Electric cables in the UK
general internal cable - three plus earth
using the new coloured cable
It should be noted that in England and Wales from 1st January 2005, Building Regulations Part P requires that only certified persons carryout electrical installation work, or that the work is certified upon completion to satisfy the local Building Control Department.
All details regarding electrical wiring and installation on practicaldiy.com are for information purposes only.
Modern Electric Cables:
Cable for domestic 230 volts AC electric power circuits is usually available in the UK to BS 6004 (Electric cables).
New colours for the internal cores (referred to as 'harmonised colours') were introduced in March 2004 (to harmonise across the EU), therefore installations may be entirely of the 'old' or 'harmonised' colours, or, where an 'old' installation has been extended after April 2006, of mixed colours.
Cables with solid cores should never be reused - although during installation they will be bent to fit, these cables are not designed to be flexed and repeated flexing to suit different routes will weaken the cores leading to weak points which could overheat leading to failure.
Twin core and earth
(general internal power cables)
As the name describes, there are two inner cores of insulated solid copper with a bare copper earth conductor between them and covered by an outer PVC sheath - the colour of the sheath may vary between manufacturers, it has not reflection on the quality of the cable. The colours of the cores are:
| Harmonised | Old colour | |
|---|---|---|
| Live | Brown | Red |
| Neutral | Blue | Black |
| Earth | Green and Yellow ( see note) | |
Note:
The earth core in the cable is normally just bare copper, during installation this needs to be inserted through a Green and Yellow sleeve where the earth is connected to a fitting or appliance.
The sizes used to identify multi-core cable refer to the cross sectional area of each conductor and this reflects the maximum current the cable can safely carry 'in free air' - i.e. installed so that the heat generated by the current passing along the cable can dissipated into the surrounding air.
The standard sizes of twin core and earth cable are:
| core size mm2 | current (A) *see note |
wattage (kW) at 240v *see note |
typical applications |
|---|---|---|---|
| 1.0 | 14 | 3.25 | lighting |
| 1.5 | 18 | 4.25 | lighting |
| 2.5 | 24 | 5.75 | power circuit |
| 4.0 | 32 | 7.75 | power circuit, shower |
| 6.0 | 40 | 9.75 | shower, cooker |
| 10 | 53 | 12.9 | cooker |
Note:
The current and wattage figures need be de-rated where cables are run through trunking, under insulation or in any other way which inhibits free dissipation of the heat generated.
3-core and earth
(normally used for the connecting switches/lights to give two way switching)
This type of cable has three inner insulated cores of solid copper with a bare copper earth conductor between them and covered by an outer PVC sheath. The colours of the cores are:
| Harmonised | Old colour |
|---|---|
| Grey | Blue |
| Black | Yellow |
| Brown | Red |
| Green and Yellow ( see note) | |
Note:
The earth core in the cable is normally just bare copper, during installation this needs to be inserted through a Green and Yellow sleeve where the earth is connected to a fitting or appliance.
Standard '3 core and earth' cable is sized:
| Core size mm2 | current (A) *see note |
wattage (kW) at 240v *see note |
| 1.0 | 12 | 2.75 |
Note:
The current and wattage figures need be de-rated where cables are run through trunking, under insulation or in any other way which inhibits free dissipation of the heat generated.
Using cables of different colours
The new, harmonised colours were introduced in April 2004.
However there was a two year period following this (to the end of March 2006) in which new installations could have used either the 'old' or 'harmonised' coloured cable (but not mixed). Any extension to an 'old' colour installation carried out during this period should have been done using 'old' colour cable.
After the start of April 2006, cable with the 'old' colours was not allowed to be used either for new installations or making changes to existing ones.
This obviously presents potential confusion where 'old' wiring is extended or partially replaced using 'new' colour cable. Any installation where 'old' and 'new' colour cables are mixed, must have a caution label (as right) attached to the main consumer or distribution unit of the installation as a caution to any electrician working on the installation.