18th Edition: What Are The Requirements for Overvoltage Protection?

Dave Enefer, Devices Product Manager at Crabtree, takes a look at the latest requirements for overvoltage protection.

With the introduction of the 18th edition the decision-making process for inclusion of overvoltage protection in electrical installations has changed.

In certain circumstances overvoltage protection is mandatory. For all other situations a risk assessment is necessary However, if there is no risk assessment carried out overvoltage protection must be installed and in single unit dwellings the final decision is made on a value judgement.

Overvoltage protection requirements

Firstly, we must look at the area where protection against overvoltage must be provided. Designers must consider the consequences of overvoltage, and decide which circumstances apply to each type of building/installation under consideration. Overvoltage protection is mandatory where the consequences of overvoltage can result in:

Serious injury to persons or loss of human life (e.g. nursing homes, care facilities, hospitals)
Interruptions to public services (e.g. 999 call centres, communications & transport networks etc)
Damage to cultural heritage (e.g. loss of irreplaceable artefacts records etc)
Interruption to industrial & commercial activity (e.g. banking, online services data centres etc)
Affects a large number of individuals in one location (e.g. high-rise buildings etc)

For housing providers, the last one may be the most relevant. Where the above consequences of overvoltage could occur, protection is a requirement (see Regulation 443.4).

All other applications – carry out a risk assessment

For circumstances other than those explained above a risk assessment must be carried out to determine if protection against transient overvoltage is necessary. The risk assessment calculation is now based upon a formula that uses values that are given in Table 443.1 and on values related to geographical locations shown in fig 44.2, which is a map of the UK. These values are used with figures that are determined by the lengths of supply cables to the origin of the installation to make a calculation.

If the calculated risk level is 1,000 or less, then protection is required. Readers should consult BS7671 for the full details of the risk assessment criteria and equation.