The two are often confused, and some sites have one and think they have both. They protect against different things.
Earthing: protection from electrical faults
Earthing connects the metal parts of your installation to the ground. If a live wire touches a metal casing, the fault current flows to earth and your protection device trips, instead of the casing staying live and shocking whoever touches it. Good earthing also gives sensitive equipment a stable reference, which matters for servers, telecoms and medical devices.
Lightning protection: protection from strikes
A lightning protection system catches a strike on the roof and carries it down the outside of the building into the ground. It deals with currents many times larger than any electrical fault, for a fraction of a second.
How they connect
- Both end in the ground, and the standards require the earthing and lightning earths to be bonded together so there is no dangerous voltage difference between them.
- Surge protection sits between the two: it stops the surge from a nearby strike travelling into the building along power and data cables.
- A site with good earthing but no lightning protection is still exposed to direct strikes. A site with lightning protection but poor earthing can make a strike more dangerous, not less.
What "good" looks like
Many sites aim for an earth resistance below 5 Ω; data centres and telecom rooms often call for 1 Ω or less. The only way to know what you have is to test it.
We test existing earthing and lightning systems and report what needs fixing. See our lightning, earthing and surge protection work.