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.





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.




(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.

Hold on.....

I screwed-up the sq.in. calcs!

accuracy and guessing do not fit well together

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.

How does the listing of this product get around the requirement for cables run perpendicular to the unfinished basement beams?

Pierre

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

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!

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
Does the manufacturer have a web site?
you can send pictures to bill and he will post them for you.

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).]

Click Here for more info.

So, up t0 30 12-2 type NM cables can be bundled together with no derating required? That just don't sound right!

Not much info available on the web. The product is made by "Speedway Electrical Products". A google search gives _one_ hit; a news blurb saying that Tom Lhota invented the stuff and is selling it direct.

The UL file doesn't say very much.

Ahh, heck with it. UBB doesn't seem to want to parce the long url. Go to www.ul.com and look up file E190378


I presume that if UL tested each of the cables at rated ampacity, at the 40% fill, and that there was no overheating, then derating is not needed...but I see nothing in the guide information that suggests this sort of testing.

-Jon


[This message has been edited by winnie (edited 06-03-2004).]

George and Jon,

Thanks for your help!

My concern is the amount of cables listed as to be acceptable! There sure seems that there needs to be derating because of bundling. At least, I think it is bundling!

If this is not considered bundling, what is??

Where do we "draw the line"?

WebSparky ---

Derating for bundling is very poorly done in the code. It treats conduit in free air the same as conduit in foam insulation and it treats small conduit the same as large conduit.

If a manufacturer of conduit wanted to, he could get UL approval for more accurate derating. This manufacturer appears to have done so. He was smart enough to make his design incompatable with other conduit designs.

Thanks George!

I think I'll call him from the office on Monday to see if he can fax me the UL Listing information.

Thanks for the help!

Dave Nix

George is right. Derating for residential is overblown.
If there is tight packed cables run through tight packed insulation You might just heat up your cables somewhat, but up to 90 degrees centigrade? I doubt it. First we should be looking at the loading on the cable runs in a dwelling. Most are underloaded from the branch circuit rating. Where you are more likely to find wires or cables that should need de rating is in the commercial or industrial setting. I'm sure most of us have run across those way to warm or hot runs of conduit that somebody packed up with too many wires. Especially true where lay in flourescent lights keep getting added to existing circuits. But truthfully have any of you inspectors or fire marshall's out there ever seen a fire start because someone pulled more than 3 runs of romex thru a series of drilled holes? Be honest about your answers now.

What is the name of this product and where can I buy it. Can't seem to find anything on the web. If it is no longer available is there another product that performs a similar function?

thanks