Wiring – Does the lighting fixture size change the number of allowed wires in a junction box

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In am working on a 1920s era home. The electrical system in the house has been updated several times in a very hodge-podge way. Originally the house had conduit in the attic going from light receptacle to light receptacle. At a later date, romex was run from those light receptacles to plugs in the walls. Now I am replacing all the old rubber and cloth wire because it is disintegrated.

I recently checked the conductor limits for these boxes in the NEC and found that nearly every fixture is way over the limit. For example, the bathroom fixture has 13 "wires" (a mix of 12 and 14 gauge!) in it and each box is only a 4.5"x1.5" round box. The wire limit for this size box is 5.

The lights in use before I removed them were the type that are flush with the ceiling and thus didn't allow for much extra room. I am wondering if the light fixture size changes the number of allowed wires. For example, if the light fixture has a big ceiling mounted box like this one:

Does that change the allowable wire limit?

And, if not, is the only answer to get rid of the current boxes and put in much bigger ones? Is there a better way of addressing this issue?

Best Answer

Here is a Code language excerpt for your situation:

314.16(B) Box Fill Calculations. The volumes in paragraphs 314.16(B)(1) through (B)(5), as applicable, shall be added together. No allowance shall be required for small fittings such as locknuts and bushings.

(1) Conductor Fill. Each conductor that originates outside the box and terminates or is spliced within the box shall be counted once, and each conductor that passes through the box without splice or termination shall be counted once. Each loop or coil of unbroken conductor not less than twice the minimum length required for free conductors in 300.14 shall be counted twice. The conductor fill shall be calculated using Table 314.16(B). A conductor, no part of which leaves the box, shall not be counted.

Exception: An equipment grounding conductor or conductors or not over four fixture wires smaller than 14 AWG, or both, shall be permitted to be omitted from the calculations where they enter a box from a domed luminaire or similar canopy and terminate within that box.

So, the light fixture you have in your post would qualify as a domed luminaire and the wires from the fixture itself can be omitted from the calculation if there are only 4 or less. However, this does not add volume to the box calculation itself.

Unfortunately, junction box overfill is probably the number one violation of the Code.

Good luck and stay safe!

Related Solutions

Electrical – How to wire a light fixture with 3 white wires in box

If the old fixture worked, at least one of the white wires is hot.

The easiest way to check which is hot is to use a non-contact tester. If the fixture is already removed, leave the two wires bundled together with a wire nut over the end. Put a wire nut on the single white wire. Turn the breaker back on. Only one of those should register on tester. That is the hot side. The other should not register. That is the neutral.

Once you know which wire is hot, mark it with black tape or a permanent marker.

If the the fixture is still attached, you can do the same thing with the fixture hanging down. Once you know what is what, turn the breaker back off before wiring.

The black wire goes to the hot wire, the white to the neutral. The ground wire should be attached to a green or bare wire if there is one in the box, or to the box itself if it is metal. If not, just cap it.

Electrical – Ok to have junction box hidden behind recessed lighting

Accessible is a somewhat relative concept. You need to fully remove a recessed fixture from a ceiling to access the connections. This is a bit more difficult than pulling a switch to get at the wires, or even dropping a canopy style fixture, but it does meet the criteria of accessible.

But one of the main rationales for the rule seems to be to ensure a troubleshooter knows where all the connection are, that none are truly buried in the walls where they can't be found.

I don't know if the code has considered your solution, but it sounds like the box you are suggesting is buried, even though it is attached to the recessed fixture. In a sense, you are modifying the fixture in a way not contemplated by the manufacturer. But it might pass muster with some inspectors since it sounds like the junction would be accessible if you removed the can.

There is another way that might suit. The code now allows for certain in-wall splices that can be buried, such as these.

The old wire is inserted into one section of the device, clamped, and screwed in. A new wire is inserted into the other. The halves then snap together and the resultant splice can be buried in a ceiling or wall. If feasible, the completed clamp should be attached to a framing member, but I don't think the code requires it if the wire is left in an unaccessible area.

You could attach this splice to your old wire and run a short extension to your can.

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Best Answer

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Electrical – How to wire a light fixture with 3 white wires in box

Electrical – Ok to have junction box hidden behind recessed lighting

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