Overvoltages (surges) may have atmospheric causes (lightning) or may be a result of switching or starting of high-powered industrial equipment in the proximity.
Overvoltages can spread through both the power supply and earthing systems, potentially destroying sensitive equipment.
Transient overvoltages cause the premature ageing of equipment connected to the electricity network and may even destroy it if the surge is large enough.
Appliances such as televisions, computers, smoke alarms, fridges, boilers, hi-fi equipment and most other household appliances with electronic controls are all vulnerable to damage from electrical surges.
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Surge Protection Devices (SPDs) limit the overvoltage to a level within the impulse voltage resistance of the protected equipment. They are usually installed within the consumer unit and feature a visible (colour-coded) indication of correct function. Each SPD has a replaceable cartridge which can be renewed when it no longer functions. If required, an SPD can be installed in a separate enclosure in order to retro-fit to an existing installation.
The wiring regulations (BS 7671) require protection to be provided (in all types of premises) where overvoltages could cause:
- Serious injuries to people
- Loss of human life
- Interrupt public services
- Damage cultural heritage
- Interrupt commercial/industrial activities
- Affect a large number of individuals at one location
In all other circumstances, a risk assessment must be conducted to determine whether protection is required. If no risk assessment is carried out, then protection must be provided.
Where the value of the installation and equipment contained within justifies it, overvoltage protection must be provided in a single-unit domestic dwelling.
It is now standard practice to fit a surge protective device (SPD) as part of a consumer unit installation or replacement to provide overvoltage protection and to ensure compliance with the regulations.
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