box fill requirements

[elecmen]

When calculating box fill for a box that lists the number of conductors on the box do you deduct the 1 ground wire for all and each device(2 conductors) from this number or is that already calculated with the box cubic inch including devices. I say you need to deduct the devices (2 each) and 1 ground wire from the total on the box. My co worker says the numbers in the box already include the devices deducted. What say you?

 

[JFletcher]

You make one total deduction for the largest EGC. If you have #14/2 NM entering a box, the grounds one deduction in total, no matter if there are 1 or 4. Devices are 2 each, and they arent already included or figured into box fill either.

 

[infinity]

When calculating box fill for a box that lists the number of conductors on the box do you deduct the 1 ground wire for all and each device(2 conductors) from this number or is that already calculated with the box cubic inch including devices. I say you need to deduct the devices (2 each) and 1 ground wire from the total on the box. My co worker says the numbers in the box already include the devices deducted. What say you?

What if the box doesn't contain a device?

 

[480sparky]

............ My co worker says the numbers in the box already include the devices deducted. What say you?

I say your coworker is misinformed.

How does he calculate a 4-square box fill? With one device? Suppose there's two?

 

[jumper]

Your co-worker needs to review 314.16(B).

 

[kwired]

Those wire fill figures are for convenience - the total volume is also normally marked. The manufacturer doesn't know if you will have a device installed or not, they just give you total volume of the box, you must figure it in yourself if you use a device in the box.