Earthing and Bonding Explained: What That Line on Your EICR Actually Means

You’ve had an electrical report done, you’re reading through it with a brew, and there it is. “Main protective bonding absent to gas.” Or “inadequate bonding.” And a C2 next to it.

Most people have no idea what that means. Fair enough.

I’ve been an electrician for over 25 years, and bonding is one of the things I explain most after an inspection. So here it is, in plain English.

Quick answer

Earthing gives electricity a safe path to take if something goes wrong, so the fuse, breaker or RCD can switch the circuit off quickly. Main bonding is a green and yellow cable that connects your incoming metal gas and water pipes to the main earth, so they can’t sit at a dangerous voltage during a fault. Missing or inadequate main bonding is a common observation on EICRs, and in most homes it’s a fairly quick job to put right.

What is earthing and why does it matter?

Think about an old metal cased appliance. If a live wire inside it came loose and touched the casing, that casing could become live. Touch it, and the electricity looks for a way to earth through you.

Earthing stops that. Metal parts that could become live are connected back to earth through the circuit’s protective conductor (the earth wire).

In a fault, a large current flows down that earth path, and that sudden rush makes the protective device trip. The whole point is to let the fault clear quickly, ideally before anyone gets hurt.

Electrical Safety First has a good simple explanation if you’d like a second opinion on the basics.

Earthing arrangements in plain English

Your earth has to come from somewhere. In most UK homes, it’s one of three types. Electricians write these as TN S, TN C S and TT on the report.

TN S (earth from the supply cable sheath)

Common in older terraces and semis, including plenty of the older streets around Rotherham and Sheffield. The earth is provided by the metal sheath of the electricity company’s cable.

How to spot it in general terms: you’ll often see an earth wire clamped onto the lead or metal sheath of the big incoming cable, near where it enters the cutout (the sealed fuse unit before your meter).

TN C S, often called PME

This is the most common arrangement in newer homes and in many older ones where the supply has been updated. The supply company combines neutral and earth in their cable, and gives you an earth terminal at the cutout.

How to spot it in general terms: there’s usually a small label near the meter saying something about “Protective Multiple Earthing”, and the earth cable connects to a terminal block on or beside the cutout.

PME is safe when installed properly, but it relies heavily on good main bonding.

TT (your own earth rod)

Here the house has its own earth, usually a metal rod driven into the ground outside. You tend to see TT on rural properties and some houses in villages on the edges of Maltby and Doncaster, where the supply cable doesn’t provide an earth.

How to spot it in general terms: an earth cable leaves the house and goes to a rod, sometimes under a small inspection cover in the ground.

A quick safety note

Look, don’t touch. The cutout belongs to the network operator and is live. If anything looks damaged or loose, give an electrician a ring.

Main protective bonding to gas and water

Main protective bonding is a green and yellow cable that runs from your main earthing terminal (usually near the consumer unit or meter) to the metal gas pipe and metal water pipe where they come into the property.

Why does it matter?

Metal pipes run all over the house and out into the ground. During a fault, a pipe and something electrical nearby could sit at different voltages.

Bonding ties them together, so if something does go wrong, the metalwork you might be touching is held at a similar voltage. That massively reduces the risk of a shock.

Where should it be?

• Gas: on the metal gas pipe, close to the meter, on the house side, and before the pipe branches off
• Water: on the incoming metal water pipe, close to where it enters the building, usually near the stopcock and after it on the house side

What does it look like?

You should see:

• A green and yellow cable, noticeably thicker than the cables in your sockets. In a lot of modern homes on a PME supply, it’s commonly 10mm² copper, although the right size depends on the installation
• A metal earth clamp around the pipe
• A small label on the clamp saying “Safety Electrical Connection, Do Not Remove”

What about plastic water pipes?

Lots of homes in Wickersley, Bramley and across South Yorkshire have had their old lead or copper water main replaced with blue plastic pipe.

If the incoming pipe is plastic, the water supply might not need main bonding at that point, because plastic doesn’t bring earth into the house. But it isn’t automatic.

Sometimes the plastic changes to copper just inside the house, and that copper can still need looking at. An inspector will check what’s there and may test it before deciding. If someone says “it’s plastic, it’s fine”, get that properly confirmed.

