It is the responsibility of the user of this information to know and understand the NEC (National Electrical Code) as it applies to them, as well as any local regulations or laws that may pertain. While many jurisdictions do adopt the standards of the NEC, some may have requirements in addition to, or exemptions from those standards. The information on this page is intended to aid in electrical wiring projects that become necessary when doing DIY home improvements and repairs. We cannot assume responsibility for personal injury or property damage as a result of using the information provided here.
When doing remodeling work it may be necessary to splice wires to relocate circuits and add new devices. A splice is the joining of two or more wires by twisting them together to a point. A plastic fastener, known as a wire nut, is used to insulate and secure the splice. Use wire nuts with metal rather than plastic threads and choose a size appropriate for the conductor gauge you're using.
Splices should only be made inside an electrical box known as a junction box. A junction box is a square electrical box. Electrical boxes are made of metal or plastic and come in 3 basic shapes. 1. A junction outlet box is square and used to house splices. 2. A device box is shaped like a rectangle and is used to house wall switches and receptacles. 3. A fixture box is octagonal or round and is used to house a ceiling or wall fixture like a light or fan.
According to the NEC there is a limit to the number of conductors allowed inside an outlet box depending on the gauge you're using and the depth of the box. While wires are conductors they aren't the only ones in an electrical outlet. The switches and receptacles are also conductors and they add to the total present in the box. All metal parts must be added to determine how many conductors you will have in the final installation. For a complete list of all the possible conductors and how much they add to the total check the NEC which should be accessible at a public library.
An outlet box has several holes in the sides and back with removable plugs. Choose holes conveniently located for the cables to be spliced and remove the plugs. Use a clamp collar for each one and loosen the screws to open it. Pull about 8 to ten inches of cable through the clamp and tighten the back down collar around the cable. Insert the clamp into the holes and from inside the box, push the included nut over the wires and onto the clamp threads. Turn the nut onto the threads and use a screwdriver point and hammer to tap it down until tight.
Split the plastic sheathing on the cable starting about 6 inches from the end leaving at least 1/2" of the plastic sticking out of the clamp. Cut the sheathing to remove it and strip off about 3/4 inch of the plastic insulation from the end of each wire without touching the copper.
The best way to remove the insulation without nicking the copper is to use a wire stripper. Most strippers have a set of cutters for the most common gauges. Gently twist the strippers back and forth a couple times and pull the insulation straight off the end.
Hold the wires together so the ends match up and twist them together in a clockwise direction using lineman pliers. Make 2 or three turns to form a solid union.
If the ends of the wires are too far apart the nut won't work, so be sure the ends match up before twist them. If necessary snip off a bit at the tip to get them even so the connector goes on properly.
Thread the wire nut clockwise onto the twisted conductors being sure no bare copper is exposed at the bottom. Pull gently on the connector to be sure it's secure. You can wrap electrical tape around the wires and cap for extra security or just push the wires into the back of the box and attach the cover.