I'm installing a flood lamp on my outdoor garage. So, I went to take look at the junction box, and to my surprise, it appears oddly filled:

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Filled to the point where I almost feel as though it's too filled.

The junction box is 4x4x2 1/2. There's at least from what I can count 4 different circuits running out there:

1) washer + misc outlets in garage

2) dryer

3) garage lights (outdoor)

4) garage lights indoor + garage opener

The house was built in the 1980's - I live in the Pacific Northwest (specifically, Washington State).

I do have a 5x5 that I purchased that I could replace it with, but I wasn't sure if I should "extend it" or just "replace it" entirely, which I guess would be the second half of my question.

I'm adding the flood lamp to the same circuit as the rest of the outdoor garage lights.


2 Answers 2


The rules for box fill are contained in NEC 314.16(B). Generally, if you are using 14 AWG wire, you need 2 inches of space for

  • each power carrying (hot and neutral) wire
  • all ground wires counted as one
  • internal cable clamps (usually in metal boxes) counted as one (external clamps and built-in clamps on a plastic box don't count)
  • hickeys or other light fitting devices count as one
  • each strap containing a device (a duplex outlet or double switch count as one)

If the wire is 12 AWG, all figures are increased to 2.25.

If you do the math and your box has too many wires, including any you need to add, you need either a bigger box or a second box.

If appearance isn't an issue, you can get box extenders that protrude from the front and add inches.

Depending on how the wires feed into the box, you maybe able to add another box a few inches to one side or the other, removing a few circuits from the original box, terminating them in the new, and just connecting the live feed between the old and new.


A 4" × 2 1/8" square box, has a volume of 30.3 cu. in.. If all the wires in that box are 14 AWG, you can fit 14 current carrying conductors plus whatever grounding conductors there are.

You mentioned a dryer circuit, which makes me think that at least some of the wires are 10 AWG. Those wires require 2.5 cu. in. per wire, rather than 2.0 cu. in. required by #14. It also means that the grounding conductors have to use the 2.5 cu. in. value as well.

This answer provides more detail on how to calculate the size of the required box.

A quick count, and it looks to me like there's more than that in the box. Assuming each twist-on wire connector connects at least two wires. I've counted at least 8 connectors, which would be 16 wires, and 32 cu. in. of required space.

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The danger of having too many wires, is that there's not enough space to dissipate heat to. As current flows through wires, it generates heat. If the heat can't dissipate, you can end up melting insulation and causing a short-circuit, or possibly starting a fire.

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