What's the largest box I can use for a sconce light? Can a 4" square box with round mud ring be used?

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mnoone

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Hello! I am planning out the electrical work for my upcoming bathroom remodel.

I have one junction box that I think is going to be busy. It looks like it is going to have:

2x 12/2
2x 14/2 (this could be 1x if needs be)
2x 14/3
1 sconce light (with 18 AWG wiring, so I think it does not count into box fill)

I think this gives me: 4 conductors for the 12/2, 4 conductors for the 14/2, 6 conductors for the 14/3, and 1 conductor for the ground. So 15 total assuming I'm using clamps outside the box. Or 13 if I get rid of one of the 14/2s (which I can do). Hopefully I did that calculation right?

I would like to use a metal, new construction box. My options are... limited. 2020 NEC table 314.16(a) shows 13 12 AWGs allowed in a 4x2 1/8 box. But how do I connect a sconce to a square box? I looked at round mud rings (like Hubbell 757) but the spacing between the two threaded holes on it does not match the spacing on a normal round or octagonal junction box. Is that still an appropriate way of hooking up a sconce? I know sconce lights often have multiple diameters of hole spacings they support so I'm guessing this is OK - but want to double check.

Is this my best path forward, or can you suggest another alternative? I would really like to avoid adding more junction boxes (for purely aesthetics reasons).

Thank you for your assistance!
 
mnoone said:
Hello! I am planning out the electrical work for my upcoming bathroom remodel.

I have one junction box that I think is going to be busy. It looks like it is going to have:

2x 12/2
2x 14/2 (this could be 1x if needs be)
2x 14/3
1 sconce light (with 18 AWG wiring, so I think it does not count into box fill)

I think this gives me: 4 conductors for the 12/2, 4 conductors for the 14/2, 6 conductors for the 14/3, and 1 conductor for the ground. So 15 total assuming I'm using clamps outside the box. Or 13 if I get rid of one of the 14/2s (which I can do). Hopefully I did that calculation right?

I would like to use a metal, new construction box. My options are... limited. 2020 NEC table 314.16(a) shows 13 12 AWGs allowed in a 4x2 1/8 box. But how do I connect a sconce to a square box? I looked at round mud rings (like Hubbell 757) but the spacing between the two threaded holes on it does not match the spacing on a normal round or octagonal junction box. Is that still an appropriate way of hooking up a sconce? I know sconce lights often have multiple diameters of hole spacings they support so I'm guessing this is OK - but want to double check.

Is this my best path forward, or can you suggest another alternative? I would really like to avoid adding more junction boxes (for purely aesthetics reasons).

Thank you for your assistance!
Click to expand...
2 x 12/2 = 4 x #12AWG = 4 * 2.25cu = 9cu
2 x 14/2 = 4 x #14AWG = 4 * 2.00cu = 8cu
2 x 14/3 = 6 x #14AWG = 6 * 2.00cu = 12cu
-------------------------------------------------
Total Cubic Inches = 29cu

Per 314.16(B)(1) Exception, "...not over four fixture wires smaller than #14 AWG ...shall be permitted to be omitted from the calculations where they enter a box rom a domed luminaire or similar canopy and terminate within that box."

A standard 4" x 4" SQ box is 21cu, but the cu must be stamped on it.
The ring, per Hubbel's website adds 6.5cu, giving you a total of 27.5cu, leaving you short by 1.5cu.
Solution is a deeper ring or a deeper box... or find a way to have less conductors.

You do not require an Octagonal 8B box for fixtures, despite what some people may say.
The holes on an 8B box works for fixtures because you typically install a bracket, which offsets to an additional set(s) of threaded screw holes, one set of which will match the spacing on a square to round ring.

Square to round rings work for most fixtures in my experience, are fine for fixtures up to 50lbs, and will still accept a bracket.
However, it might be worth your while to check the spacing on your fixture.
 
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This is the funniest thing I've seen today :ROFLMAO::ROFLMAO:
Can I use this to install a ceiling fa... NO. But what if... NO. Not even if I... NO.
 
I imagine there are equipment grounding conductors so those need to be taken into consideration in addition to the 29 cuin.
The amount added depends on which Code cycle is in place.

Bottom line, you might be better off to have a j box and limit the number of NMs to the sconch light box.
 
augie47 said:
I imagine there are equipment grounding conductors so those need to be taken into consideration in addition to the 29 cuin.
The amount added depends on which Code cycle is in place.

Bottom line, you might be better off to have a j box and limit the number of NMs to the sconch light box.
Click to expand...
Good catch. Did that a little fast. Missed the EGC.
Have I missed something in 2020 regarding EGC's for box fill?
 
augie47 said:
I imagine there are equipment grounding conductors so those need to be taken into consideration in addition to the 29 cuin.
The amount added depends on which Code cycle is in place.

Bottom line, you might be better off to have a j box and limit the number of NMs to the sconch light box.
Click to expand...
Looks like I did in 2020. I was unaware of this change. Aww man, I'm gonna miss counting all the EGCs as one volume, lol.

So it looks like...

First 4 EGCS counted as one at largest size:
2.25cu

Last 2 EGCS counted at 1/4" allowance at largest size:
2 x 2.25 x 1/4" = 1.125cu

Total EGC volume = 3.375cu

New Final = 32.375cu
 
Jerramundi said:
Looks like I did in 2020. I was unaware of this change. Aww man, I'm gonna miss counting all the EGCs as one volume, lol.

So it looks like...

First 4 EGCS counted as one at largest size:
2.25cu

Last 2 EGCS counted at 1/4" allowance at largest size:
2 x 2.25 x 1/4" = 1.125cu

Total EGC volume = 3.375cu

New Final = 32.375cu
Click to expand...
Thanks for taking the time to run the numbers. One question - you used 21 cu which I think is a 4"x1 1/2" box. Any reason I can't use a 4"X x 2 1/8" box? (30.3cu)

I had not realized the detail about counting last 2 EGCS as 1/4 largest. That's interesting. But with the deeper box and the mud ring I think I am OK? (6.5 + 30.3 = 36.8 cu).

Thank you!
 
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