An SPD (surge protective device) is a component installed in electrical panels to protect downstream equipment from voltage spikes caused by lightning or grid switching. It works by presenting a high impedance at normal operating voltages and rapidly dropping to a low impedance when a high voltage transient occurs. This shunts the destructive surge current safely to earth before it damages sensitive electronics.
We need to install a Type 2 SPD at the main distribution board to protect the new server racks.
SPDs degrade over time as they absorb multiple small transients. Most have a mechanical flag that turns from green to red when the internal varistor is spent and requires replacement.
Also heard as
- surge protective device
- surge protector
Do not mix it up with
- Surge arrester: Surge arresters are typically used on medium and high-voltage utility networks, while SPDs are used on low-voltage consumer installations.
Related terms
Surge arrester
Device that clamps transient overvoltages by diverting surge current to earth, then returns to insulating.
Overvoltage category
Class from I to IV ranking equipment by its position in an installation and the surges it must survive.
Earthing
The practice of connecting electrical equipment and systems to the general mass of the earth.