A common cause of electrical faults is an incorrectly wired plug. Wiring a plug is not difficult however it is important to get it right.
You will need a few basic tools. If you are just replacing a damaged plug you will probably only need a screwdriver. If you need to strip back the insulation and trim the wires you will also need a sharp knife and side cutters, or a wire stripping tool.
If you are starting with a new cable, you will first need to cut off about 4cm of the outer insulation. There are various methods, but probably the easiest and safest way to do this without damaging the internal coloured wires is to slit the outer insulation of the cable lengthways and then peel away and cut off.
Separate the wires and use the plug as a gauge to cut the wires to the correct length. Leaving the wires the same length usually results in the live and neutral wires becoming crushed when the plug cover is replaced. The plug is also designed so that the live (brown) is the shortest and tightest wire in the plug. This ensures that the live wire is the first to disconnect should the cable be pulled out of the plug. Similarly, the earth wire is the longest to ensure it is the last to disconnect.
Remove about 5mm of insulation from the end of each wire. The easiest way to do this is to use wire strippers. Alternatively you can use normal side cutters, but you need to be careful not to cut into the individual strands of wire. Tightly twist the ends of the wires.
The plug has markings inside to identify each pin:
- (L) = Live = Brown
- (N) = Neutral = Blue
- (E) = Earth = Yellow & Green
Old appliances (pre-1971) may have a cable with different colours:
- (L) = Live = Red
- (N) = Neutral = Black
- (E) = Earth = Green
If the plug has screw type cord clamp, remove or loosen this first. Connect each wire to the correct terminal. Slacken the screw and push the bare wire into the hole and then re-tighten the screw. It’s often easier to push the pins up slightly when connecting the wires. Starting with the earth, then neutral and then live is usually the easiest order for wiring the terminals.
Check the wiring is correct and all the terminal screws are tight. Loose screws can cause overheating.
Tighten the cord clamp over the cable. Make sure the cord clamp is gripping the outer insulation of the cable, not the coloured wires. For non-screw type clamps you may need to adjust the clamp to suit the size of cable. Test the cable is secure by giving it a sharp tug.
Check that the correct fuse is fitted. The fuse rating recommended by the manufacturer should always be used. If the original fuse size is not known, the recommended method is to use the 700W rule. For appliances below about 700W a 3A fuse is generally used. For appliances above 700W, a 13A fuse may be used. The maximum power consumption in WATTS (W) of the appliance will be marked on the rating plate/label.
We have separate article on selecting the correct fuse size.
Make sure there are no loose strands of wire in the plug. Check the wires are laying in the correct channels and will not become crushed when the cover is replaced. Double check that the wires are in the correct terminals and then replace the plug's cover and tighten the screw. If the plug has a cardboard wiring diagram over the pins, make sure this is removed before using the appliance.
Some appliances will only have two wires - live & neutral. These are 'Double Insulated' and do not rely upon the earth wire for protection. The plug is wired as above but there is no earth wire to connect, however make sure that the screw on the earth terminal is not loose.
For companies and organisations that need to ensure their staff have the skills and competency to correctly wire a plug, we run a plug wiring course. We can also combine this with a PAT testing course.
