Plastic Old work box fill.

E

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
Carlon BH641R says 14.5 cu " inside7/14s, 6/12s and 5/10s box has internal clamps

So, my question is the 14.5 cu inches has Carlon already deducted the allowance for the clamps, and you have the entire 14.5 cubic inches to use? That is what I assume. Or do you have to deduct an allowance for internal clamps like you do with a metal box that has internal clamps.
 
What do the fill calculations for each of those wire sizes and quantities?

Simple check: what is 14.5/7, /6, and /5, respectively?
 
Eddie702 said:
Carlon BH641R says 14.5 cu " inside7/14s, 6/12s and 5/10s box has internal clamps
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#14=2 cubic inches, 7*2=14 cu in
#12=2¼ cubic inches, 6*2.25=13.5 cu in
#10=2½ cubic inches, 5*2.5=12.5 cu in

There has been much debate about this over the years. I thin that Dennis once provided some documentation from Carlon that said you had to count the internal clamps which is dumb when the number of conductors is stamped into the box.
 
hbiss said:
Clamps count just like with metal boxes. The number of conductors stamped on the box is with no clamps- you are supposed to know to do the math from there. (y)

-Hal
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So if they're going to provide this information why wouldn't they stamp the actual fill number into the box?
 
Eddie702 said:
Carlon BH641R says 14.5 cu " inside7/14s, 6/12s and 5/10s box has internal clamps

So, my question is the 14.5 cu inches has Carlon already deducted the allowance for the clamps, and you have the entire 14.5 cubic inches to use? That is what I assume. Or do you have to deduct an allowance for internal clamps like you do with a metal box that has internal clamps.
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I would think that 14.5 cu in is what you have to work with.

Do the math for whatever you’re putting in there.
 
To me the issue is with a metal box that has clamps you can use them and count them as part of the fill or remove them and use plastic snap in connectors or metal Romex connectors and not have to count them as part of the fill. But with plastic you have no choice the clamps are part of the box.

So the question remains. Does the 14.5 cubic inches mean the clamps have already been included or do you have to deduct for them? I downloaded the Carlon catalog and it says nothing about this.
 
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This is very old from Carlon but I don't think that the results are any different. My opinion is that they did not understand the type of box in question. When you look up a B520A there is no way to remove the clamps for testing as suggested in the answer.

Q. All your blue boxes come stamped with a wire volume and corresponding conductor count. Do the volume and/or wire count account for the integral clamps that are present in many of your boxes? For instance, your B520A-UPC ceiling box has a 20 cubic inch volume and
therefore can receive ten (10) #14 gauge wires per the NEC. However, it also has six integral clamps. Per the Article 370-16(b)(2), where one or
more internal cable clamps, whether factory or field supplied, are present in the box, a single volume allowance in accordance with Table 370-16(b)
shall be made based on the largest conductor present in the box. Therefore, does the installer need to take into account a volume reduction? Is the true available volume in the example above really 18 cu.in. assuming the use of #14 gauge wire? Other boxes, such as some of your single gang models, have knock-outs in lieu of integral clamps; so, the actual wire count is not an issue.

A. The volume inside an outlet box does not include any deductions for integral clamps. The clamps are removed from the box when the volume is determined by UL. Therefore a single deduction in the NEC is required for the space the clamps take up inside the box. A B520A is 18 cubic inches after the clamp deduction for #14 wire. This procedure was determined by IAEI and UL. Not everybody agrees to this. The 2002 NEC (314.16(B)(2)) still has the deduction requirement. Keep an eye on the 2005 NEC because it may be changed
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Originally all NM boxes used clamps that were screwed in similar to metal boxes. Anytime that Carlon letter comes up I feel its in error for the current box design where the clamps in most boxes are molded into the box so don't take any "space". As Infinity said there is no way to remove the clamps without destroying the box.
 
curt swartz said:
Originally all NM boxes used clamps that were screwed in similar to metal boxes. Anytime that Carlon letter comes up I feel its in error for the current box design where the clamps in most boxes are molded into the box so don't take any "space". As Infinity said there is no way to remove the clamps without destroying the box.
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After looking at the actual Carlon box in question I agree with Curt. I originally was under the impression that this box had actual clamps from what the OP was saying, but what is there are basically just knock-outs that you stick the cable through like most plastic boxes today. They are not clamps nor are they removeable, so they have no effect on the volume of the box. However, the user should figure box fill the usual way, not go by what is stamped on the box.

-Hal
 
wwhitney said:
Integral clamps are not the same thing as internal clamps. The integral clamps on these modern plastic boxes are not internal.
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They aren't even clamps as far as I'm concerned. They just close the hole up when it isn't being used. Romex staples or other supports within 6" of the box are what is supposed to secure the cables. Don't know what happens when the cable is fished.

-Hal
 
wwhitney said:
Integral clamps that do not take up any noticeable space inside the box.


Agreed, instead it's part of the box itself. Any internal volume change when you stick a flat cable through there is negligible.

Cheers, Wayne
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I don't agree if that were true the Romex clamps in a metal box take less room than the plastic ones. In fact I think the clamps in the metal box take no space at all.
 
Eddie702 said:
I don't agree if that were true the Romex clamps in a metal box take less room than the plastic ones. In fact I think the clamps in the metal box take no space at all.
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Not sure how you can say that. The internal clamps in metal boxes definitely take space. I seldom use metal boxes with internal clamps but when I do I always remove and unused clamps.
 
hbiss said:
They aren't even clamps as far as I'm concerned. They just close the hole up when it isn't being used. Romex staples or other supports within 6" of the box are what is supposed to secure the cables. Don't know what happens when the cable is fished.

-Hal
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314.17(B)(2) requires the wiring method to be secured to the box, exception being one gang non metallic boxes if the first supporting means is within 8 inches of the entry into the box. So they are required to be a securing means which many will call a clamp. Years ago we used to fail inspections if we had "broken clamps" and the section I mentioned (or whatever had same info if it has moved)is what was cited. This was easy to break those if you didn't use a little care during installation, particularly with the Carlon boxes. Still is if installing in cold weather, I generally don't use plastic boxes bigger than two gang for most situations and even two gang I avoid plastic boxes quite often - drywallers find ways to twist and distort them making more difficulty at trim out. Fiberglass boxes are my preference other than for one gang or round boxes most the time.
 
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