Meter Tails: The Heavy Cables Between Your Meter and Consumer Unit

The electrician finishes the new consumer unit on the day it's needed, then stops dead. The meter moved to a new external box during the extension, three metres further away, and the old tails won't reach. He can't join in a longer length, and he can't touch the meter end because it's sealed by the supplier. The job now waits two weeks for the meter operator to reconnect. A dull length of cable nobody thinks about has stalled the whole electrical first fix, because everyone assumed someone else owned it.

What they are and what they're for

Meter tails are the short, heavy single-core cables that connect your electricity meter to the main switch of your consumer unit (the fuse box where the supply splits into circuits). They're called "tails" because they're the stub of cable that hangs off the meter and the consumer unit, bridging the gap between the two. On almost every UK home that gap is less than a couple of metres, which is why the cables are short and why most people never see or think about them.

There are normally three of them on a standard single-phase domestic supply: a live tail and a neutral tail, plus the main earthing conductor that bonds the installation to earth. The live and neutral carry the full incoming current of the property, so they're thick: typically 25mm cross-sectional area on a modern supply. That 25mm refers to the area of the copper inside, not the diameter of the cable. The earth is usually a size smaller, commonly 16mm, because it only ever carries fault current, not the normal running load.

They matter during an extension for one reason: the moment your meter moves, your consumer unit moves, or your supply is upgraded, the tails have to be renewed or extended to suit. And the work is split between two different people who are not allowed to do each other's half. Get that split wrong and the build stops.

The standard domestic sizing

The size of the tails follows the size of the supply fuse, the cut-out fuse the network operator fits ahead of your meter. Most modern UK homes have a 60A, 80A, or 100A single-phase supply, and 25mm tails are the standard match across that range. Older properties, smaller flats, or homes on a 60A supply may have 16mm tails, which were the norm for decades and are still perfectly legal where the supply and main switch are rated to suit.

The colours follow the modern harmonised code. The live tail is brown, the neutral tail is blue, and the earth (the main earthing conductor) is green-and-yellow. Older installations may have red and black tails, which mean exactly the same thing (red was live, black was neutral) but predate the colour change. If your electrician is renewing the tails as part of the work, they'll come out in brown and blue, and any short length of bare or wrong-coloured conductor at a termination gets sleeved in the correct colour so the connection is unambiguous.

Meter tails are double-insulated, sometimes called double-sheathed. The conductor has its coloured PVC insulation, and over that sits a second layer of insulation. This second layer matters because the tails run exposed between the meter and the consumer unit, often in a cupboard or under stairs where they can be knocked or rubbed. The double layer means a single nick doesn't expose live copper. Cable type 6181Y is the common single-insulated version; the genuinely double-insulated grade is what belongs on this run.

The one number that has to line up is the rating of the tails against the rating of the main switch in your consumer unit and the supply fuse ahead of the meter. A 100A main switch fed by 16mm tails is a mismatch: the cable can't safely carry what the switch and fuse would allow through it. The tails, the main switch, and the cut-out fuse all need to agree.

The length limit between meter and consumer unit

Here's the constraint that catches people out when a meter moves. The run of tails between the meter and the consumer unit is meant to be kept short. The long-standing guidance, and what most distribution network operators (DNOs) and meter operators expect, is a maximum of around three metres of tails between the meter and the main switch, with shorter being better.

The reason is protection. The tails between the meter and the consumer unit sit on the supply side of your main switch, and on that stretch the only thing protecting the cable against a fault is the network operator's cut-out fuse, which is a large fuse sized to protect their equipment, not your tails. A short run limits the length of cable that's relying on that distant fuse. A long, unprotected run of tails is a fire risk the regulations and the network operators want to avoid.

This isn't a single hard rule written into one regulation with a precise figure, which is why you'll see slightly different numbers quoted. It's a combination of network operator policy, meter operator requirements, and good practice that converges on "keep it short, and don't exceed about three metres without doing something about it." If your meter and consumer unit genuinely need to be further apart, for example because the meter has gone to a new external box at the front of the house and the consumer unit is staying inside, the answer is not simply a longer run of tails. You add an isolator or a switch-fuse near the meter so the long run downstream of it is properly protected, or you rearrange the layout so the consumer unit sits closer to where the meter ends up.

The supplier's seal: the line you cannot cross

This is the part homeowners most often get wrong, and it has legal teeth. The connection at the meter end of the tails belongs to the meter operator and the network operator, not to you and not to your electrician. That connection is sealed, with a small plastic or wire seal on the meter and the cut-out, and breaking that seal without authorisation is an offence under the Electricity Act. The seal is there to prove nobody has interfered with the metering or tapped the supply ahead of the meter.

What that means in practice is a hard division of labour. Your registered electrician does the consumer unit end: they terminate the tails into your new main switch, set up the consumer unit, and test the installation. They do not break the meter operator's seal to reconnect the tails at the meter. That reconnection, and the resealing afterwards, is done by the meter operator or the DNO.

So when a meter moves during an extension, the sequence is: the network operator or meter operator disconnects and moves the meter (and often fits new tails at their end to suit the new position), your electrician sets up and connects the consumer unit end, and the supplier's representative makes and seals the final meter-end connection. Three parties, in order. If you assume your general builder or even your own electrician can "just move the meter," the build hits a wall, because none of them are allowed to.

Henley blocks and isolators: working without the supplier on site

There's a piece of kit that solves the "everything waits on the supplier" problem, and a homeowner who knows to ask for it saves themselves real grief. The issue is that once the tails are sealed at the meter, your electrician can't isolate the consumer unit from the supply without the supplier pulling the cut-out fuse, which means another visit and another seal. Fit the right component at install time and you sidestep that entirely.

