Selection of surge protective device (SPD)
February 7, 2023
Surge Protective Devices (SPD) are used to protect the electrical installation, which consists of the consumer unit, wiring and accessories, from electrical power surges known as transient overvoltages.
They are also used to protect sensitive electronic equipment connected to the installation, such as computers, televisions, washing machines and safety circuits, such as fire detection systems and emergency lighting. Equipment with sensitive electronic circuitry can be vulnerable to damage by transient overvoltages.
The effects of a surge can result in either instant failure or damage to the equipment only evident over a longer period of time. SPDs are usually installed within the consumer unit to protect the electrical installation but different types of SPD are available to protect the installation from other incoming services, such as telephone lines and cable TV. It is important to remember that protecting the electrical installation alone and not the other services could leave another route for transient voltages to enter the installation.
There are three different types of Surge Protective Devices:
Type 1 SPD installed at the origin, e.g. main distribution board.
Type 2 SPD installed at sub-distribution boards
(Combined Type 1 & 2 SPDs are available and are usually installed in consumer units).
Type 3 SPD installed close to the protected load. They must only be installed as a supplement to Type 2 SPD.
Where multiple devices are required to protect the installation, they must be coordinated to ensure correct operation. Items supplied by different manufacturers should be confirmed for compatibility, the installer and manufacturers of the devices are best placed to provide guidance on this.