Short answer: main protective bonding costs £108 to £420 in London in 2026, labour and certification only. One conductor to a gas or water service that sits within reach of the board is £108 — our minimum charge, one hour at the standard rate. Gas and water together in the same cupboard is from £180. A long or awkward run, with the gas meter in an external box at the front of the house and the board at the back, is £240 to £420. If bonding is being done alongside a fuse board change or an EICR on the same visit, it is from £108 on top of that job. Materials — 10 mm² green-and-yellow, BS 951 clamps, labels, conduit or trunking where it is needed — are itemised separately.
That is the cost. The part people actually want to understand is what they are paying for, because “main bonding absent” is one of the most common things to come back on a London EICR and it is almost always written down in a way that tells the owner nothing. This guide explains what bonding is, what it is not, what size the cable has to be, where the clamps go, what code it attracts on a report, and when you genuinely do not need it at all.
We are F & A Electrical — NICEIC registered, Part P registered, working to the current edition of BS 7671, based at Ten 87 Studios on Markfield Road in Tottenham N15. We do this work across Haringey, Hackney, Islington, Enfield, Waltham Forest, Camden, Barnet, Newham and Tower Hamlets. Call 07407 627542 or 07500 721453. 9.32/10 from 242 Checkatrade reviews.
What is main protective bonding, exactly?
Main protective bonding is a green-and-yellow conductor that connects the metal services entering your property — the gas pipe, the water pipe, sometimes oil, sometimes structural steel or a lightning protection system — back to the main earthing terminal at your consumer unit.
It is not there to carry current in normal use. It does one job, and it is worth being precise about it, because the loose explanations are what cause the confusion.
If a fault puts a live conductor in contact with something it should not be touching, the metalwork of your installation rises in voltage for the fraction of a second before the protective device operates. Your gas pipe and your water pipe, being buried in the ground outside, sit at or near the voltage of the earth. For that moment you have two bits of metal in the same house at very different voltages — and a person touching both at once, which in a kitchen or a bathroom is an entirely ordinary thing to be doing, bridges them.
Bonding removes the difference. It ties the incoming services to the same earthing terminal everything else is tied to, so when the voltage rises, it rises together. There is no difference left to drive a current through someone. The proper name for this in BS 7671 is protective equipotential bonding, and “equipotential” is the whole idea: everything at the same potential.
That is also why bonding does not need to be a thick cable to work. It is not carrying a fault current to the ground. It is holding two pieces of metal at the same voltage.
Main bonding, earthing and supplementary bonding are three different things
These three get used interchangeably by estate agents, by surveyors, by builders, and sometimes on a badly written report. They are not the same, they cost different amounts, and they can all be absent at once.
| What it is | Where it is | What it does | What it costs here |
|---|---|---|---|
| Means of earthing / main earthing conductor | From the supply cut-out or an electrode, into the main earthing terminal at the board | Gives fault current a path back to the supply, so the fuse or breaker operates | From £180 — see no main earth |
| Main protective bonding | From the main earthing terminal out to the gas and water services where they enter | Holds incoming metal services at the same voltage as the rest of the installation | £108 to £420 — this page |
| Supplementary bonding | Inside a room, usually a bathroom — pipes, radiator, bath, and the circuit earths | Local version of the same idea, for a room where you are wet and barefoot | From £108 where pipework is accessible |
| Circuit protective conductor (CPC) | In the cable of every circuit, back to the board | Earths the actual sockets, switches and fittings | Missing CPCs usually mean partial or full rewiring |
The one that catches people out is the first two. Bonding is not earthing. Having the first does not give you the second. We have been to houses with beautiful 10 mm² bonding to both services and no means of earthing at all — the earth clamp was on a water main the water company replaced in blue plastic years ago, so the whole installation was sitting there unearthed with a tidy green-and-yellow cable going nowhere useful. That is a C1, danger present, and it is covered properly on our no main earth guide.
Equally, main bonding being present does not mean the bathroom is compliant, and supplementary bonding in the bathroom does not substitute for main bonding. They are separate observations on a report and they are separate line items on a quote.
How much does main bonding cost in London in 2026?
