Box Fill

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physis

physis

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The last time I actually did a box fill calculation was at least a year ago. It was an existing bathroom remodle that needed a new circuit for 210.11(C)(3). I was able to come up through the garage with an EMT to the existing receptacle 4 sqr. We wanted to keep the sheet rock around the box intact and the fill was pretty close. So I checked the box fill.

I've talked to other electricians who say they haven't actually calculated box fill in "years". I basicly just use a big enough box.

I'm just curious if any of you guys are calculating the fill very often.
 
Re: Box Fill

Sam,

If this is leading into another thread like jap's residential 3-way, all I can offer is yes for box fill compliance. This prevents any fire insurance rejection claims defaulting to the contractor's liability. :D I occasionally do advisory work for HABITAT for HUMANITY and I suggest if any questions of wire fill is to look inside a listed box for the various allowable combinations and fire rating of the box.

rbj, Seattle
 
Re: Box Fill

Originally posted by physis:
I'm just curious if any of you guys are calculating the fill very often.
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Only for this forum and tests. :D

We always use large boxes, calculating the volume is not an issue.

New work is all 4"x4"x2.125" with rings, good for thirteen 12 AWGs, not including ring volume.

Old work is all 3 1/2" deeps, good for eight 12 AWGs.

Bob
 
Re: Box Fill

I'll do the calculations, on occasion. Probably 3 - 4 times a year.

A lot of my work is in existing wall surfaces, and avoiding wall patching that will be left for the homeowner gets "good favor" points when it is the homeowner that writes the check. This results in picking boxes that are just the right size.

Since this is job specific, how many times I check my assumption depends on job politics as well.
 
Re: Box Fill

Bob,

I have a suspicion that your seat-of-the-pants sense of box size is what I would experience as dead reckoning.
 
Re: Box Fill

Had one couple of weeks ago, a 4" round bell box. Came out with 3 conductors too many. Ever try to find an extension for this? All my suppliers had the square extension but not the round. :(
 
Re: Box Fill

Usually we use deep 4 square boxes for a single receptacle so this isn't usually an issue and we have plenty of room.
However, in a recent Loew's I did myself [mostly], there was a box feeding the main office area. I DID use a calculation on that. There were six circuits involved and I figured that if most of the conductors were pulled straight through, which was quite possible if people would think, there would be only two splices required. One neutral had to be divided [count 3] and of course the ground [count 1].
But the guys pulling the wires seemed to operating at the Romex or MC level and they seem to love using up wire nuts. So I have a hunch that there's a lot more cable fill in that box than is lecit. :(
~Peter
 
Re: Box Fill

a 4" round bell box. Came out with 3 conductors too many. Ever try to find an extension for this?
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I have a few in the van. Only cause I don't use them often. :)

So I have a hunch that there's a lot more cable fill in that box than is lecit.
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Yeah, ! , That's when I count it.

[ November 06, 2004, 10:18 PM: Message edited by: physis ]
 
Re: Box Fill

Not to long ago i had a helper that had 4 12/2`s in a WP receptacle,cut in box. When I explained box fill he answered why are there 4 openings in a box if they cant be used.....DUHHHHH
 
Re: Box Fill

Do you suppose this same person figures if there's still check blanks in the book, there must be money? :D
 
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