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Wednesday, 15 April 2015

Step by step guide to wiring a plug

Wiring a plug is not difficult but you would be surprised how often people get it wrong. A wrongly wired (or fused) plug puts everyone at risk from electric shock or fire. This chapter gives a step by step guide to wiring a plug.

(This is a chapter extract from the Manual of Portable Appliance Testing)

Eight simple steps to a well wired plug:

1. Strip off the outer cable sheathing to expose about 4cm of the insulated wires. A small pair of cutters is useful for this. Use this to nick the outer insulation, taking care not damage the inner wires. Pull back the outer insulation.

2. The inner wires may be twisted, so separate these out. Cut the Live (brown) wire and the Neutral (blue wire) so that they are about 3 cm in length. This will make them about 1 cm shorter than the green/yellow Earth wire.

3. Remove the insulation from the inner wires to leave about 5mm of exposed metal core on each wire (Fig App 2.4). When doing this, take care not to cut into the individual strands of wire. Twist the strands of wire together neatly. The picture here shows the brown wire untwisted.

4. Connect the wires to the correct terminals. The brown Live wire to the terminal on the fuse holder marked L, the blue Neutral wire to the terminal marked N and the green and yellow Earth wire to the terminal at the top of the plug marked E. Class II appliances do not have an Earth wire because they are double insulated, always marked with a double box symbol .

Class 1 (3 wires)

Class II (no earth wire)

5. Fit the exposed metal core of each wire through each terminal and tighten the terminal screws. Ensure that the insulation reaches right up to each terminal and that there are no loose strands of wire.

6. Fit the flex firmly into the cord-grip making sure that the grip fastens on the outer insulating sleeve of the flex.

7. Read the instructions on the appliance to see what rating of fuse is required and fit the correct fuse in the plug. If the instructions are not available, use the gauge of mains flex used and the power rating of the appliance to work out the fuse rating.

8. Fit the plug cover making sure that the inner wires are lying in the right channels, and do not become crushed when the screw is tightened.

Below are some tips that are useful when wiring a plug.

• Don’t strip too much of the outer insulation away, otherwise you will have too much wire inside the plug.

• Keep the Earth wire about 1 cm longer than the Live and Neutral wire as the Earth pin is further away.

• After stripping away the inner insulation, twist the copper wires with your fingers. This will keep all the strands together.

• All the screws need to be well tightened. Loose screws can lead to overheating and are a fire risk.

• Make sure that the wires do not get trapped when the top of the plug goes on.

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