Mistake 8: Overfilling Electrical Boxes
Mistake: Box too small
Too many wires stuffed into a box can cause dangerous overheating, short-circuiting and fire. The National Electrical Code specifies minimum box sizes to reduce this risk.
Solution: Install a larger box
To figure the minimum box size required, add up the items in the box:
1 - for each hot wire and neutral wire entering the box
1 - for all the ground wires combined
1 - for all the cable clamps combined
2 - for each device (switch or outlet—but not light fixtures)
Multiply the total by 2.00 for 14-gauge wire and by 2.25 for 12-gauge wire to get the minimum box size required in cubic inches. Then choose a box with at least this much volume. Plastic boxes have the volume stamped inside, usually on the back. Steel box capacities are listed in the electrical code. Steel boxes won’t be labeled, so you'll have to measure the height, width and depth of the interior. Then multiply to find the volume.