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    Electric cable and flex


    Although cable and flex may look similar they are used for different purposes. Cable is used for wiring electrical circuits while flex is used to connect electric appliances and lamps to electric circuits. Both consist of a protective PVC sheath that holds a number of cores (the metal conductors that carry the electric current). Each core will have a colour coded PVC cover (although the earth core in electric cable is often bare requiring yellow-and-green sleeving to be fitted).


    Cable

    The most common cable will have three cores and is called two-core-and-earth cable. From 1st April 2006 the colour-coding system for core sheaths in electric cable changed. If planning to carry out some wiring work you will need to use cable with the new colour coding system when it is more than likely that wiring in your house may have the old colour code system, so it is important to know both colour coding systems.

    New colour code system for cable cores

    • Brown is Live
    • Blue is Neutral.
    • Earth will be a bare wire that needs fitting with yellow-and-green sleeving.

    If the cable has four cores (used for two-way switching) the colour coding will be:

    • Brown*
    • Black*
    • Grey*
    • Earth will be a bare wire that needs fitting with yellow-and-green sleeving.

    *Any or all may be live.

    New two-core-and-earth.

    New three-core-and-earth.


    Old colour code system for cable cores

    • Red is Live.
    • Black is Neutral.
    • Earth will be a bare wire or may be fitted yellow-and-green sleeving.

    If the old cable has four cores as used for two-way switching, the colour coding will be red, yellow, blue (any or all may be live) and a bare earth wire.

    All new wiring work must be carried out using cable with the new colour coded system. But it is not necessary to change existing cables.

    Old two-core-and-earth.

    Old three-core-and-earth.


    Cable sizes

    Cable comes in different sizes and is classified by the area of the cross-section of the cores and can range from 1mm2 to 10mm2. The size of the cable you require depends on the current supplied by the circuit. Below is a list of common cable sizes and what they are used for. If you are not sure what size of cable you need, seek advice from a professional electrician.


    Two-core-and-earth

    1mm2        Lighting circuits

    2.5mm2 

    Storage and immersion heaters plus ring main circuits

    4mm2

    Radial circuits with a 30amp fuse

    6mm2

    30amp 12kW cooker circuit or 45amp 8kW max shower circuit

    10mm2

    Cooker circuit above 12kW or shower circuit above 8kW

    Three-core-and-earth

    1mm2    

      Two-way switch wiring

    Flex

    As mentioned above flex also comprises PVC sheathing that protects colour-coded insulated conductors or cores. The PVC sheath of standard flex can be damaged if it comes into contact with a hot surface, there fore portable appliances that produce high levels of heat such as an electric iron or toaster, may well be fitted with rubber sheathing heat-resistant up to 85°C or a braided flex.

    The cores in three-core electric flex are colour coded as below:

    • Brown is Live
    • Blue is Neutral
    • Yellow-and-green is Earth

    The cores in two-core electric flex are colour coded as below:

    • Brown is Live
    • Blue is Neutral

    Three-core flex. 

    Two-core flex.


    Flex sizes

    Flex comes in different sizes and the size you need is dependent on the appliance you are wiring and the wattage (the amount of electrical power expressed in watts) of the appliance. Below is a list of flex sizes and what they are used for. If you are not sure what size of flex you need, seek advice from a professional electrician.

    Two-core (live and neutral) flex

    For non-metal light fittings and double insulated appliances such as some power tools.

    0.5mm2        Up to 700W with a lampshade weight of up to 2kg
    0.75mm2 Up to 1.4kW with a lampshade weight of up to 3kg
    1mm2Up to 2.3kW with a lampshade weight of up to 5kg

    Three-core (live, neutral and earth) flex

    Use for all appliances that need to be earthed.

    0.75mm2      For appliances up to 1.4kW
    1mm2 For appliances up to 2.3kW 
    1.25mm2 For appliances up to 2.9kW 
    1.5mm2For appliances up to 3.6kW 

    There is also 1.5mm2 heat resistant flex for use with immersion heaters.


    Three-core curly flex

    This type of flex is used when it is necessary to keep the flex neat and tidy. Curly flex is available in the same sizes as three-core flex.

    TV, phone and computer cables

    • Television and radio wiring uses coaxial cable, which is capable of transmitting at a high frequency.
    • Telephone cable contains six colour-coded conductors.
    • Computer networks require Ethernet cable and modem cable.


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