These are our prices. Everything below is labour and certification only, inclusive of VAT, with materials itemised separately on the quote. Nothing is priced below our minimum charge of £108 inc VAT, which is one hour at the standard rate of £90 per hour plus VAT.
| Work | Price from | Notes |
|---|---|---|
| Attend, test and report on the existing earthing and bonding arrangement | £108 | Comes off the job if you go ahead the same visit |
| One main bonding conductor — gas or water — service within reach of the board | £108 | Minimum charge; includes clamp, label and a Minor Works Certificate |
| Both services bonded, gas and water in the same cupboard or within a metre or two | £180 | The commonest job on this list |
| Long or awkward bonding run — external meter box at the front, board at the back | £240 – £420 | Priced on the route, not the property size |
| Replace a corroded, painted-over or non-BS 951 clamp and re-terminate | £108 | Often all a C2 on an older report actually needs |
| Upgrade undersized bonding — 6 mm² out, 10 mm² in | £108 – £240 | Depends entirely on whether the old route can be reused |
| Supplementary bonding in a bathroom, pipework accessible | £108 | Behind a bath panel or in an airing cupboard |
| Supplementary bonding where floors or tiling have to come up | Quoted on survey | We will usually argue for the alternative below instead |
| Earthing and bonding alongside other work on the same visit | £108 | Added to a board change, EICR remedial or rewire |
| New 16 mm² main earthing conductor, cut-out to board, same cupboard | £180 | Different job — see the earthing guide |
| Full TT conversion: electrode, 100 mA S-type main switch, all-RCBO board, bonding | £850 | Only where the network cannot give you an earth |
For comparison, if the bonding has come up on a report alongside an aged board, the sensible move is usually to do both at once. A fuse board replacement is from £550 for a six-way flat board, £650 for a ten-way in a three-bed, £750 and up for twelve ways or more, and bonding alongside it is from £108 rather than a second visit’s minimum charge. Board and EICR together on the same visit is from £690.
Two honest things about the pricing. First, bonding is one of the few jobs in this trade where the cost is almost entirely about the route the cable takes and almost nothing to do with the house. A six-bedroom place in Highgate where the gas and water come into the same understairs cupboard as the board is a £180 job. A one-bed flat where the gas meter is in a communal cupboard two floors down is not.
Second, be careful with anyone who quotes bonding over the phone without asking where your meters are. They are either guessing or they are going to find a reason to change the price on the day.
What size does main bonding have to be?
This is Regulation 544.1.1 of BS 7671, and it is the single most common reason a report says “inadequate” rather than “absent”.
On a PME supply — which is what the great majority of London houses and flats have, where the supply cable’s combined neutral and earth gives you your earth at the cut-out — the minimum size is taken from Table 54.8 and depends on the size of the supply neutral:
| Supply neutral (copper equivalent) | Minimum main bonding conductor |
|---|---|
| Up to and including 35 mm² | 10 mm² |
| Over 35 up to 50 mm² | 16 mm² |
| Over 50 up to 95 mm² | 25 mm² |
| Over 95 up to 150 mm² | 35 mm² |
| Over 150 mm² | 50 mm² |
In practice, for a normal single-phase domestic supply in North London, 10 mm² is the answer, and if you find 6 mm² on the gas, it was almost certainly compliant when it went in decades ago and is not now.
Where the supply is not PME — a TN-S supply with a separate earth in the old lead-sheathed cable, or a TT installation on its own electrode — the rule is different: the bonding must be at least half the cross-sectional area of the main earthing conductor, with a floor of 6 mm² and no requirement to go above 25 mm² in copper.
Supplementary bonding, under 544.2, is much smaller because it only runs between items in one room: 2.5 mm² where it is sheathed or otherwise mechanically protected, 4 mm² where it is run bare and unprotected. Where it connects an exposed-conductive-part to an extraneous-conductive-part it must have a conductance not less than half that of the circuit protective conductor, and still not less than 4 mm² if it is unprotected.
A note on the 6 mm² you will often find on the water in a 1970s or 1980s house. It is undersized by today’s table, but it is doing real work, and whether it needs replacing depends on whether the route can be reused. If the old 6 mm² runs cleanly from the board to a clamp you can reach, pulling a 10 mm² through the same path is an hour. If it is buried in a wall behind a fitted kitchen, it is a different conversation and surface trunking along a skirting is often the sane answer.
Where do the clamps go, and why does the position matter?
The connection has to be made within 600 mm of the meter outlet union — on the consumer’s side of the gas meter, and on the house side of the water stopcock — or, where the meter is outside, at the point where the service enters the building.
The reasoning is practical rather than bureaucratic. Anything upstream of that point belongs to the gas or water undertaker and can be cut, replaced, or swapped for plastic without anybody telling you. Anything more than 600 mm downstream risks a length of pipe between the clamp and the entry point that can be removed during a plumbing job, leaving the bond connected to a dead end.
