Junction Box Fill

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jeff48356

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Location
Livonia, Michigan
I'm running a 60A feeder for power out to a detached garage, with additional wiring for a 3-way switch for the outdoor lights on it. The junction box in the basement where it connects to the 1" PVC conduit to go to the garage would need 44.5 cubic inches to hold 6 #6 conductors, 3 #14's for the 3-way switch, and a #10 ground that counts as all one conductor.

The question is, since the #14's are two travelers and a common, would I be able to eliminate two of them (one of the THWN's in the conduit and one in the Romex) from the count since only one traveler can carry current at any given time? If so, I would only need to count both travelers as one conductor, plus the common. That would bring it down to 40.5 cubic inches, where a 4-11/16" square box is rated for 42 cubic inches.

If not, what's the next size up in junction boxes that I could use?
 
Here is the Note to table 310.15(B)(3)(a). IMO, one wire from the 3 way can be excluded for conduit fill but not for jb sizing. The size of the jb has nothing to do with current carrying conductor's.

1Number of conductors is the total number of conductors in the
raceway or cable, including spare conductors. The count shall be
adjusted in accordance with 310.15(B)(5) and (6). The count shall not
include conductors that are connected to electrical components that
cannot be simultaneously energized.
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Use a 4 11/16" box with an extension box.

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Dennis Alwon said:
Here is the Note to table 310.15(B)(3)(a). IMO, one wire from the 3 way can be excluded for conduit fill but not for jb sizing. The size of the jb has nothing to do with current carrying conductor's.
Click to expand...

I disagree. The wire can be excluded for ampacity adjustment purposes but not conduit/box fill. The wire is still taking space.

Personally I would use a 664 or 884 can vs a 4-11 box.
 
curt swartz said:
I disagree. The wire can be excluded for ampacity adjustment purposes but not conduit/box fill. The wire is still taking space.

Personally I would use a 664 or 884 can vs a 4-11 box.
Click to expand...


You are correct, my wording was poor. I meant it can be excluded for de-rating in the conduit as a current carrying conductor. Thanks
 
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