IEC and BS 7671 Requirements for Consumer Unit and Distribution Board

Electrical Technology

IEC-60364 and BS-7671 Guidelines for Garage Unit, Consumer Unit and Distribution Board

The IEC (International Electrotechnical Commission) and BS 7671 (British Standard for Electrical Installations) both provide essential requirements for electrical installations, including those for fuse boards like garage unit, consumer unit and distribution board. While the IEC 60364 standard outlines international best practices, BS 7671 – 2018 (which is aligned with IEC standards BS EN 61439) specifically applies to the UK. Below are key requirements from both standards related to electrical panels:

Good to Know:

The IEC 60364 “Low-voltage electrical installations” equivalent for EU is HD 60364.
IEC 60364 address residential premises. Refer to IEC 60364-7-701 for special installation and locations e.g. in showers and bathrooms.
One distribution board or consumer unit is enough for one residential premises including the meter.

Location and Accessibility

According to BS 7671: 132.12 and IEC 60364-5-52:

Readily Accessible: Electrical panels must be located in areas that are easily accessible for operation, maintenance, and inspections.
Residential: The recommended height for distribution board and consumer unit is between 1 metre to 1.8 metre from the floor. The suggested height is 1.3 metres for elderly and handicapped people in the residential unit.
Industrial: In an industrial building, a typical distribution board with an IP54 degree of protection requires a mounting area with a maximum width of 1.50 meters, a maximum height of 1.20 meters, and a maximum depth of 0.50 meters. IEC 61439.
Clearance: Adequate working space should be provided around panels. BS 7671 specifies sufficient space for safe access to components.
Switchgear Installation: Switchgear shall be installed outdoors unless it is suitable for indoor installation or enclosed in a cabinet providing a protection degree of at least IP4X, IP5X, or IP6X. (BS 7671: Section 422.3.3)
Double Insulation and Covers: Double insulation and covers shall be used for live parts when metallic distribution boards are installed.
Environmental Conditions: Panels should be installed in areas free from water, excessive dust, and other adverse environmental conditions that could impact safety or performance..

Panel Ratings

According to BS 7671: 536 and IEC 61439:

distribution boards, consumer units and related devices and equipment must be selected according to their current-carrying capacity and the system’s overall load.
IEC 61439 governs the design, testing, and construction of electrical panels (low-voltage switchgear and controlgear assemblies), ensuring panels meet safety and performance standards.
All the protective devices used in the consumer unit for residential and distribution board for commercial and industrial application must be verified by BS EN 61439-3 and comply with IEC – 60898 and IEC 60947-2 in B, C and D curves.
Panel boards must be suitable for the intended environment, with consideration for insulation and temperature ratings.

Isolation and Switching

According to BS 7671: Section 537 and IEC 60364-5-53:

Panels must provide adequate means for isolation and switching, allowing circuits to be disconnected for maintenance or in emergencies.
Main isolators should be clearly labeled and accessible. The isolator must disconnect all live conductors (phase and neutral) simultaneously in cases where isolation is required for safety.
Emergency Disconnect: An interrupting device or emergency disconnect switch shall be installed to disconnect the main power supply in case of an emergency or danger, where immediate interruption of the supply is necessary. (BS 7671: Sections 132.9 and 132.10)

Earthing and Protective Conductors

According to BS 7671: Chapter 54 Section 541 to 544 and IEC 60364-5-54:

Proper earthing (grounding) is required to protect users and equipment from electric shock.
Panels must be equipped with protective earth connections, and proper bonding must ensure that exposed conductive parts do not pose a safety risk.
Equipotential bonding should be in place to prevent dangerous voltages from developing between exposed metalwork.
541.3 – BS 7671 suggest to comply the reference with BS EN 62305 if there is lighting protection system.
PEN conductors shall not be used in hospitals, emergency unit and other medical locations downstream of the main distribution board or consumer unit. 710.312.2 – BS 7671-2028,

Selection of Protective Devices

According to BS 7671: 536.3 and IEC 60364-5-53;

Protective devices in the panel should be coordinated to ensure that in the event of a fault, only the circuit in question is disconnected, rather than the entire system.
This is crucial for maintaining the safety and reliability of installations, particularly in multi-circuit systems.

Overcurrent Protection

According to BS 7671: Chapter 43, Section 420 to 424 and IEC 60364-4-43:

Electrical panels must have appropriate overcurrent protection devices (OCPDs) like fuses or circuit breakers e.g. MCBs, RCD,s RCBOs, AFDDs, and SPDs.
The OCPDs should be rated based on the circuit design to prevent damage to wiring and reduce fire risks.
BS 7671 requires proper coordination between conductors, OCPDs, and protective devices to ensure that conductors are protected against thermal damage.