The clamp itself has to comply with BS 951, and it has to carry the label reading “Safety Electrical Connection — Do Not Remove”, which is Regulation 514.13.1. That label is not decoration. It is the only thing standing between your bonding and a plumber who needs the pipe clear for ten minutes.
Four things we look at on every bonding inspection, which is also a reasonable list for you to check yourself with a torch:
- Is the clamp on the right pipe? We find bonds clamped to a radiator tail, a hot water pipe in an airing cupboard, or a copper tail downstream of a plastic push-fit joint. None of those bonds the incoming service.
- Is it on the right side of the meter? A bond on the supplier’s side of a gas meter is not compliant and the meter can be removed, taking the bond out of circuit.
- Is the pipe actually metal all the way out of the building? This is the big one in London, and it has its own section below.
- Is the connection sound? Painted over, corroded in a damp brick meter cupboard, loose on a pipe that has been lagged over, or a clamp with the label long gone — all common on the ex-council and converted stock round Tottenham, Wood Green and Walthamstow.
Why does my EICR say main bonding is absent, and how serious is it?
In the guidance most London inspectors work to — Electrical Safety First’s Best Practice Guide 4, which is what the codes on a domestic report are drawn from — absence of main protective bonding to extraneous-conductive-parts entering the premises is a C2: potentially dangerous. That is not a C1 and the distinction matters. A C1 means danger is present right now. A C2 means the installation is safe until something else fails, and then it is not.
A C2 makes an EICR unsatisfactory, which for a landlord means remedial work inside 28 days or sooner if the report specifies, under the Electrical Safety Standards in the Private Rented Sector regulations. For an owner-occupier nobody is going to make you fix it, but it will come up on a sale, and it is a cheap thing to have hanging over a transaction.
Undersized bonding is the one where you will see honest inspectors disagree. The guidance treats an inadequate cross-sectional area as a C2 where the conductor is below 6 mm² or where there is evidence of thermal damage. A sound 6 mm² bond on a modern PME supply, where the table now wants 10 mm², is routinely coded C3 — improvement recommended, report still satisfactory — and that is a defensible call. What should not happen is a blanket C2 on every 6 mm² in the borough to generate remedial work, and it should never be ignored entirely either.
The other code you will meet is FI, further investigation required. If the inspector could not get to the gas meter because it is in a locked communal cupboard, or the water entry could not be found, a conscientious report says FI rather than guessing. That is not the inspector being awkward. Our guides on what C1, C2 and C3 mean, the fifteen most common C2 faults and what a limitation means go through all of this in more detail, and EICR unsatisfactory — what happens next covers the 28 days.
When you genuinely do not need main bonding at all
Here is the part that gets left out of most of what is written about this, and it saves people money.
The requirement is to bond extraneous-conductive-parts — metal that is liable to introduce earth potential into the building from outside. If the thing is not liable to do that, there is nothing to bond, and a bonding conductor to it achieves precisely nothing.
So in a modern flat where the water comes in through plastic pipe and there is no gas at all — which describes a great deal of what has been built at Tottenham Hale, along the High Road, at Millbrook Park and across the Brent Cross Town development — there may be no extraneous-conductive-parts to bond. Absence of main bonding in that flat is not a defect. It is correct. A report that codes it C2 anyway has not looked at the pipework, and we have seen that mistake more than once on reports owners bring us for a second opinion.
The same logic applies to plastic internal plumbing with copper tails. A copper tail fed by a plastic rising main is not introducing earth potential from anywhere. Bonding it is harmless and pointless.
Two caveats, both important. First, this is a judgement that has to be made and recorded — the inspector should note on the report that the services are non-metallic, rather than leaving a blank box that reads as an omission to the next person. Second, if there is any metallic service at all, it gets bonded, and if a plastic rising main changes to copper before it enters the building, the copper length is a metallic service entering the building.
Do I still need supplementary bonding in the bathroom?
Usually not — and this is the other place where money gets spent needlessly.
Regulation 701.415.2 allows supplementary bonding to be omitted in a location containing a bath or shower, but only where all three of the following are true at the same time:
- Every final circuit of the location complies with the requirements for automatic disconnection in Regulation 411.3.2 — which means the earth fault loop impedance has been measured and is inside the maximum for the protective device.
- Every final circuit of the location has additional protection by a 30 mA RCD, in accordance with 415.1.1.
- All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding — in other words, the main bonding is properly in place.