Supplementary bonding in bathrooms

Many older bathrooms have extra green and yellow cables linking the pipes, radiators and metal bath. That’s supplementary bonding.

Under the current wiring regulations (BS 7671), it can often be left out in a bathroom, but only when certain conditions are met. In simple terms, all the circuits in the bathroom need RCD protection, they need to meet the requirements for disconnecting quickly in a fault, and the metal pipework needs to be properly connected back to the main bonding.

That’s why many newer bathrooms have none, and that can be fine.

What it doesn’t mean is that you can rip out existing bathroom bonding because you’ve got an RCD. If the conditions aren’t met, supplementary bonding can still be needed. That’s a call for your electrician to make after checking.

What “inadequate bonding” on a report usually means

When I see a report mention bonding, it’s usually one of these:

• No main bonding at all to the gas, water or both
• Undersized cable, such as an old thin earth cable from decades ago
• Bonding in the wrong place, for example on a pipe after it’s branched off
• Loose, painted over or corroded clamps
• Missing labels
• Bonding that’s been cut or disconnected during other work

How is missing bonding coded on an EICR?

Missing main bonding is commonly coded C2 (potentially dangerous) on an EICR. That’s in line with the industry guidance inspectors use.

However, the code is the inspector’s decision, based on what they actually find and test in your home. Undersized or hidden bonding, for example, can be coded differently depending on the situation. So I wouldn’t guess what your own report might say without seeing the property.

If you’re a landlord, it’s worth knowing that landlords in England must get C1 and C2 items put right within the timescale set out in the private rented sector electrical safety rules. There’s more on this on GOV.UK.

Owner occupiers don’t have a duty to have their electrics tested, but a C2 is still worth sorting for your own family’s safety. We can also carry out an EICR in Rotherham if you’d like a full picture of your installation.

Is it a big job to fix?

Usually not. In most homes I work in, adding or replacing main bonding is a fairly quick and tidy job. It often takes a few hours rather than days.

It depends on how far the pipes are from the main earth and how easy the cable route is. Sometimes it’s a straight run under the stairs, sometimes it means lifting a floorboard or two.

I won’t put a price on it here, because every job is quoted properly after we’ve had a look. It’s free to ask.

Please don’t disconnect bonding clamps

That label says “Do Not Remove” for a reason. Bonding cables should stay connected.

If you’re boxing in pipes or fitting a new kitchen, keep the clamp visible and accessible. Hidden bonding can be flagged on your next inspection.

When plumbers cut through bonding

This crops up a lot. A new boiler or kitchen refit, and the pipe with the bonding on gets swapped out. The clamp ends up dangling, or in a drawer.

Good plumbers and gas engineers are aware of this, and many use a temporary bonding lead while they work. But if you notice a loose green and yellow cable after any pipework job, don’t ignore it. Get it reconnected by someone competent.

Frequently asked questions

What is the difference between earthing and bonding?

Earthing connects metal parts of your electrical installation to earth so faults can clear quickly. Bonding connects other metalwork, like gas and water pipes, to that earth so everything stays at a similar voltage during a fault.

Where is the main bonding in my house?

Look for a green and yellow cable with a metal clamp on your gas pipe near the meter, and on your incoming water pipe near the stopcock.

Does a plastic water pipe need bonding?

Not always. A plastic incoming supply often doesn’t need bonding at that point, but any metal pipework further in may still need checking by an electrician.

Do I need supplementary bonding in my bathroom?

It depends. It can often be left out where the bathroom circuits have RCD protection and meet the other conditions in BS 7671. An electrician needs to check this on site.

Can I fit bonding myself?

I’d advise against it. It needs the right cable size, position and testing afterwards, so it’s a job for a qualified local electrician.

Related services and guides

• EICR testing in Rotherham
• Failed EICR: what to do next
• Consumer unit and fuseboard upgrades
• RCD, RCBO, AFDD and surge protection explained
• Power to your garage, shed or outbuilding

Contact MP Electrical

If you need help with earthing and bonding or any electrical work in Rotherham or South Yorkshire, MP Electrical are happy to help.

📞 Call our office on 01709 645115

🌐 Visit: rotherhamelectrician.co.uk

📅 Book online: Book your appointment online

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Related reading: RCD, RCBO, AFDD and surge protection explained, consumer unit upgrades and our recent work.