How to Cap Electrical Wires

1. Turn Off the Power

   Turn off the power to the circuit at the electrical service panel. For added safety, run a strip of electrical tape across each circuit breaker switch involved with this project. The tape is a signal that prevents anyone, even you, from accidentally flipping on the circuit breaker.

2. Install an Electrical Box

   Install an electrical box near the terminated electrical cable. Be sure to install the box in a location that will allow you to pull at least 6 inches of cable through the box.

3. Prepare the Bare Ends of the Wires

   Pull the cable into the back or side of the box. Rip back and remove the outer sheathing. With the electrical wire stripper, cut off any bare ends of wire down to the wire coating to tidy them up. Strip the plastic coating off the ends of the wires. Make sure that you have about 1/2-inch of clean, straight wire at the end.

4. Place Wire Nuts on the Wires

   Turn the plastic wire nuts (also called wire caps) onto the ends of the wires. Turn the wire nut clockwise. Use the appropriate size of wire nut for the wire. Wire nuts that are too big will not sufficiently grip the wire and will fall off. Wire nuts that are too small may initially feel like they are on the wire, but they, too, may fall off.

   Tip

   Bare copper ground wires do not need to be capped. Similarly, BX cable's metal armor sheathing, which conducts to ground without the need for an additional ground wire, may be left alone.
   

5. Add Electrical Tape to Individual Wires

   Tape each wire nut onto its respective wire with electrical tape. The tape is used only to secure the wire nuts. It is not used for insulating bare wire ends.

6. Push the Wires Into the Box

   Push the wires back into the box. Check to make sure that your assembly has not come apart before proceeding to the next step. Any exposed copper wire may cause an electrical short or fire.

7. Add the Blank Wall Plate to the Box

   Attach a blank wall plate to the electrical box, using the provided screws. Some blank wall plates can be painted over.

   If the terminated wires are part of a working circuit, it is now safe to restore power to the circuit. If the terminated wires comprise an entire circuit alone, there is no need to turn on the circuit.

When to Call a Professional

Instead of adding a junction box mid-wall or mid-ceiling, it's cleaner to strip back the wires upline to its starting point: the circuit breaker at the service panel. It can be a safer solution, too, because fewer live wires reside in the wall.

Unless you are experienced at DIY electrical repairs, it's often safest to have a certified electrician work with electrical cables at the service panel junction point.