If you are installing a new consumer unit, or completing electrical inspections, you’ll need to be familiar with the meter tail regulations in force at the current time.
Whilst there is no separate “meter tail regulations”, sections of BS7671 (18th edition wiring regulations) does deal with installation of cables, of which the meter tails must also comply.
Meter Tail Regulations
The parts of BS7671 which apply to meter tails can be broadly summarised in the following sections.
As this guide is intended to assist with 18th edition electrical inspections, we will focus mainly on what you should be checking during an EICR.
However the sections below give some indication of what you need to be doing when installing meter tails on a new installation.
Requirement for adequate support for Meter Tails/Cables
This is something which is far and away the most common issue with meter tails.
They are often hung from the meter over to the consumer unit (or even fuse board on older installations). This is often on the fashion of a large “lazy loop” as the thick cable does not bend too easily.
I have personally come across an instance where a tenant has hung an umbrella by the handle from the drooping meter tails!!
Loose connections within main switches and electric meters are a huge source of fire risk.
The very first and obvious thing about meter tails should be that they are secured in a way that does not place strain on the terminations.
This could take the form of a meter tail gland on the consumer unit, although these are a fairly modern addition to installations.
Another acceptable method would be using clips of some kind. Obviously on an 18th edition “installation” you would need to use heat resistant fixings.
However when inspecting older installations then pay particular attention to the cable to ensure it is secured adequately.
The meter tails often pass from an external cabinet through a wall cavity to the consumer unit.
In most instances like this the cable passing through the wall is providing adequate support, assuming the length of tails within the meter cabinet are not too long.
Do Buried Meter Tails Need RCD protection?
It may sound odd, but the answer is yes, meter tails buried in walls, less than 50mm from the surface will require additional protection by 30mA RCD.
A common installation method with meter tails is to run then between an external meter cabinet, through the cavity, into the consumer unit through the rear of the board.
Following the meter tail regulations to the tee would frown on this installation method as the cables being within the cavity is not a recognised installation method as per BS7671.
I’m not suggesting you start recording that on EICRs as the simple fact is, it presents no apparent risk to the cable.
Cables buried less than 50mm underneath the wall surface is a different matter though. To be honest it’s not something which we see very often, BUT I can think of a very specific installation type which often has buried T&E as the meter tails/submain to the consumer unit.
This would be older buildings which have been converted to flats. I can think of a couple of instances I have seen this in old pubs which have been converted.
The usual setup there is a switch fuse between the meter and a piece of 16mm T&E used as the submain cable. Quite often this is run throughout the building to each individual flat.
Whilst it is impossible to follow the route of the cable through the fabric of the building, it’s hard to see how they could run it without at least part of the cable being buried inside the wall.
Because of the more serious nature of the submain cable, if you come across this then I would advise to strongly consider upgrading it.
The ideal scenario here would be to use SWA cable as it does not require RCD protection.
Adding a 30mA RCD upfront could cause alsorts of nuisance tripping issues, and does not really meet the requirement for division of circuits to minimise inconvenience.
Meter Tail Regulations – Identification Of Conductors
When considering meter tail regulations, it should be remembered that the conductors need to be correctly identified.
On a single phase supply you will simply have L & N, however on 3 phase supplies all 3 phases will require separate identification, together with the Neutral conductor.
This would generally be achieved by colour of conductor, however externally to the meter there should be no unsheathed basic insulation.
Some meter tails are now coming with coloured sheathing in order to accurately identify the conductors.
However plain grey sheathed meter tails are most common. These are indistinguishable from each other without external identification, in the way of letters, numbers or colouring
This can achieved in a number of ways:
- Using coloured bands, tape or cable ties. These could be in either set of BS7671 colours (if completing EICRs). However if you were completing a new installation then they would need to be the new harmonised colours.
- Lettering. This can be as simple as writing on the outer sheathing with a marker pen. Obviously this would need to be large enough to read and at more than one single point along the length of the tails.