National Electrical Code: Number of Wires in a Box

Learn about the National Electrical Code for wiring. Find tips and information on counting wires in electrical boxes, number of conductors allowed in a wiring box, and more.
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Placing too many wires into an electrical box is difficult, dangerous, and against the National Electrical Code. To avoid possible shorts and overheating due to tightly packed wires, the code limits the number of wires you can put into an electrical box. Wires aren't the only things that count as wires, however.

Counting Wires in Electrical Boxes

Each item in your electrical box counts as a different amount of wires. Each insulated wire, all cable clamps combined, all uninsulated wires combined, and each support for light or other fixture count as one wire. Each switch, outlet, or other device counts as two wires. Jumper wires, however, count as zero wires. 

Number of Wires in a Switch Box

The switch box shown has a total of eight "wires" — one for each of the four insulated wires, two for the switch, one for all of the bare ground wires, and one for the cable clamps. The jumper wire does not count as a conductor. You'd need a 3x2x3-1/2-inch device box if you were wiring with 12-gauge wire.

Number of Conductors Allowed in a Wiring Box

This chart designates the number of conductors allowed in a wiring box based on your box size, the type of box, and the wire size.

2 Comments

  1. Actually that box has a total of 6 wires. It has two neutral, hot, and two ground. There is one long and one short ground. The short ground is twisted onto the long ground which is routed through the twist ground connector. Now one big mistake is that there are actually only FOUR CONDUCTORS within that box.

    IAW NEC 314.16 (B) (1) Exception: An equipment grounding conductor or conductors or not over four fixture wires smaller than 14 AWG, or both, shall be permitted to be omitted from the calculations where they enter a box from a domed luminaire or similar canopy and terminate within that box.

  2. Your switch box example shows 7 wires not 8.

    1. nvm my miscount. ignore that LOL


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