understanding code: box fill

Old 11-06-03, 08:37 AM
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understanding code: box fill

I'm trying to figure out what junction box to use for a ceiling fixture. There is presently no box, and I have limited space (depth and width, in particular).

The box will contain:
--one 12/2 conductor, probably clamped inside the box
--wires for the light, including hot, neutral, and stranded ground
--a mounting strap for the light
--a pigtail for grounding the strap
--wire connectors (3--hot, neutral, ground)

Based on 314.16, how many volume allowances is this? How do you count it?

Also, is there any problem using a rectangular box for a ceiling fixture. I understand that 314.27 specifies that boxes used for lights shall be designed for that purpose. Do rectangular boxes qualify?
Old 11-06-03, 11:33 AM
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The "12/2" counts as 2.
The "wires for the light" count as 2.
All the grounding wires taken together count as 1.
The interior clamp counts as 1.
The mounting strap doesn't count (it's outside the box).
Pigtails don't count.
Wire nuts don't count.

That's a count of 6. Multiply that by 2.25 for 12-gauge wire and you get 13.5 cubic inches. Almost any box will do.
Old 11-06-03, 04:39 PM
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A rectangular box that uses 6/32 screws for attachment of the fixture is limited to a wall type installation and a fixture that weighs less than 6 pounds.

Use a round 8B box instead. They use 8/32 screws.
Old 11-06-03, 05:34 PM
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Or use a square box with a round ring. Round rings are tapped for 8/32 screws. Same weight limits as an 8B, more knock outs to choose from.

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