Surge Protection
Everything in your home that’s worth money now has a circuit board in it — your inverter, your battery, your oven. All of it runs on a supply that occasionally spikes to thousands of volts for a few millionths of a second.
Surge protection is the device that stands between the two. Here’s what it does, which type your home needs, where it goes on a solar system, and why it quietly vanishes from cheap quotes.
What does a Surge Protection Device do?
A Surge Protection Device is essentially a pressure release valve for electricity.
Inside is a component that behaves like an open switch at normal voltage — power flows past and nothing happens. The moment voltage spikes above a set threshold it turns conductive in nanoseconds and diverts the excess energy straight to earth, before it reaches your inverter, your battery or your telly. Once the spike has passed, it goes back to doing nothing.
There’s also a DC SPD, specific to solar and rated for the much higher DC voltages your array runs at. An AC device won’t do that job — which is exactly the kind of substitution we find on other people’s installs.
Where surge protection goes?
A properly protected system has surge protection on both sides of the inverter
- On the DC side: between the array and the inverter — protecting the inverter from anything the roof picks up.
- On the AC side: between the inverter and your consumer unit — protecting the inverter from whatever the grid throws at it, and protecting the rest of the house from the inverter’s circuit.
Distance matters too. If the run between an SPD and the equipment it’s protecting is much longer than 10 metres, the protection starts losing its effect and a second device is needed closer to the kit. On a typical house the inverter is in the loft or garage and the consumer unit is downstairs — so that 10 metres goes quicker than you’d think. It’s a detail that gets skipped a lot.
