NEC 314.16 (B)(4) Question

[midnightprogrammer]

I have a double gang box (34 cubic in capacity) with (2) 14/3 and (2) 12/2 separate circuits that will house (2) switches.

The question I have has to do with the wording on 314.16 (B)(4) as to the allowances taken for the Devices in the box. One of the switches will have #14 AWG conductors, the other will have #12 AWG conductors.

I believe this is how the box fill calculation should turn out....

So....
6 #14 @ 2.0 = 12 Cu In
4 #12 @ 2.25 = 9 Cu In
1 Gnd @ 2.25 = 2.25 Cu In
1 Clamp @ 2.25 = 2.25 Cu In
1 Dev @ 2 * 2.0 = 4.00 Cu In (Here's where the question comes in)
1 Dev @ 2 * 2.25 = 4.50 Cu In (Here's where the question comes in)

Totaling 34 Cu In.....

Did I do it right or have I overfilled the box?

Thanks

 

[C3PO]

Your box fill calculation looks right to me.

 

[480sparky]

Looks good from my truck.

 

[chris kennedy]

Whats up with the clamp? Test or practice question?

 

[midnightprogrammer]

NEC 314.16 (B)(4) Question

The clamp deduction is from the NEC rule 314.16 (B)(2), if I'm reading the rules right says:

(2) Clamp Fill. Where one or more internal cable clamps,
whether factory or field supplied, are present in the box, a
single volume allowance in accordance with Table 314.16(B)
shall be made based on the largest conductor present in the
box. No allowance shall be required for a cable connector with
its clamping mechanism outside the box.

So....
I deduct 1 for all the clamps in the box.
I'm using the Carlon Zip Blue boxes that have the internal clamps built-in.

I'd rather not take the deduction (since sometimes I could use the extra volume) but I'm also trying not to give the inspectors any reasons to flag a problem as I'm wiring a 2 story addition on my house myself. I just don't have a good feeling on how picky the inspector is going to be when he comes to look at the rough electrical.

 

[iwire]

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