DIY Wire Splicing
Also see:When remodeling it may be necessary to splice wires to relocate circuits. This page offers help with wire splicing. Always check the local building code for proper wiring procedures. Turn off electrical circuits before working on wiring.
A wire splice is the joining of two or more wires by twisting them together to form a "pigtail". 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 gauge wire to be spliced. Splices are usually made inside an outlet or junction box. These boxes can be made of steel or plastic and come in 3 basic shapes. 1. A junction outlet box is square and is use to house wire splices. 2. A device outlet box is shaped like a rectangle and is used to house wall switches and receptacles. 3. A fixture outlet box is octagonal or round and is used to house wiring for ceiling or wall fixtures like lights.
There is a limit to the number of wires allow inside a box, depending on the cable gauge and the depth of the box. This is the number of wires inside the cable, for example, 12/2 cable has 3 wires, 2 circuit wires and one ground. New plastic electrical boxes will sometimes have the number of allowable wires stamped on the inside of the box for convenience. The chart below lists the acceptable number of wires per box for some of the most common sizes.
| Box Size and Type in Inches | Maximum Number of Wires Allowed in Each Box for Gauge | ||||||
| ––heigth X width X depth–– | 18 awg | 16 awg | 14 awg | 12 awg | 10 awg | 8 awg | 6 awg |
| 4 x 1 1/2 Octagon or Round | 10 | 8 | 7 | 6 | 6 | 5 | 3 |
| 4 x 2 1/8 Octagon or Round | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 4 x 4 x 1 1/2 Square | 14 | 12 | 10 | 9 | 8 | 7 | 4 |
| 4 x 4 x 2 1/8 Square | 20 | 17 | 15 | 13 | 12 | 10 | 6 |
| 3 x 2 x 2 Device | 6 | 5 | 5 | 4 | 4 | 3 | 2 |
| 3 x 2 x 2 1/2 Device | 8 | 7 | 6 | 5 | 5 | 4 | 2 |
| 3 3/4 x 2 x 2 1/2 Device | 9 | 8 | 7 | 6 | 5 | 4 | 2 |
Splicing the Wires
An outlet box has several holes in the sides and back with removable plugs. Choose a hole conveniently located for the cable to be spliced and remove the plug. Insert a cable clamp in the hole and from inside the box, thread the included nut onto the shaft until tight. Open the clamp collar by loosening the screws and pull about 8 to ten inches of cable through it and into the box. Tighten the collar around the cable.
Split the plastic sheathing on the cable starting about 4 inches from the end. Separate the wires and remove the paper insulator. Strip off about 3/4 inch of the plastic insulation from the wires to be spliced.
The best way to remove the insulation without nicking the copper wire is to use a wire stripper. Most strippers have a set of cutters for the most common household wire gauges. Twist the strippers back and forth a couple times and pull the insulation off the end of the wire.
Hold the wires together and twist in a clockwise direction. Use lineman pliers to twist one or two turns in the wire.
If the wire ends are spread too far apart to accept a wire nut, clip the end of the longer wire.
Thread a wire nut clockwise onto the twisted wires. Test the wire nut by pulling on it to be sure it's secure. Fold the wires into the outlet box and attach the cover.