Read condition three again, because it is the one that decides the money. The omission route is only open to you if the main bonding is there. In a 1930s terrace off Lordship Lane with metal water and gas, a rewirable fuse board with no RCD and no bonding at the intake, supplementary bonding in the bathroom is required and is doing genuine work. In the same house after a board change to RCBOs and a proper 10 mm² bond to both services, it can come out — or rather, it no longer needs to go in.
That is why we will nearly always rather spend £180 on main bonding and the board than take up a tiled bathroom floor to chase supplementary bonding. Same compliance, better installation, less mess. Our bathroom electrics guide covers the zones and the rest of Section 701, and electric shower installation deals with the loads.
One thing to be clear about: taking existing supplementary bonding out is not something to do casually. If it is there and it is sound, it is not hurting anybody. The regulation permits omission on a new or altered installation that meets the conditions — it does not instruct you to rip out what is already fitted.
What if my water main is plastic?
Then your water pipe is not an extraneous-conductive-part, there is nothing to bond, and — far more importantly — it is not an acceptable means of earthing either, and it never was meant to be relied on.
This is the defect we find more than any other in North London. Thames Water has replaced a great deal of lead and iron service pipe with blue MDPE across Haringey, Hackney, Enfield and Waltham Forest. They do the work at the boundary. They do not inspect your consumer unit, and they have no reason to. What they leave behind is an earth clamp sitting on a short length of copper inside the house that is no longer connected to anything in the ground.
From the cupboard it looks perfect. Clamp present, label present, green-and-yellow going up to the board. Tested, it is a C1. The full version of that story, including what UK Power Networks will and will not do about it, is on no main earth — what does it mean on an EICR. The short version: metallic water utility pipe is no longer acceptable as a means of earthing precisely because the water company can replace any length of it in plastic without telling anyone.
And note the asymmetry. A plastic water main removes the need to bond the water. It does not remove the need to bond the gas, if the gas is still metal — which it usually is.
Does bonding work have to be notified to Building Control?
Main bonding on its own is not normally notifiable work under Part P in England. It is not a new circuit, it is not a consumer unit replacement, and it is not an addition or alteration to a circuit in a special location. What you should get for it is a Minor Electrical Installation Works Certificate, with the conductor sizes, the clamp positions and the test results on it — that is your evidence it was done and done properly.
Where bonding is done as part of a board change, the board change is notifiable, it goes on a full Electrical Installation Certificate, and we notify it through our NICEIC registration rather than you dealing with the council. Our what is Part P certification guide explains how that works, and BS 7671 Amendment 4 (2026) covers what changed in the current edition.
Keep the certificate. It is the piece of paper that stops you paying for the same work twice when the next report comes round, and it is the one a buyer’s solicitor will ask for.
What we actually find in North London homes
Not invented jobs — the patterns that come up again and again across the patch we work.
Victorian and Edwardian terraces, Tottenham and Wood Green. Gas bonded in 6 mm² from a 1980s board change, water bonded to a pipe the water company has since renewed in plastic. One undersized, one pointless, and the actual means of earthing often resting on the same dead pipe. These are the houses where the honest answer is to look at the intake first and the board second.
External meter boxes on the A406, Watford Way and Great Cambridge Road frontages. When the gas meter went outside, the bond frequently did not follow it. We find a clamp still inside on a capped stub, or no bond at all and a split meter-box door with corroded tails behind it. This is the £240 to £420 job on the table above: the route from a front meter box back to a board under the stairs at the rear is rarely short.
Big houses cut into flats off Lordship Lane, St Ann’s Road, Mare Street, Graham Road and the Hornsey and Harringay grid. One intake, one set of services, and bonding that was done for the original house and never revisited when it became three flats with twin-and-earth sub-mains up the common stair. Each flat’s board needs to see a main earthing terminal, and the services need bonding once, properly, at the intake — not three half-hearted attempts in three hallways.
Ex-council right-to-buy leasehold around Northumberland Park, White Hart Lane, Broadwater Farm and the Hackney and Waltham Forest estates. The meter and board are in a communal cupboard behind a door you do not control, and the gas riser is in another one. Access and isolation go through the freeholder or managing agent, the brick cupboards are damp, and corroded clamps and tails are routine. We quote these knowing the first visit may be about getting into the cupboard.
Kitchen refits. The single most common way a good bond is lost. The sink unit comes out, the clamp is in the way, somebody takes it off to get the pipe clear and nobody puts it back. If you have had a kitchen done in the last few years and nobody issued you a certificate, this is worth a torch and five minutes. Our kitchen electrical requirements guide covers the rest of what gets missed.
