation of controlled equipment;

5.4 Motor control

a) Motor control circuits must be designed to prevent motors from automatically restarting after voltage sag or loss if such restart could be hazardous;

b) If the motor uses electrical braking, there must be measures to prevent reverse rotation upon completion of the braking process if such reverse rotation is hazardous;

c) If safety depends on the direction of motor rotation, there must be measures to prevent reverse rotation, for example, due to phase sequence reversal or loss of a phase;

Attention must be paid to the hazards that may arise from a single-phase failure;

Chapter IV

GROUNDING EQUIPMENT AND PROTECTIVE CONDUCTORS

Article 43. General requirements

The grounding resistance of grounded equipment must meet the safety protection requirements and operational requirements of electrical equipment systems;

Article 44. Earthing

1. Grounding equipment

1.1 Grounding equipment used either jointly or separately for protection and operation according to the requirements of the equipment;

1.2 Selection and installation of grounding equipment must ensure:

a) Grounding resistance values that comply with equipment protection and operational requirements and are maintained over time;

b) Fault ground currents and earth leakage currents can pass through without causing danger, especially due to thermal, mechanical, and electromechanical effects;

1.3 Measures must be taken to prevent damage to other metal parts due to electrolytic action;

2. Grounding terminals

2.1 The following types of grounding terminals may be used:

a) Bars, pipes, plates, or wires;

b) Metal electrodes located at the bottom of foundation pits;

c) Reinforcing bars in concrete;

d) Other suitable structures.

2.2. The type and burial depth of the grounding electrodes (poles) shall be such that when the soil is dry and frozen, the grounding electrode (pole) resistance does not exceed the required value.

2.3 Materials used for the structure of grounding electrodes must be resistant to corrosion.

2.4 Conductors from other structures may only be used as grounding electrodes with the agreement of the owner of the structure.

Pipes conveying flammable substances (gas pipes, oil pipelines, etc.) shall not be used as grounding electrodes.

3. Grounding Wires

a) Grounding wires must meet the minimum cross-sectional area requirements, and when buried underground, the cross-sectional area must not be less than the value specified in Appendix 6;

b) The connection of grounding wires to grounding electrodes must be made in such a way as to ensure mechanical durability and electrical conductivity under operational conditions.

When clamps are used, they must not damage the grounding electrode or grounding wire.

4. Grounding Terminal Ends or Main Grounding Bars

In all equipment requiring grounding, there must be grounding terminal ends or main grounding bars to connect to the grounding system.

Grounding terminal ends or main grounding bars must be located in places that are easily accessible for measuring ground resistance.

Article 45. Protective conductors

1. Minimum Cross-Sectional Area

a) The cross-sectional area of the conductor must not be smaller than the value determined by the following formula: (applicable only for cutting times not exceeding 5 seconds)

where:

S: cross-sectional area (mm²);²).

I: maximum fault current value (RMS) that can pass through the protective device (A);

t: operating time of the switching device in seconds (s);

k: coefficient dependent on the material of the protective conductor, insulation, and other parts, and initial and final temperatures. The values of the coefficient k for protective conductors under different conditions are listed in Appendices 7, 8, 9, and 10.

If the calculated cross-sectional area is smaller than the standard value, then a standardized higher cross-sectional area conductor must be used.

The calculated cross-sectional area must comply with the conditions specified for the total loop impedance.

Separate temperature limits apply to equipment in explosive environments.

Maximum allowable temperatures for connections must be considered.

b) The cross-sectional areas of protective conductors must not be smaller than those specified in Appendix 10. In this case, compliance with Article 47 is not required.

If applying this table results in non-standardized values, then a standardized higher cross-sectional area conductor must be used.

The values in Appendix 10 are valid only if the materials of the protective conductors are the same metal as the phase conductors. If this condition is not met, the cross-sectional areas of the protective conductors must be determined to achieve equivalent conductivity as specified in Appendix 10.

c) In all cases, protective conductors that are not part of supply cables or cable sheaths must have a minimum cross-sectional area of:

2.5 mm²²if mechanical protection is provided.

4 mm²if no mechanical protection is provided.

