BS 7671: the 18th Edition

With the 18th Edition to the Wiring Regulations not too far off (it’s due to publish 1st July 2018), Section 443 is likely to be significantly revised based on the recently released IEC and CENELEC publications. The exact requirements still have to be agreed by the UK national committee. Presuming the IET follows the IEC and CENELEC standards.

The conditions of external influence for protection against lightning is needed it may no longer be included in BS 7671. Instead, protection against transient overvoltage would have to be provided where the consequence caused by overvoltage affects:

  • human life
  • public services and cultural heritage
  • commercial or industrial activity

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 Surge Protection Device located at the origin of the installation.

Protection against switching overvoltages should still be considered.

Protection against fire

It is recognised that RCDs can reduce the risk 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 . 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.