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I'm considering buying the following product for a security floodlight install: Arlington 8141-1 Vertical Siding Lamp Mounting Kit with Built-in Box for 1/2 Inch Vertical Siding LAP. It seems to get great reviews, but I don't understand how this can possibly follow code. It features a round, 4in diameter x .5in deep j-box. In the simplest case, it would require six wires to connect a fixture at the end of the cable run (three from the NM cable, three from the fixture). However, six 14-gauge wires would require a 4in round j-box that is 1.25in deep according to NEC.

Can someone please explain to me why this j-box is acceptable or not? Full disclaimer, I'm a total noob at electrical so it's entirely possible I'm just not understanding something properly. Thanks!

  • Whatever canopied lamp you (should) buy will not have 14AWG wire, it will be 16 or less and not count, see below. – Mazura Oct 30 '15 at 1:41
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ecmag.com's interpretation of 314.16(B)(1) Conductor Fill:

There is an exception under the conductor-fill provision that pertains to luminaire (fixture) conductors. An equipment-grounding conductor or four or fewer luminaire (fixture) wires smaller than 14 AWG, or both, entering a box from a domed luminaire (fixture) or similar canopy and terminating within that box, can be omitted from box-fill calculations. Under certain conditions, up to four luminaire (fixture) conductors and one equipment-grounding conductor can be installed but not counted in the box-fill calculation. The conductors must be 16 AWG or smaller and must enter the box from a domed luminaire (fixture) or similar canopy.

I always wondered why the wires on lights are so flimsy; that's why, so you don't have to count them in box fills.

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    Thanks!! So based on the rule you presented, only the three wires from the power source would be counted. Seems like there would be just enough room for them. Is it fair to say that this product is only intended for use at the end of a cable run (ie. I shouldn't connect something else downstream from the fixture, solely using this j-box)? – Ken Oct 30 '15 at 2:47
  • 16 Awg is the smallest allowed by code for UL approved light fixtures. – Kris Oct 30 '15 at 2:51
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    @Ken - Correct. Pancake boxes are maxed-out with a single cable. – Mazura Oct 30 '15 at 2:57

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