2. Types of Protective Conductors

a) Protective conductors may be:

- Conductors within multi-core cables;

- Insulated or bare conductors within a common sheath with live conductors;

- Separate fixed bare or insulated conductors;

- Metal sheaths, such as cable sheaths, shielding, steel cable sheaths;

- Certain external conductive elements.

b) When equipment has pre-assembled enclosures or metal busbars, the metal enclosures or metal frames may be used as protective conductors if they satisfy both of the following conditions:

- Ensure continuous electrical conductivity, resistant to mechanical, chemical, or electrochemical damage;

- Allow connection to other protective conductors at predetermined points.

c) External conductive elements may be used as protective conductors if they satisfy all four of the following conditions:

- Ensure continuous electrical conductivity either by construction or by suitable joints to protect against mechanical, chemical, and electrochemical damage;

- The minimum conductivity must equal the conductivity when applying Article 47;

- Unless compensatory measures are taken, anti-disconnection measures must be provided;

- These elements must be studied before being used for grounding, and supplementary or corrective measures must be taken if necessary.

Metallic water pipes may be used if approved by the person or authority managing the water system. Gas and fuel pipes may not be used as protective conductors.

3. Ensuring Safety of Protective Conductors

a) Protective conductors must be protected against mechanical, chemical, and electromagnetic forces;

b) Switchgear must not be installed on protective conductors;

c) Exposed conductive parts of equipment must not be used as part of protective conductors for other equipment;

d) Connections of protective conductors must be accessible for inspection and testing, except for connections that are sealed or filled with appropriate filler material.

Article 46. Earthing equipment for protective purposes

Grounding wires and protective conductors for equipment that operates on fault voltage must meet the following conditions:

1. There must be a separate, electrically independent auxiliary grounding electrode (pole), for example, metallic structural elements, metallic pipe conduits, metallic cable sheaths. This requirement is satisfied if the auxiliary grounding electrode (pole) is placed far enough from all other grounded metallic elements.

2. The grounding wire leading to the auxiliary grounding electrode (pole) must be insulated to prevent contact with protective conductors or any exposed conductive parts that may come into contact.

3. Protective conductors may only be connected to the enclosures of electrical equipment where power supply to the equipment will be interrupted when the protective device operates under fault conditions.

Article 47. Earthing equipment for operational purposes

Grounding equipment for operational purposes must be implemented to ensure good operation and allow accurate and reliable operation of the main equipment.

Article 48. Earthing equipment for both protective and operational purposes

When combined protection and operational grounding is required, the requirements for protective measures must take precedence.

Article 49. Equal potential bonding conductors

The minimum cross-sectional area of the equipotential bonding conductor must satisfy the following conditions:

1. Main equipotential bonding conductor

The main equipotential bonding conductor must have a cross-sectional area not less than half the cross-sectional area of the largest protective conductor in the system of equipment and at least 6 mm². However, this cross-sectional area shall not exceed 25 mm²if it is copper or an equivalent cross-sectional area if it is another metal.

2. Supplementary equipotential bonding conductor.

If there is a supplementary equipotential bonding conductor connecting two enclosures of equipment, then the cross-sectional area of the supplementary equipotential bonding conductor may be not less than that of the smaller protective conductor of the two protective conductors connected to those exposed parts.

If the supplementary equipotential bonding conductor connects the enclosures of equipment with an external conductive element, its cross-sectional area shall not be less than half the cross-sectional area of the corresponding protective conductor.

Section V

OTHER EQUIPMENT

Article 50. Low-voltage generator sets (LVGS)

b) In cases where funds from organizations and individuals within and outside Vietnam are used for victim support work and victim support benefits, such activities shall be carried out in accordance with the regulations of the Ministry of Finance and the donor; in cases where there is no agreement between the donor or their authorized representative and the Ministry of Finance regarding the expenditure level, the expenditure level prescribed in this Circular shall apply.

Applies to low-voltage power generation systems accompanying generators intended to provide continuous or intermittent supply to all or part of the equipment system or to mobile equipment not permanently connected to a fixed equipment system. Low-voltage generator equipment may include components such as: Internal combustion engines, Turbines, Electric motors, Solar panels, Batteries, Other sources...

Applies to synchronous generators with main excitation or independent excitation, asynchronous generators with excitation or self-excitation, converters.

