Thread: Volume of JB vs # of conductors

Well, folks....I've passed 3 of the 4 ICC exams to get my Residential combination inspector certification....just have electrical left....I'm ready to just cry.....Anyways, here below is an ICC practice exam question. I could not figure out how they got their answer any help is appreciated, as usual!

Given: A junction box that has the following combination of conuctors entering the box:

- 4 #10AWG current carrying conductors.
- 4 #12AWG current carrying conductors.
- 2 #10AWG and 2 #12 equipment grounding conductors conductors.
- 2 internal clamps.

What is the minimum volume of the box, in square inches, required?

A) 24.0
B) 28.5
C) 32.5
D) 33.0

The answer is (A). I looked at e3805.12.2.3, e3805.12.2.4, and e385.12.2.5 as well as table e3805.12.2.1. I just don't come close to any of the answers so what am I doing wrong! A step by step analysis would be appreciated.

Thanks for your help!

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- 4 #10AWG current carrying conductors.
- 4 #12AWG current carrying conductors.
- 2 #10AWG and 2 #12 equipment grounding conductors conductors.
- 2 internal clamps.

Here is my answer, and how I calculated:

Each #10 = 2.5 per conductor ---------(10)
Each #12 = 2.25 per conductor --------(9)
All grounding =1 at largest value -------(2.5)
All clamps = 1 -------------------------(2.5)

Total = --------------------------------(24)

Dom.