Replacing a three prong electrical plug is essential if the plug becomes damaged in any way. Damaged plugs are not only shock hazards, but could also cause a fire if the wires short together. As such, they should be replaced as soon as any damage is noticed. As well as the standard live and neutral wires, three prong plugs also have a ground wire to protect from electric shock hazards with faulty appliances. If the ground wire is present, it should always be connected.
Cut off the old plug with wire cutters and discard, if you are replacing an existing plug. Remove the cover from the new plug, and slide the electrical cord through the hole. Using the utility knife, carefully cut off three inches of the outer insulation to expose the inner wires. Strip half an inch of insulation off the ends of each of the inner wires.
Tie the wires together with what is known as an "underwriter's knot," close to the bottom of the stripped outer insulation. This provides strain relief, to stop the wires coming free from the connectors if the cable is accidentally pulled.
Twist the strands of wire together at the ends of each of the inner wires, and form each set into a hook shape that can be wrapped around the shafts of the connector screws.
Put the hook on the end of the black (hot) inner wire around the brass coloured screw shaft, and then tighten the screw to clamp the wire in place. The hook on the end of the white (neutral) wire should be wrapped around the shaft of the silver coloured screw, and the screw tightened.
Hook the wire at the end of the green or bare wire (earth) around the screw shaft of the ground connection, and tighten the screw. Inspect the connections and make sure that any stray strands of wire are neatly tucked in to the relevant connector.
Check that all the wires are neatly contained within the plug, and replace the cover. The plug can then be tested in a grounded three slot electrical socket.
Some plugs have a grip to hold the cable in place where it enters the plug. If this applies to your plug, you do not need to tie the underwriter's knot.
Make sure the plug is suitable for the appliance it will be used with. The current and voltage used by the appliance should be less than the maximum specifications for the plug.