Applies to the following types of supply:

a) Supplying an equipment system not connected to the public distribution network;

b) Supplying an equipment system, replacing the public distribution network;

c) Supplying an equipment system in parallel with a public distribution network;

d) Combination of the above types.

2. General requirements

a) Excitation measures and switching must be appropriate for the purpose of the generator equipment; safety and individual functions of different types of sources shall not be affected by this generator equipment;

b) Expected short-circuit currents and earth fault currents must be considered for each type of supply source or for each combination of sources that can operate independently or in conjunction with other sources. Short-circuit protection devices within the equipment system, connected to the public network, must withstand during all modes of operation of the sources;

c) When the generator equipment only supplies an equipment system not connected to the public distribution network, the capability and operational characteristics of this generator equipment shall not pose danger or damage to the equipment after connection or disconnection due to deviations from specified voltage and frequency levels. Measures must be taken to automatically disconnect part of the equipment system when necessary if the generator set is overloaded.

Note:

- Starting current factor of large loads must be taken into account.

- Attention must be paid to the power factor specified for protective devices.

- Installing generator equipment inside an existing building may change environmental conditions, for example, introducing moving parts, high temperature areas, or toxic gases.

3. Protection against direct contact with power sources or power source combinations

Measures must be taken to prevent direct contact or to interrupt the circuit from the power supply when a person comes into direct contact with live conductors or live equipment.

4. Protection against indirect contact with power supply or power supply combinations

There must be protection against indirect contact in the equipment system for power supply or power supply combinations that can operate independently of other sources.

4.1 Protection by automatic disconnection from the power supply.

Automatic disconnection of the power supply must occur when there is a risk of harmful contact voltage affecting the human body.

This protective measure must be coordinated between grounding system configurations and the characteristics of protective conductors and protective devices.

a) Disconnection

Protective devices must automatically disconnect the power supply so that when there is an insulation failure between a live part and the equipment enclosure or a protective conductor, the contact voltage value exceeding 50V shall not exist for a time sufficient to cause harmful effects on people. In some cases depending on the type of grounding configuration, the maximum allowable disconnection time may be up to 5 seconds.

Note: The term "equipment enclosure" used here refers to the conductive enclosure or mounting frame of the equipment.

b) Grounding

Equipment enclosures must be connected to protective conductors according to the conditions specified for grounding configurations with protective conductors.

Equipment enclosures that can be simultaneously approached must also be connected to a separate, group, or overall grounding device.

Low-voltage generators must have their own operating grounding system and shall not be connected to the public grounding system.

4.2 Additional requirements for equipment systems accompanied by static rectifiers.

a) When protection against indirect contact for parts of the equipment system supplied from a static rectifier relies on automatic switching and protective device operation towards the load not being within the time required by automatic power supply disconnection protection, there must be an equipotential bonding ring between simultaneously accessible conductive exposed parts and conductive exposed parts from outside behind the static rectifier consistent with the supplementary equipotential bonding ring.

The resistance of the supplementary equipotential bonding ring conductors between simultaneously accessible conductive parts must meet the following conditions:

where

I_a: is the maximum earth fault current that the rectifier can provide alone within a maximum time of 5 seconds.

b) Measures or selection of equipment must be made so that protective devices function correctly, damage caused by inverters or filters is avoided.

5. Overcurrent protection for MFĐ

5. Overcurrent protection for MFDS

5.1 For equipment systems where the generator replaces the distribution network, isolation devices must be provided so that the generator cannot operate in parallel with the public supply (including neutral wires).

a) When selecting and using parallel-running power generators with the public distribution network, it is necessary to pay attention to avoid adverse effects on the supply network and other systems in terms of power factor, voltage fluctuation, harmonic waves, imbalance, starting, synchronization, and voltage surges;

b) There must be protection measures to disconnect the generator from the public source in cases of loss of this source or when the voltage or frequency deviation at the supply point exceeds the specified values;

The type of protection, sensitivity, and response time depend on the protection of the source and must be agreed upon with the public source operation management authority;

c) Measures must be taken to prevent connecting the generator to the public source when the public source's voltage and frequency are outside the permissible operating limits;

d) Measures must be taken to isolate the generator from the public source. These isolation measures must be easily accessible by the public source operation manager at all times;

