Because of wall depth issues, I need to use gangable metal box to create a "shallow" 3-gang old work box. I am hoping someone can verify a couple things related to box fill for the gangable boxes...
1. Each gang has 2 internal NM cable clamps on them. My interpretation is that when they are ganged together as 1 3-gang box, all 6 internal clamps count as a single conductor. Correct?
2. Total volume is simply 3 times the volume of a single box.
Therefore, the below should be correct assuming the above statements are accurate:
3x2x2.75" gangable box has a 14 cu in capacity based on 314.16a, so total capacity is 42 cu in of 3 ganged together.
I have 3 14/2 NM wires and 3 12/2 NM wires entering the box. Each gang has 2 internal NM cable clamps on them, and I will have 1 switch connecting with 14/2 and 2 switches connecting with 12/2.
For box fill I am looking at:
6 14 conductors
6 12 conductors
1 12 conductor for all cable clamps
1 12 conductors for all grounds
2 14 conductors for 1 switch
4 12 conductors for 2 switches
Therefore in total, I have the equivalent of:
12 12 conductors or 27 cu in
8 14 conductors or 16 cu in
and I come up 1 cu in short of being able to use this box within code.
However, if I remove all of the internal cable clamps and use external NM connectors in the knockouts, I need 40.75 cu in and I am good to go.
Is this accurate?
I was kind of hoping that somewhere in the code it allowed some extra allowance for fill when the boxes were ganged together to pick up that 1 lousy cu in I needed.
any feedback would be appreciated.
1. Each gang has 2 internal NM cable clamps on them. My interpretation is that when they are ganged together as 1 3-gang box, all 6 internal clamps count as a single conductor. Correct?
2. Total volume is simply 3 times the volume of a single box.
Therefore, the below should be correct assuming the above statements are accurate:
3x2x2.75" gangable box has a 14 cu in capacity based on 314.16a, so total capacity is 42 cu in of 3 ganged together.
I have 3 14/2 NM wires and 3 12/2 NM wires entering the box. Each gang has 2 internal NM cable clamps on them, and I will have 1 switch connecting with 14/2 and 2 switches connecting with 12/2.
For box fill I am looking at:
6 14 conductors
6 12 conductors
1 12 conductor for all cable clamps
1 12 conductors for all grounds
2 14 conductors for 1 switch
4 12 conductors for 2 switches
Therefore in total, I have the equivalent of:
12 12 conductors or 27 cu in
8 14 conductors or 16 cu in
and I come up 1 cu in short of being able to use this box within code.
However, if I remove all of the internal cable clamps and use external NM connectors in the knockouts, I need 40.75 cu in and I am good to go.
Is this accurate?
I was kind of hoping that somewhere in the code it allowed some extra allowance for fill when the boxes were ganged together to pick up that 1 lousy cu in I needed.
any feedback would be appreciated.
