Three Core and Earth

Electric wiring can be categorised according to its voltage, phase, nature of electric signal, type and design of cable and its circuit design. The three core and earth system consists of three inner insulated cores of solid copper and a bare copper earth conductor, all of which is covered by a protective PVC sheath. The colours used for wiring in the UK are now grey, black , brown and the green/yellow. Insulation is provided for the earth connection only when it is exposed to make connections. The three core and earth configuration is used for single insulated appliances which must have an earth connection. However, its most common use is when lights need to be turned on and off from different locations. This two-way switching requires extra connections and the three core and earth provides the necessary extra conductor. The 'Common' system is that switches are connected to each other by a pair of wires called strappers. The switches are called single pole, double throw (or SPDT). Three core and earth is mainly used for hallways, stairwells, bedrooms and particularly long corridors in domestic residences. It is also found in commercial complexes where many rooms or offices might line a long corridor.

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