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I have 3 hall luminaires controlled by a 4-way switching system. The electrician elected to run 14-3/G NM too all the fixtures. The most distant one is mounted on a round 4 inch x 1/2 inch pancake box. The capacity is marked 6 cu in. The red lead is in the box, but it is capped with a wire nut and not otherwise used. Does it count for 2 cu in like the black and white leads or does it count for 1 cu in like the ground because it is 'dead.'

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The manufacturer suggests that the luminaire can be installed using only the central 1/8" IPT hole in the crossbar as long as the 1/8" nipple carries a lock washer and nut to fix it to the crossbar and a lock washer and nut secure the fixture to the nipple. Clearly the electrician had difficulty using the matching round head machine screws that can be installed in the threaded hole in the crossbar and the matching hole diagonally opposite it. Getting all 3 supports to line up is challenging.

Can I use only the nipple and meet code?

Are the missing knockouts a violation?

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  • 1 unit per black wire.
  • 1 unit per red wire.
  • 1 unit per white wire.
  • 1 unit for grounds.
  • 1 unit for stud or hickey (if that's what you're going to use to attach the fixture).

That's 5 total units, times 2 cu. in. per unit (since you're using 14 AWG conductors). That's a total of 10 cu. in., which is well over the 6 cu. in. the box is rated for. Even if you attach the fixture directly to the box, the fill calculation would be 8 cu. in.

NOTE: Above count is based on a single conductor of each color. If there are more than one, you have to count one unit per wire.

It makes no difference if the wire is live or not, all conductors that enter the box are counted.

And yes, according to 314.17(A) the unused knockouts should be closed.


On a side note. Grounding conductors don't count for 1 cu. in., they count as 1 unit. That unit is then multiplied by the value from Table 314.16(B), based on the largest conductor in the box. So in your example, all the grounds require 2 cu. in., because you're using 14 AWG conductors.

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    Other than ground wires you count each wire. I see at least 3 white wires 2cu in X 3 = 6 with a 6 cu inch box you are way over filled right there. if the fixture wire is smaller than 14 it can be omitted but then you still have a ground and red how many blacks? Agree with @tester101 that the openings must be closed.
    – Ed Beal
    Feb 11 '16 at 19:50
  • @EdBeal You're right. After a closer look, it does appear that there's more than one of each color wire.
    – Tester101
    Feb 11 '16 at 20:06
  • The only comfort is the electrician wasn't a 12 AWG freak.
    – bib
    Feb 11 '16 at 22:54

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