Short Circuit Protection

According to BS 7671: 434 and IEC 60364-4-43

Protection against short circuits must be provided in the panel, with devices rated to interrupt the maximum fault current that could occur in the system.
Short circuit protection devices should be selected based on fault current levels and should operate quickly to minimize damage.

RCDs, AFFD and Earth Fault Protection

According to BS 7671: 415, 536, and IEC 60364-4-41; Residual Current Device (RCD), Arc Fault Detection Device (AFDD), CBR, RCCB or RCBO (Residual Current Breaker with Overload projection) with OCPD, earth fault projection and surge protective device (SPD) etc. must be used (when applicable) in the distribution board and consumer unit to protect both the device and operator e.g.:

RCDs (Residual Current Devices) are required to provide additional protection against electric shock, especially in circuits supplying socket outlets and equipment in wet or outdoor locations.
30mA High-Sensitivity RCD: A 30mA high-sensitivity RCD must be added to the consumer unit for socket-outlet circuits, circuits feeding bathrooms, and lighting circuits in accordance with IEC 60364.
In the TT System: In the absence of RCD protection in a TT system, double or reinforced insulation shall be provided on all circuits upstream of the first RCD to ensure operator protection.
Earth fault protection must be in place to disconnect the power in case of a fault that could lead to electrocution or equipment damage.
In the TN System: In a TN system, earth fault protection should be provided via a circuit breaker. The protective earth conductor (PE) and exposed conductive parts of all insulated appliances and equipment must be connected to the consumer-installed earth electrode.

Environmental Protection (IP Ratings)

According to BS 7671: 512.2 and IEC 60364-5-52:

Electrical panels must have appropriate IP ratings (Ingress Protection) depending on their installation environment (e.g., indoor, outdoor, dusty, or wet areas).
The IP rating ensures that the enclosure of the panel provides adequate protection against solid objects and liquids entering and damaging the components.
Temperature Limits: Electrical equipment shall be installed in such a way that the design temperature does not exceed its specified limits. (BS 7671: Section 134.1.5)

Segregation of Circuits

According to BS 7671: 514.10 and IEC 60364-5-52

Segregation between different types of circuits, such as power, lighting, or control circuits, must be maintained within the panel to prevent interference or faults.
Cables and components with different voltage ratings should not be installed in the same compartment without adequate insulation or separation.

Cable used in Wiring System

According to BS 7671: Section 422.3.4 Cables used in:

Non-combustible materials shall comply with EN 60332-1-2.
Conduit systems shall comply with BS-EN 61386-1.
Cable trunking and ducting systems shall comply with BS-EN 50085.
Cable tray or ladder systems shall comply with BS-EN 61537.
Power track systems shall meet the flame propagation resistance requirements specified in BS-EN 61534.
Wiring systems with a high risk of flame propagation shall meet the requirements specified in BS-EN 60332-3

Circuit Identification and Labeling

According to BS 7671: 514.1 and IEC 60364-5-51

All circuits within the electrical panel must be clearly labeled to indicate their function and the areas they serve. A suitable indicator complying with BS EN 60073 and BS EN 60447 shall be positioned to clearly visible to the operator.
Information should be provided indicating the high current protective conductor. The information should d be clearly visible to the person who is working or modifying the circuit. BS 7671-2028 – 543.7.1.205.
A single-line diagram, drawing or general schematic diagram having the full details of all electrical safety sources should be given adjacent to the distribution board or consumer unit. 560.7.9 and 560.7.10 – BS 7671-2028.
Color coding of conductors should conform to standards to ensure clarity for electricians and maintenance personnel. For example, the phase (live) conductor is brown, neutral is blue, and protective earth is green/yellow in BS 7671. Some of the British standards and IEC following countries (including UK prior to 2004 before adopting the IEC color codes) is using Red, Black and Green for Phase, Neutral and Earthing conductor. Refer to the IEC and NEC wiring color codes for AC and DC.

Verification and Testing

According to BS 7671: Part 6 and IEC 60364-6:

After installation, electrical panels must be inspected and tested to verify compliance with BS 7671 and IEC standards.
The testing process should confirm the functionality of protective devices, correct wiring, and proper earthing.
Periodic inspections and testing are also required to ensure the ongoing safety of electrical installations.

Both IEC 60364 and BS 7671 aim to ensure safety, reliability, and efficiency in electrical systems. Compliance with these standards helps prevent electrical fires, shock hazards, and equipment damage.