cable trays

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guschash

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When using cable trays in a residential house do we have to do a ampacity adjustment? My thinking is we should, but I was just in a new home and they used a cable tray from the panel and ran it down the middle of the basement and branch off where needed. Simple but do we adjust for ampacity?

gus
 
If the trays and cables are installed per the proper Sections of Art 392.9, then ampacities are determined by Section 392.11. It can be faily complex, but unless there are more than 3 conductors per cable, not cable tray, then the derating factors of 310.15(B)(2)(a) won't apply. However, there are several other "adjustments," that are too numerous to summarize here.
 
I have not installed anything yet. This residential plastic cable tray with NM in it. Must be 10 or 15 or more in this tray in a basement of a new house.

gus
 
My original comment stands. Since NM is acceptable in cable trays [Table 392.3A)]. If the cables are installed per 392.9 (and they MUST be), the ampacities are determined by 392.11.
 
rbalex said:
My original comment stands. Since NM is acceptable in cable trays [Table 392.3A)]. If the cables are installed per 392.9 (and they MUST be), the ampacities are determined by 392.11.
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(I wasn't disagreeing with you (I know better :D) , I was simply curious as to the possible plan to use TC in a residential application.)
 
augie47 said:
(I wasn't disagreeing with you (I know better :D) , I was simply curious as to the possible plan to use TC in a residential application.)
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I was actually responding to guschash's Post #5, but thanks for the vote of confidence. ;) (I had assumed NM) Unfortunately, TC has a restriction on it [336.12(2)], that shouldn't be there in my opinion. It is obiously a far superior construction than NM, including several flame tests not applied to NM, but it still can't be run outside the tray (or a raceway) in a residential application.
 
Arlington makes these trays called " Cableway " . I see them advertised in "EC&M". It shows a residential application with many NM it. Do these NM cables need to be derated? I don't know what 336.12(2) has to do with it.

gus
 
In reading Article 392.80 in the 2011 workbook I see that there must be ampacity adjustment. Thanks for the replies.

gus
 
guschash said:
Arlington makes these trays called " Cableway " . I see them advertised in "EC&M". It shows a residential application with many NM it. Do these NM cables need to be derated? I don't know what 336.12(2) has to do with it.

gus
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Gus was apparently thinking your installation might use Type TC cable. I was responding to him by saying Section 336.12(2) essentially prohibits using TC for your residential application as described.

The Arlington Cableway is a solid bottom tray; therefore, the maximum permitted fill is defined in 392.9(C). Since NM is by definition,"multiconductor", the ampacities are then determined by 334.80 and 392.11(A)(1) as possibly adjusted by 310.15(A)(2). Remember to consider the ambient.

All that is to say you still have a lot of computing to do, but you don't have to consider 310.15(B)(2)(a) because cable tray is not a raceway. That it is about as detailed as I can get wihout actually designing it for an appropriate fee . (This is NOT a solicitation:D)
 
I already owe him more than I make for all that I have learned from his "free" posts.
The info on this Forum is often priceless.
 
rbalex said:
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All that is to say you still have a lot of computing to do, but you don't have to consider 310.15(B)(2)(a) because cable tray is not a raceway. That it is about as detailed as I can get wihout actually designing it for an appropriate fee . (This is NOT a solicitation:D)
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Bob,
What about the portion of that section that I have shown in bold?
(2) 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 installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.
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rbalex said:
Don,
I believe 392.11(A)(1) exempts the cables from that requirement; otherwise is a useless statement.
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Bob,
I would agree that the specific rule would over rule the general rule, but was really looking at your choice of words. You said that the derating rule would not apply because it is not in a raceway. Where I am going with this is, that the product in question in this thread is not listed as a cable tray and the rule in 392.11 does not apply. It is listed under "Conduit and Cable Hardware" (DWMU)
It is also not a raceway, but, in my opinion 310.15(B) applies.
 
don_resqcapt19 said:
Bob,
I would agree that the specific rule would over rule the general rule, but was really looking at your choice of words. You said that the derating rule would not apply because it is not in a raceway. Where I am going with this is, that the product in question in this thread is not listed as a cable tray and the rule in 392.11 does not apply. It is listed under "Conduit and Cable Hardware" (DWMU)
It is also not a raceway, but, in my opinion 310.15(B) applies.
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Don,

I believe I see your point and appreciate you keeping me honest. I should have simply left it that 392.11(A)(1) eliminates consideration of 310.15(B)(2)(a) without reference to it being a raceway or not.

But I’m still not quite sure how far apart we are on this.

If you are saying that 310.15(B) still generally applies, but agree that 310.15(B)(2)(a) specifically doesn’t, then we’re in complete agreement.

If you believe 310.15(B)(2)(a) still applies and 392.11(A)(1) doesn’t because the “Cableway” is not listed as a cable tray, we still have something to discuss.

Non-metallic cable trays (UL Cat Code CYOV) aren’t listed for their affect on ampacity of conductors installed in them. They are listed as support systems “… intended to be installed in accordance with NEMA VE 2, or as recommended by the manufacturer.”

Category Code DWMU also recognizes the purpose is for “Hardware for the Support of Conduit, Tubing, and Cable.” Where appropriate, the listing includes structural loading restrictions.

The root definition (392.2) is, “A unit or assembly of units or sections and associated fittings forming a structural system used to securely fasten or support cables and raceways.” Note that nowhere in Art 392 is the cable tray itself required to be listed – for anything. Since this particular application is residential, even OSHA’s long arm doesn’t reach that far.

As far as the use of the Arlington Cableway, “If it quacks like a duck…” I still say 392.9(C) and 392.11(A)(1) apply and 310.15(B)(2)(a) doesn’t.
 
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Bob,
I don't think we will agree on this one. Even bundles of NM in open air have to be derated if bundled for more than 24". The issue is heat and I can't see how less heat would be created in the cable support system than in bundled cables in open air. Now if you would install the NM in the "Cableway" in a manner that would maintain spacing between the conductors then I would say you would not have to derate.
 
If the cables are installed per the appropriate part of 392.9, I don't believe they should be considered "bundled." Otherwise, there is no practical purpose for any part of 392.11 for any cable tray installation. We may as well consider any cable tray installation a "bundle."
 
Bob,
How do you comply with 392.9(A)(2) when the Cableway has a width of less than 6"? I guess we could extrapolate a bit. The volume permitted in square inches is ~90% of the tray width. The Cableway product is 2" wide so we should be able to put 1.8 square inches of cable in the tray. Southwire's 12-2NM is 0.410" wide and 0.179" high. A single cable would have a area of 0.073 square inches. That would permit us to put 24 12-2 cables in the tray. That would be 4 wide and six deep in the Cableway. I would consider that to be "installed without maintaining spacing".

I am not convinced that Article 392 was ever envisioned to be used for applications like this. It wasn't that many code cycles ago that the use of cable tray was limited to industrial applications. Has there ever been any testing with this number of NM cables installed in this manner?


I see that 334.80, specifically says that the ampacity of NM installed in cable trays is per 392.11, so you are correct.
 
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