I want to connect a wire to get power for for a ceiling fan to an existing junction box in the attic that is used right now only for a smoke detector. Box currently has a 12-3 wire coming in, and the smoke detector wires (connected to a quick disconnect). Plastic box says it can take 8 12-gauge wires. How do I count the three smoke detector wires (white, black, red, smaller than 12-guage)? What's my total count so far, and can I add another 12-2 wire?
For box fill calclations, you start with cubic inches...different wires take different amounts of space.
- 18 AWG wires take 1.5 cubic inches
- 16 AWG wires take 1.75
- 14 AWG takes 2.00
- 12 AWG takes 2.25
- 10 AWG takes 2.50
- 8 AWG takes 3.00
- 6 AWG takes 5.00 cubic inches
Larger wires require special engineering.
all grounds are broken out and count only as 1 of rhe largest ground wire.
All cable clamps together count as 1 of the largest wire clamped.
If there is a yoke (mounted piece of equipment in the box), that counts as 2 of the largest wire going to it.
You have to total up the cubic inches and make sure the box is big