What is BS 7671?
The BS 7671 Wiring Regulations written by the Institution of Engineering and Technology (IET) set out the standards for electrical installations in the UK as well as many other countries. The IET plays a key role in electrical installation standards and safety, and is known for its independent and trusted voice. ST Electrical Northampton work to the BS 7671.
New 18th edition, what’s new?
Protection against overvoltage
Clause 443 is likely to be significantly revised based on the recently published IEC and CENELEC standard. However, the exact requirements will have to be agreed by the UK national committee. Assuming BS 7671 follows the IEC and CENELEC standard the AQ criteria (conditions of external influence for lightning) for determining if protection against transient overvoltage is needed would no longer be included in BS 7671. Instead, protection against transient overvoltage would have to be provided where the consequence caused by overvoltage effects:
human life, e.g. safety services, medical care facilities;
public services and cultural heritage, e.g. loss of public services, IT centres, museums; and
commercial or industrial activity, e.g. hotels, banks, industries, commercial markets, farms.
For all other cases, a risk assessment would have to be performed in order to determine if protection against transient overvoltage is required. If the risk assessment is not performed, the electrical installation would have to be provided with protection against transient overvoltage.
However, an exception not to provide protection is included for single dwelling units where the total economic value of the electrical installation to be protected is less than 5 times the economic value of the SPD located at the origin of the installation.
Protection against switching overvoltages should still be considered.
Protection against fire
Protection against fire resulting from the electrical installation and the use of the electrical installation has been necessary ever since electricity was first introduced into buildings. Chapter 42 contains the requirements for the protection of persons, livestock and property against fire caused by electrical equipment, against burns and overheating and for including precautions where particular risks of fire exist.
It is recognised that RCDs can reduce the likelihood of fires associated with earth faults. However, whilst RCDs can detect earth faults they aren’t able to reduce the risk of electrical fire due to series or parallel arcing between live conductors because there is no leakage current to earth. Also, it is understood that the impedance of a series arc fault reduces the load current, which will keep the current below the tripping threshold of the circuit-breaker and the circuit-breaker may therefore not operate to disconnect the circuit.
For this reason, details will be included in BS 7671:2018 for the installation of arc fault detection devices (AFDDs) to mitigate the risk of fire in final circuits of a fixed installation due to the effect of arc fault currents.
Changes to Section 753
Section 753 has been extended to apply to embedded electric heating systems for surface heating. They also apply to electric heating systems for de-icing or frost prevention or similar applications and cover both indoor and outdoor systems. These include heating systems for walls, ceilings, floors, roofs, drainpipes, gutters, pipes, stairs, roadways and non-hardened compacted areas. Heating systems for industrial and commercial applications complying with IEC 60519 and IEC 62395 are not covered. The IEC standard covers issues such as surface temperatures and refers the reader to the appropriate IEC Guide.