Surge Protection Devices (SPD)
The purpose of a Surge Protection Device (SPD) is to provide protection against over voltage which may occur as a result of a supply fault, internal fault or switching or a lightning strike.
If an over voltage was to occur there is the potential for serious injury to, or loss of, human life, interruption of supply, damage to electrical equipment and the building fabric.
Regulation 443.4 of The 18th Edition Wiring Regulations (BS7671) requires that protection against transient over voltages is provided where there is a risk of:
Serious injury to, or loss of, human life
Interruption of public services
Damage to cultural heritage
Interruption of commercial or industrial activity
Where a large number of individuals at the same location could be affected
A risk assessment should be performed to determine if protection against transient over voltage is required, If a risk assessment is not performed, the electrical installation should be provided with suitable protection against transient over voltages by the installation of an SPD.
The only exception to this is given for single dwellings, whilst there is no requirement for the provisions of an SPD to be fitted in a single dwelling there may be some justification to have one installed, particularly if a large volume of electronic devices are present.