New-build and converted flats with no gas. Heat networks and all-electric flats at Tottenham Hale, along the High Road, at Millbrook Park and Brent Cross Town. Nothing to bond, and the certificate should say so in words rather than leaving an empty box. These flats also tend to have no spare ways in the board, which is a capacity question rather than a condition one.
Landlords and HMOs. Bonding is one of the three things we check before anything else on an HMO EICR, because a C2 on bonding is cheap to clear and will otherwise sit on an unsatisfactory report for a fortnight while a licence renewal waits. Licensing itself varies street by street — check your council’s current scheme for your address.
Frequently asked questions
Can I fit main bonding myself?
Physically, it is a cable and two clamps. In practice, no — not because of the cable, but because the work is only worth anything if somebody measures what they have connected. The point of bonding is continuity between the service and the main earthing terminal, and you cannot see continuity. We test it, record the reading and issue a Minor Works Certificate. A bond nobody has tested is a green-and-yellow cable with no evidence behind it, and it will come straight back as a C2 or an FI on the next report.
My surveyor said I need “earth bonding”. Is that main bonding or earthing?
“Earth bonding” is not a term in BS 7671, and when a surveyor uses it they usually mean they could not see a green-and-yellow cable on the pipes. It could mean either of the two jobs in the table above, or both. Ask for a photograph of the consumer unit and the meter positions, or have an electrician look — it is the difference between £108 and a C1 that needs UK Power Networks involved.
Does a new fuse board include the bonding?
It should always include checking it, and any decent quote for a fuse board replacement prices the bonding as a visible line rather than burying it. We charge from £108 for bonding alongside a board change. Be wary of a cheap board quote that does not mention earthing or bonding anywhere — a new consumer unit on an installation with no bonding and no earth is a new consumer unit with the same defects behind it, and the certificate will have to say so.
The gas engineer says the bonding is the electrician’s job and my electrician says ask the gas engineer. Who is right?
The electrician. Main protective bonding is part of the electrical installation and sits under BS 7671, so it is ours to install, test and certify. A Gas Safe engineer is right to refuse to work on a meter with no bond present and right to tell you about it — that is them doing their job — but the clamp and the conductor are electrical work. The same split applies at the supply end: who owns the cut-out, the fuse and the tails is set out in who is responsible for the main fuse, cut-out and meter tails.
My bonding goes to the gas but not the water. Is that a fail?
It depends entirely on whether the water is metal where it enters the building. If it is copper or iron coming out of the ground, it needs bonding and its absence is a C2. If it is plastic to the boundary, there is nothing to bond and the report should say that in words. Ten minutes with a torch at the stopcock answers it, which is why we would rather come and look than quote you blind over the phone.
How long does the work take?
A straightforward bond to one service in the same cupboard as the board is under an hour. Gas and water together, in reach, is an hour to ninety minutes. A run from an external front meter box to a board at the back of the house is a half day, mostly spent on the route and making it look like it belongs there rather than on the electrical connection. Power is off for minutes, not hours.
Will bonding fix my RCD tripping?
No, and if anyone tells you it will, get a second opinion. Bonding and nuisance tripping are unrelated problems — tripping is usually accumulated earth leakage across several circuits, a wet external circuit or a failing appliance, and it is a fault-finding job. Correct bonding is a safety requirement regardless of whether anything is tripping.
Book it, or just get a straight answer first
If bonding has come back on a report, send us the report. We will tell you which of the three jobs above it actually is, what it costs, and whether it is worth doing on its own or waiting until the board goes. That conversation is free; if we attend to test the earthing arrangement it is £108, and it comes off the job if you go ahead the same visit.
F & A Electrical, Ten 87 Studios, Markfield Road, London N15 4QA. NICEIC registered, Part P registered, City & Guilds Level 3, £5m public liability, working to the current edition of BS 7671. 9.32/10 from 242 Checkatrade reviews.
Call 07407 627542 or 07500 721453. We cover Haringey, Hackney, Islington, Enfield, Waltham Forest, Camden, Barnet, Newham and Tower Hamlets from Tottenham N15 — the full list is on our London service areas hub, with pages for Tottenham, N17, Hackney and Walthamstow among others.
More in this series: no main earth on an EICR · what an EICR actually checks · EICR cost London 2026 · fuse board replacement · PAT testing · and the full electrical guides index.