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Joined: Jul 2004
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The code really doesn't say much about how the cable gets secured in the box. It all comes down to the listing on the clamp or connector as far as I can tell and in a single plastic box you might not need to clamp it at all.
314.17(C) ex
Greg Fretwell
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Joined: Nov 2007
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Here are some FAQ's and what Carlon has to say about their nonmetallic zip boxes. Carlon FAQ's It would be interesting to know how many guys actually apply the required volume reduction of one conductor based on the largest size present in the box, for the built in quick "N" clamps in round ceiling and multigang boxes, when used. I think most EC's just assume that the manufacturer has already made the reduction in the volume, which they have not. In other than 1-gang boxes, having more than one NM cable per KO in boxes with the quick clamps seems to be a pretty common listing violation as well. Pretty small stuff as far as things go I guess, but still listing violations nonetheless.
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Joined: Mar 2007
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I have been told by an AHJ that the cables had to be the same or put 12-2 and 14-2 in different connectors in RI and Mass.
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Joined: Jul 2002
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Where cable needs to enter a panel, we use round TPS (not unlike "flex", it just has a thicker sheath).
The Gland used to effect that way through, into what might be an IP (Ingress Protection) rated enclosure, has a rating of IP68 (Dust-proof/Submersible).
I've never liked the idea of a clamping force on cables that are not round, not being circumferential.
There is potential for insulation migration, over a period of time
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Joined: Mar 2003
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KJay
So you feel a deduction should be made on Carlon boxes for supports in all but one gang which has none? The Carlon letter just states go to 314.16 which covers all deductions. You bought up something I;ve never thought of. I'v always felt the plastic taps in multigang boxes didn't count. I;d like to see what UL or others say about this. So you'd only count ones where romex was used? Or all. I;d say just where a Romex enters the box if at all.
Yoopersup
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Joined: Nov 2007
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Not to get to far off topic, but IMO that is correct, based on how the NM boxes are marked and from what I read in UL White book, which I included below.
Manufactures market these NM boxes as containing built in quick clamps and they are marked with the letter "N". According to UL, this indicates that they are clamps that are intended for use with NM cables.
On the other hand, if the box also includes a 1/2" KO and you used that with ENT connector instead, since the clamping mechanism is outside the box, the ENT connector would not have to be counted as box fill. The quick "N" clamps are also not used, so would not be counted either.
An interesting dilemma seems to exist for 1-gang NM old work boxes.
Since the cables can’t usually be secured within 12” of the box as with new work, these boxes typically contain quick “N” clamps or traditional "N" clamps with screws.
I’m not sure if it was the intention of UL or the NEC to allow these single gang old work boxes to be used with more than one cable in a single KO with clamps, but it seems that it should be okay based on the wording in the white book and NEC 314.17[C], exception.
If they meant this to apply only to 1-gang nail on boxes for new work, then I feel they should clarify this.
NONMETALLIC OUTLET BOXES (QCMZ)
GENERAL
This category covers nonmetallic flush device boxes, conduit bodies, conduit boxes, outlet boxes, special-purpose boxes, extension rings, covers, and cover plates for flush-mounted wiring devices, intended for installation in accordance with Article 314 of ANSI/NFPA 70, "National Electrical Code."
These products are also intended for installation and use in accordance with the following information.
CLAMPS
Boxes may or may not be provided with clamps. When clamps are provided,the carton is marked to indicate the type of wiring system or combination of systems for which they have been tested. The clamps are marked with the following letters or combinations thereof to indicate that they are suitable for use with nonmetallic sheathed cable "N’ or flexible tubing(loom) "T." Clamps suitable for nonmetallic sheathed cable are also suitable for multiconductor underground feeder and branch circuit cable where used in dry locations unless the box or smallest unit carton is marked "Nonmetallic Sheathed Cable Only." Clamps have been tested for securing only one cable per clamp, except multiple section clamps are considered suitable for securing one cable under each section of the clamp, each cable entering a separate knockout. All clamps are removed before the volume of the box is to be determined.
Boxes intended for use with nonmetallic sheathed cable or open wiring are suitable for use with cable or wire rated 90°C or less, unless marked for a higher rated wire in degrees centigrade.
SINGLE-GANG BOXA box nominally 2-1/4 by 4 in. or smaller is intended for one or more
nonmetallic sheathed cables to enter through a single or multiple stage
knockout opening
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