Protection against voltage disturbances and electromagnetic disturbances – Chapter 44

Chapter 44 Protection against voltage disturbances and electromagnetic disturbances

Section 443, which deals with protection against overvoltages of atmospheric origin or due to switching, has been redrafted.

The AQ criteria (conditions of external influence for lightning) for determining if protection against transient overvoltages is needed are no longer included in BS 7671. Instead, protection against transient overvoltages has to be provided where the consequence caused by overvoltage (see Regulation 443.4)

(a) results in serious injury to, or loss of, human life, or
(b) results in interruption of public services/or damage to and cultural heritage, or
(c) results in interruption of commercial or industrial activity, or
(d) affects a large number of co-located individuals.

For all other cases, a risk assessment has to be performed in order to determine if protection against transient overvoltage is required.

There is an exception not to provide protection for single dwelling units in certain situations.