Surge Protection Devices (SPD)


The latest (18th) Edition of The Wiring Regulations makes anSPD compulsory in most commercial, industrial and Domestic Installations where more than one dwelling is involved. In ordinary houses, a Risk Assessment is recommended where the decision is made not to install one when major electrical works are undertaken.

What does it do?

All electrical supplies are subject to occasional voltage spikes. These can last from millionth to thousandths of a second. They can be caused by problems with the supply equipment,  lightning strikes or motors in nearby properties. SPDs eliminate these from your installation by passing the excess voltage to earth.

What harmful effect can a voltage spike cause?

Voltage spikes can damage electronic equipment including computers, LED lights, domestic appliances, boilers, fire and burglar alarms. In fact anything which is plugged in which has electronic components.

Why do I need one now when I didnt need one before? 

Until recently most appliances had no sensitive electronic parts. A washing machine would have a mechanical timer and a few contact switches, similarly with an oven. Old style bulbs have no electronics and items like a TV would have a large wire wound transformer which would not be affected by power surges. Miniaturisation involves the use of more electronics which are more sensitive to voltage spikes.

Are some properties more prone to surges?

Properties served by overhead power lines are far more likely to be affected by lightning, although underground cables can also be affected by nearby lightning strikes.

How much does an SPD cost?

The inclusion of an SPD would add about £70 to the cost of the installation of a new consumer unit. They can be retrofitted to an existing installation, but the cost would be £100-£300 depending on the installation.

A voltage spike can break your oven, boiler or TV which would cost £200-£300 alone – we’ve all suffered boiler PCB breakdowns. Many of these are caused by voltage surges.

Do SPDs need maintenance?

All SPDs have replaceable cartridges. These have a green indicator which will turn red when the cartridge is no longer effective. Many cartridges are supposed to be user replaceable, but in reality, you will probably need an electrician to remove the cover of the consumer unit to be able to grip the unit to pull it out, but its a 10 minute job. The good news is that the cartridges only need to be replaced after dealing with a number of surges, so if they need replacing, they have already saved your electronic equipment from damaging spikes.