Capping off electrical wires is necessary to safely remove a device from a circuit. A wire capable of being made hot by turning on a circuit breaker or replacing a fuse needs to be capped off if not connected to a load or some electrical device. An energized wire is a shock hazard to a person making contact with it. An energized wire is a fire hazard, arcing over between the hot wire and a grounded surface will ignite the combustible material around it. Capping off a wire takes five minutes but it could save your life or the life of someone else.
Step 1
Turn the circuit breaker off or remove the Edison base fuse from the circuit that you will be capping off. Professional electricians cap off wires while they are hot as a routine procedure, but it's not something that the beginner should attempt.
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Step 2
Cut back the ends of the wires until they are flush with their insulation so that you will be working with a perfectly straight section of conductor. Remove an inch of insulation from the end of the wire to be capped using the wire strippers.
Step 3
Screw a wire nut tightly over the stripped conductor. Holding the wire tightly in one hand, tug on the wire nut with the other to make sure it holds. Once you have a wire nut firmly in place, tape over the wire nut and wire for extra assurance that it won't come loose.
Step 4
Repeat steps 2 and 3 until you have capped off all the wires. If the wires you capped off are in a device box, a lighting outlet box, a pull box, or a junction box, install a blank cover on the box. Covering device boxes, lighting outlet boxes, pull boxes, and junction boxes is required by the National Electrical Code.