4 gang fill capacity


Old 03-04-02, 08:06 AM
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Question 4 gang fill capacity

I have a 4-gang Carlon new work box that will house four 3-way switches. The box volume as inscribed on the box is 60 cu. in. and has a wire fill capacity of 26 12 AWG wires. I have four 12/3 and three 12/2 romex cables in the box and I believe I am exceeding the wire fill capacity of the box and would like some suggestions on how to avoid this problem.

Three of the 12/3 cables go to a 3 gang box at the other end of the room that contains the three other 3-way switches. Cables carrying power to the light fixtures for all three switches come out of the other 3 gang box (which has a wire fill capacity issue as well). The other 12/3 wire goes to a different box. One 12/2 wire is power in, the second is power out to other devices, and the third is power to one of the fixtures being controlled by one of the 3-way switches.

My wire fill calcs:
12 (three conductors for each of the four 12/3 cables)
6 (two conductors for each of the three 12/2 cables)
1 (ground for all)
1 (cable clamp for all)
8 (two conductors for each of the four 3-way switches)
28 total conductors x 2.25 = 63 cu. in. (which is over the capacity of the box)

Are my calcs correct? Does anyone have any suggestions on how to reduce the number of conductors? Since three of the 12/3 cables lead to the same box on the other end and since the neutral for all three will be connected together, can I run one 12/3 and two 12/2 cables instead of three 12/3 cables to the other three 3-way switches? Are there extension rings available that increase the volume of 3 and 4 gang boxes?

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Old 03-04-02, 04:52 PM
Join Date: Feb 2002
Location: port chester n y
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I suggest using a"deep" metal gem box which can be "made" into any number of gangs.You'll avoid 4 grounding leads to the switches.Also try to re-arrange the wiring so each gang,or switch,has a 12/3 and 12/2 "standard" connection.The 12/2 (at each switch or gang) goes to the controlled fixture.The 12/3 is from the "first" 3-way and has 2 "pivots" (Red & Black) and the neutral (White). The 2 Whites splice together and the Black of the 12/2 and the Red & Black of the 12/3 terminate on the switch.A 4-gang box with 4 3-ways can get complicated !! Good Luck!

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