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NM Trough? #88409 06/01/04 06:22 PM
Joined: Feb 2003
Posts: 138
WebSparky Offline OP
Hi Guys,

Here is an install in a new house I inspected last week. This is the first time I have seen this method for NM installs. The "rings" have a snap-around 3-sided cover to close the sides and bottom.

[Linked Image from]

[Linked Image from]

Let's suppose that the securing is not an issue and see if:
(1)the install will comply with the derating and
(2)with the fill allowance of 40% specified by the manufacturer.

310.15(B)(2)(a) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a).

(1). The install has six 12/3WG NM cables, six 12/2WG NM cables and one 8/3WG NM cable.
Current carrying conductors: (12/2)= 6, (12/3)= 12 and (8/3)= 2, for a total of 20 current carrying conductors.
According to the Table, the derating is 50%. The 12AWG would be reduced to 15A and the 8AWG would be reduced to 22.5A. The breakers installed are 20A and 40A respectively.

(2.) Let's guess the size of the 12/2NM is 3/8", (.375 x 6) = 2.25 sq."
Let's guess the size of the 12/3NM is 1/2", (.5 x 6) = 3.00 sq."
Let's guess the size of the 8/3NM is 3/4" = .75"
That would give us a total of (2.25 + 3.00 + .75) 6.00 sq." fill.

The product has a cross section of 7.25 sq.". When we calculate 40%, we have a result of 2.90 sq.".

Based on the above calculations, (if you agree they are acurate) would you agree that the install does not satisfy these code requirements?

Thanks for your consideration.

2017 / 2014 NEC & Related Books and Study Guides
Re: NM Trough? #88410 06/01/04 07:46 PM
Joined: Feb 2003
Posts: 138
WebSparky Offline OP
Hold on.....

I screwed-up the calcs!

Re: NM Trough? #88411 06/01/04 08:27 PM
Joined: May 2004
Posts: 186
aland Offline
accuracy and guessing do not fit well together

Re: NM Trough? #88412 06/01/04 08:39 PM
Joined: Jan 2004
Posts: 1,507
George Little Offline
WebSparky- that product was invented by a contractor here in Michigan and it has a UL listing to do just what you show. There is a spec sheet that tells you how many NM cables are permitted and the derating usually is not an issue. If you can't get access to that spec sheet let me know and I'll put you in touch with the gentleman who is responsible for getting it listed. It's actually a pretty good product.

George Little
Re: NM Trough? #88413 06/01/04 09:26 PM
Joined: Jun 2003
Posts: 681
PCBelarge Offline
How does the listing of this product get around the requirement for cables run perpendicular to the unfinished basement beams?


Pierre Belarge
Re: NM Trough? #88414 06/01/04 10:04 PM
Joined: Apr 2002
Posts: 558
caselec Offline
Why are these brakets UL listed? Normally staples, straps, bridle rings, etc. are not UL listed. If you look at a Caddy or B-Line catalog I don’t think your going to find many items UL listed. Do you happen to know the manufacture and UL number?

Since these brackets are not a raceway I don’t see why they would be limited to 40% fill. I definitely feel that the ampacity might need to be adjusted according to Table 310.15(B)(2)(a) but from the pictures of this installation there seems to be a fair amount of air space between the conductors I don’t see much of a problem.

As I mentioned on the MH site my real problem with this installation would be that it doesn’t comply with 334.15(C).


Curt Swartz
Re: NM Trough? #88415 06/02/04 02:31 AM
Joined: May 2004
Posts: 186
aland Offline
love to join in on some of these guys, but is there a place on the webb where I can get to understandig what code 334.15 states?
One problem I have with the device shown is the distance between them, looks about 28 - 30 inches, thats quite away for an unsupported loop in a cable. Get a whole bunch of cables and your adding weight onto the point where cables cross the hangers, add a bit of heat and over time you could have a potential fault develope.
Great site this with good topics I love it.
Only thing is it gets a bit addictive, should be out now earning. Catch you later guys!

Re: NM Trough? #88416 06/02/04 07:33 AM
Joined: Jan 2004
Posts: 1,507
George Little Offline
For those of you who are worried about 334.15(C), you need to see the complete product as discribed by WebSparky in his initial post. There is a 3 sided box cover that goes on those "rings" and the finished product resembles a trough when it is finished. If I knew how to post a graphic on this site I'd be able to illistrate my point and post the specs on this product.

George Little
Re: NM Trough? #88417 06/02/04 12:35 PM
Joined: Jun 2001
Posts: 642
nesparky Offline
Does the manufacturer have a web site?
you can send pictures to bill and he will post them for you.

Re: NM Trough? #88418 06/02/04 01:38 PM
Joined: Feb 2002
Posts: 375
George Offline
While it might appear that derating is required, I don't think so.

There are other wire combinations that after derating produce more heat than this wire combination before derating.

The total breaker amperage at 220v of these wires appears to be over 200amps. So the current is limited by the mains not by the actual breakers.

Load diversity/actual usage would place the actual heat production at a fraction of what is allowed.

Too much attention is paid to derating in a residence.

[This message has been edited by George (edited 06-02-2004).]

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