A Henley block (a service connector block) is a moulded junction block that lets the single pair of tails from the meter split out to feed more than one consumer unit, or to provide a tapping point, without making an unauthorised joint. It's the standard way to feed a second consumer unit, for example a sub-board for an extension or a garage, from one meter. The tails go into the block, and two sets of tails come out, all under one insulated cover.

A supplier isolator (also called a DNO isolator or a 100A double-pole isolating switch) is a switch fitted between the meter and the consumer unit. It lets you, or your electrician, switch off the whole supply downstream of the meter without touching the sealed meter connection at all. With an isolator fitted, future consumer unit work, or even swapping the board, can be done without the network operator coming out to pull the fuse. It's a small extra cost at install and it removes the supplier from the critical path of any later work.

Not every network operator will let you fit an isolator on their side of the meter without authorisation, and some prefer to fit their own, so the position varies by region. But raising it with your electrician before the consumer unit goes in is worth it. The alternative, finding out after the fact that any future board change means booking the DNO to disconnect and reseal, is exactly the kind of avoidable delay this product is full of.

Where this comes up in an extension

Meter tails surface at a handful of predictable moments on a build, and they all trace back to something moving.

The classic trigger is the meter relocation. An extension often means the existing meter is in the way, or the homeowner takes the opportunity to move an internal meter to a new external meter box for easier reading. New tails connect the relocated meter to the consumer unit, and the meter-end connection is sealed by the supplier once it's made.

The second trigger is relocating or replacing the consumer unit. If the new board goes in a different spot, or the extension needs more circuits than the old board could carry, the tails have to be renewed to reach the new position and to match the new main switch rating.

The third is a supply upgrade. If the property is moving from a 60A or 80A supply up to 100A to cope with the extra load of an extension (electric hob, oven, underfloor heating, an EV charger later on), the network operator upgrades the cut-out fuse, and the tails are renewed to 25mm to suit if they weren't already.

The comparison table below sets out the typical tail products and current retail prices so you can sanity-check what your electrician quotes for the cable itself. The cable is a small part of the job; the labour and the supplier's meter visit are the bulk of the cost.

Cost: the cable itself

Meter tails are sold by the metre, by the coil, or by the 50m drum, and as colour-matched kits that pair the brown, blue, and green-yellow together for a single supply. For a normal renewal you need only a few metres of each, so a short coil or a kit is usually the sensible buy rather than a full drum. Prices below are current 2026 retail, inclusive of VAT.

The colour-matched kits are the easy option for a single supply renewal: one pack gives you the brown live, blue neutral, and green-yellow earth in matching lengths. The grey single-core option exists because grey is sometimes used as a neutral or as a sleeved live in certain arrangements; for a standard domestic job, brown live and blue neutral is what you want. Buying a full 50m drum only makes sense if you have several runs to do or want a reserve; for one consumer unit it's far more cable than you need.

How they're worked with

Meter tails are stiff. The 25mm conductor is a thick bundle of copper strands and the double insulation adds bulk, so the cable doesn't bend into tight corners easily and needs gentle radii rather than sharp turns. An electrician strips the ends carefully so the full conductor seats into the main switch terminal, then tightens the terminal screw to the right torque. A loose tail termination is a classic cause of overheating, because all the property's current passes through that one connection.

Where a tail terminates, any exposed conductor that isn't already the right colour is sleeved with coloured PVC sleeving to identify it. The run between meter and consumer unit should be supported and clipped so the cables aren't hanging on their terminations, and kept clear of anything that could chafe the outer insulation over time.

You won't be doing any of this yourself. Terminating tails into a live or soon-to-be-live consumer unit, and anything near the meter, is work for a registered electrician and, at the meter end, for the supplier. Knowing what's involved lets you read a quote and spot when a corner is being cut.

Common mistakes

Undersizing the tails. Fitting 16mm tails to a 100A supply with a 100A main switch is a mismatch the cable can't safely carry. The tails have to match the supply fuse and the main switch rating. On a modern 100A supply that means 25mm.

Running an over-length, unprotected run. Stretching tails well beyond about three metres to reach a consumer unit that's ended up far from a relocated meter leaves a long cable on the supply side of the main switch, protected only by the distant cut-out fuse. Keep the run short, or fit an isolator or switch-fuse near the meter.

Breaking the supplier's seal. Cutting or removing the seal on the meter or cut-out to reconnect the tails yourself, or letting a builder do it, is an offence. The meter-end connection and reseal belong to the meter operator or network operator. Only they may do it.

Assuming the electrician can move the meter. A registered electrician sets up the consumer unit end. They cannot make or break the sealed connection at the meter. If you plan the build on the assumption that your electrician will "just move the meter," the work stalls until the supplier attends.

No isolator, so everything waits on the network operator. Without a Henley block or supplier isolator, your electrician can't isolate the consumer unit from the supply without the DNO pulling the cut-out fuse. Every later board change then needs a supplier visit. Fitting an isolator at install removes that dependency.

Mismatched tails and main switch rating. The tails, the main switch in the consumer unit, and the cut-out fuse all have to agree on rating. A 100A switch behind 16mm tails, or 25mm tails terminated into an undersized switch, is the kind of mismatch that surfaces on an inspection report.

Where you'll need this

• Utility meter relocation - new tails connect the relocated meter to the consumer unit, with the meter end disconnected, reconnected, and sealed by the supplier
• First fix electrics - the consumer unit and its supply tails are set up as the electrical first fix begins, around the supplier's meter date

Meter tails come up on any extension, conversion, or renovation where the meter moves, the consumer unit is relocated or replaced, or the supply is upgraded. The cable is cheap and the run is short, but the split of responsibility between your electrician and the supplier, and the seal you cannot touch, are what determine whether the work flows or stalls.