Article 51. Safety equipment

1. General Requirements

Safety equipment must be selected and installed in accordance with the requirements of the load;

This includes general requirements for safety service operations, selection and installation of systems supplying safety services and safe sources. Standby power supply systems are not covered by this provision. This also does not apply to installations placed in hazardous areas;

2. For safety equipment operating under fire conditions, the following must be observed:

a) The safety supply source must be chosen based on the duration of power supply that meets the load's requirements;

b) Equipment, whether manufactured or installed, must withstand fire for the specified period;

3. Equipment arrangement

Equipment must be arranged to facilitate inspection, monitoring, testing, and maintenance;

4. Safe sources

a) Safe sources serving safety services such as fixed equipment must be installed so as not to cause adverse consequences when the safe source fails;

b) Safe sources serving safety tasks must be installed in appropriate and easily accessible locations for skilled personnel;

c) The location of safe sources must be clean and well-ventilated to prevent toxic gases and smoke from safe sources from entering the workplace;

d) Independent branches directly from the public source are not allowed unless it is ensured that two supply sources will not fail simultaneously;

5. Functional circuits

a) Circuits serving safety operations must be independent of other circuits;

b) Circuits for safety operations shall not pass through areas at risk of fire unless they can withstand fire. In any case, circuits shall not pass through high-risk explosion zones;

c) Circuit breakers, switches, except alarm devices, must be clearly identified and grouped in places accessible only by skilled personnel. Alarm devices must also be clearly marked;

6. Use of equipment

a) In lighting systems, lamps must be suitable for maintaining the required light level during interruptions;

b) In equipment supplied by two different circuits, a fault in one circuit must not damage the ground fault protection or the accurate operation of the other circuit. Such equipment must be connected to the protective conductors of both circuits if necessary;

c) Ground fault and short-circuit protection must be ensured in the event of a fault for each source;

d) Ground fault and short-circuit protection must be ensured in the event of a fault, even if the equipment is supplied separately by two sources or both operate in parallel.

Article 52. Lighting equipment for safety services

1. Objective

This provision is for selecting and installing lamps and lighting equipment belonging to the fixed equipment system.

The requirements of this provision do not apply to temporary lighting systems.

2. General Requirements

Lamps must be selected and installed according to the manufacturer's instructions and general regulations.

3. Protection against Thermal Effects

a) To select lamps regarding thermal effects on the surrounding environment, the following points should be considered:

- The maximum allowable energy emitted from the lamp panels;

- The heat resistance of surrounding objects at the installation point and in areas affected by temperature.

Minimum distance from flammable materials.

b) Depending on the fire resistance of materials at the installation site and in areas affected by heat, manufacturers' guidelines must be followed. Lamps must be selected and installed according to general regulations.

4. Wiring Systems

a) If suspended lamps are used, the suspension part must withstand a load five times the weight of the lamp. Cables and conductors between the suspension part and the lamp must be installed without tension or torsion stress at the connection points;

b) When insulated cables and conductors pass through lamps during installation, suitable conductors and cables as specified must be chosen, and only lamps designed for cable passage should be used.

5. Protection against Electric Shock for Lamp Fixtures

There must be protection against electric shock by:

a) Using a safe supply voltage, or;

b) Using a residual current device that automatically cuts off power supply with a rated residual current value not exceeding 30 mA;

c) Other measures.

 

APPENDIX TABLE

Appendix 1: Permissible alternating voltage stress

 Appendix 2: External conditions

 

Appendix 3: Maximum operating temperature with different types of insulation

 Appendix 4 Minimum cross-sectional area of conductors

 Appendix 5: Surge withstand voltage according to rated voltage

 Appendix 6: Prescribed cross-sections of earth conductors

 Appendix 7: Values of k for insulated protective conductors not directly associated with Cables or bare protective conductors contacting cable sheaths

 Appendix 8: Values of k for single-core protective conductors within multi-core cables

Appendix 9: Values of k for bare conductors where there is no risk of damage to adjacent materials due to heat generated

 Appendix 10 Minimum cross-sectional area of protective conductors