The survey says your house has "no main bonding"... is that dangerous?

I'm on my knees in a cupboard under the stairs, torch gripped in my teeth, running a finger along a green-and-yellow wire. It comes down tidy from the consumer unit, loops behind a row of coats, and ends at a clamp. So far, so good. Then I follow what the clamp is bolted to: a stub of copper about six inches long that disappears straight into a grey plastic stopcock. Past that, out to the street, it's all blue plastic. So that neat bit of bonding is clamped to a dead end. It reaches nothing.

That right there is what a surveyor means when he writes "no adequate main protective bonding" on your report and leaves it at that. Sometimes the clamp isn't there at all... bare pipe, no wire. Either way, if you're mid-purchase and that line has put a knot in your stomach, let me talk you down. In the huge majority of cases it's a small job, not a reason to walk.

What "main bonding" actually is

Main protective bonding is that thick green-and-yellow conductor running from your fuse box to your incoming metal water and gas pipes, clamped on near where they come into the house. Its job is simple: tie all the big lumps of metal in your home to the same electrical potential, so a fault can't leave a tap or a radiator sitting at a different voltage to everything around it. Get it right and there's no difference in potential to push a current through anyone.

It's worth clearing up one thing straight away, because it trips up loads of people. Bonding is not the same as earthing. Earthing is the path a fault takes back to the supply so the fuse or breaker cuts the power. Bonding is about keeping metalwork at a safe, equal potential in the meantime. They work together, but they're two different jobs... which is exactly why I look at both when I assess a house, not just the bit the survey mentioned.

Why the surveyor flagged it and then got out of the way

A homebuyer's or RICS survey is a generalist's once-over. The surveyor is trained to spot roofs, damp, dodgy timbers and the like... and to notice when something electrical looks off. They'll clock a missing bonding clamp because it's visible. What they won't do is test it, price it, or tell you how serious it is, because that isn't their trade. So they write the line and add "consult a qualified electrician."

That's not them being cagey. It's them staying in their lane, which is the right call. The catch is it leaves you holding a scary-sounding sentence with no context... and the top Google answers on it tend to be written by insurers and gas-certificate firms, not by anyone who's actually crawled into the cupboard and fitted the clamp.

Why it's so common round here

Round Windsor, Old Windsor and Maidenhead I see this constantly, and it's almost always for an innocent reason. A lot of that housing is Victorian or period stock that's been plumbed and re-plumbed for a century. Somewhere along the way (a boiler swap, a bathroom refit, a leak on the incoming main) a length of metal pipe got replaced with plastic. The plumber did nothing wrong; earthing isn't their job and often isn't even visible to them. But the moment plastic goes in, the metal pipework on your side can stop being connected to real earth, and the old bonding is left clamped to a stub that goes nowhere.

The other one I find is bonding that's simply old and undersized... a thin 6mm conductor put in decades ago before supplies were uprated, where today's arrangement wants something heftier. Plenty of these houses are also on a TT earthing arrangement, with their own earth rod, which changes how the whole thing needs assessing.

So... is it dangerous?

Honestly, usually not in the "get out of the house" sense. On an EICR, inadequate or missing main bonding is most often coded C2... potentially dangerous: not a live hazard this second, but something that should be put right because under a fault it could matter. It isn't always a C2, though. Depending on the earthing arrangement and what else is going on in the installation, the same finding can come out as a C3... improvement recommended. Anyone who tells you it's automatically one or the other, sight unseen, is guessing. That's the whole reason it needs assessing properly rather than diagnosed off a survey line.

Here's the reassuring part: putting it right is frequently a small, quick job. If the pipework's accessible and reaching real earth, it can be a fresh clamp and a correctly sized conductor (often 10mm for a modern supply, 6mm on some older arrangements) run back to the board. Nothing like a rewire. It's the kind of thing that rarely troubles a house sale once a proper electrician has looked and said what's what.

And a genuine twist worth knowing: if your incoming water main is plastic all the way, or there's a plastic insert at the point of entry, that pipework may no longer count as something that needs bonding at all... because it's no longer bringing earth potential into the house. So "no bonding" can occasionally be perfectly correct. That's a judgement call for the person with the meter, not a fault to panic over.

Still worried about that line on your survey?

If your survey has flagged missing or inadequate main bonding, the sensible next step is to have the earthing and bonding assessed as a whole... I do that as part of my inspection and testing work, and if the fix ties in at the board I sort that in the same visit (see fuse box replacement). Nine times out of ten I can tell you it's a modest job and set your mind at rest.

I'm Billy, a NAPIT-registered electrician based in Slough, covering Windsor, Maidenhead, Bracknell, Staines and across the Thames Valley. Send me the line from your report or book a free, no-obligation quote and I'll tell you straight what, if anything, it needs. If you want someone local who knows this housing stock, I'm your Windsor electrician.