Introduction
Electrical current is carried around your home to appliances in cables and flexes that contain a minimum of two ‘cores’. Each core is made of copper wire and surrounded by colour-coded insulating plastic. The individual cores are then bound together into the cable or flex by further insulating plastic.
It is important to use the correct type and size of cable, or flex, for the job in hand. Their size is expressed in mm˛ which refers to the area of the cross-section of the individual cores within the cable or flex. The greater the cross-section, the more current that can flow safely through the wires.
Electricity is dangerous!
Current building regulations, from 1st January 2005, clearly state that only certified persons can carry out electrical installation work, or the work must be certified upon completion. All electrical wiring and installation data given on SimplifyDIY.com is for information purposes only.
Cable
Fixed wiring that is usually hidden in walls, floors and ceilings is done using cable, which is oval in cross-section and contains three or four wires.
Bear in mind that the wire colours given below are for new cables, as determined by the IEE Wiring Regulations from March 2006 onwards. For more details on these changes and how to connect new cables to old ones, see…
Two-core-and-earth cable
(also called twin-and-earth), a bare earth core is sandwiched between a sheathed live (brown) and neutral (blue) wire.
Three-core-and-earth cable
a bare earth core lies with three sheathed wires, any or all of which can be live, in brown, black and grey. These cables are used for two-way lighting circuits, where a light fitting is controlled by two switches, for example at the top and bottom of a staircase.
Single core cable
is most often used in industrial applications, but may be required domestically for earth bonding. In the case of earthing wire, this is a single wire, surrounded by yellow and green insulating plastic.
Circuit | Cable Size (mm˛) | Fuse (Amps) | Max Area (m˛) | Max Cable Length (m) |
Ring Circuit (sockets) | 2.5 | 30 or 32 | 100 | 50m with MCB, 60m with cartridge fuse |
Radial Circuit (sockets) | 2.5 | 20 | 50 | 33m with MCB, 35m with cartridge fuse |
Radial Circuit (sockets) | 4.0 | 30 or 32 | 75 | 33m with MCB, 38m with cartridge fuse, rewirable fuse not permitted |
Spurs | 2.5 | - | - | Not to exceed maximum of ring or radial circuit |
Lighting Circuit | 1.5 | 5 or 6 | - | Maximum of 1200W, ie 12x100W bulbs |
Immersion Heater | 2.5 | 15 or 16 | - | - |
Electric Shower | 10.0 | 45 or 50 | - | Requires own dedicated circuit |
Electric Cooker | 6.0 | 45 or 50 | - | Requires own dedicated circuit |
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When connecting the earth core into sockets and switches, you should cover any bare lengths of it with green and yellow sheathing, available from electrical suppliers.
Note that steel-wire-armoured (SWA) cable must be used in exterior installations to ensure the wire is frost-resistant..
Flex
Portable appliances and lights are connected to the fixed wiring system with flex, which is round in cross-section and contains two or three wires.
In a two-core flex, there is a sheathed live (brown) and neutral (blue) wire. These flexes contain no earth wire and should therefore be used only to connect double insulated appliances, carrying the symbol shown on the left.
In a three-core flex, the sheathed live (brown) and neutral (blue) wires are accompanied by an earth wire (yellow and green). Ensure you use special high temperature flex for immersion heaters and storage heaters.
Max Wattage (W) | Flex Size (mm˛) | Amps (A) |
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Further information and useful links
