Code violation for troughs

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danmc9

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I installed three 200 amp panels with 42 circuits each. I have a 6"x6" trough that is 12 feet long. The local electrical inspector says I can only have 41 circuits in this trough. I will have about 120 wires. I checked the code book and found wireway codes, but he is looking at the cable tray codes. I was not planning to derate these wires. Most are 20 amp circuits for lighting and power. It is a day spa.
Thanks....Dan
 
You might want to stick with his assesment.... In both 366 and 376 which ever applies, you would need to derate at 30 CCC's. It sounds as if 376.22 is where you need to look.

From commentary:
The main requirement of this section is that the total of the cross-sectional areas of all conductors must not exceed 20 percent of the interior cross-sectional area of the wireway. If the quantity of conductors does not exceed 30, the adjustment factors of 310.15(B)(2) do not apply.
Click to expand...

I should also add that it applies to the cross-sectional area - not the WHOLE gutter - just that portion of the gutter where the count exceeds 30 CCC's....

I say this because I often take conductors verticaly through horizontal gutters using as a pull box... And stay below 30 CCC's in each area of the gutter. Sure you could still use as a wireway with limited use in that way, but you need to remain below 30 to escape derating and stay below 20% fill....
 
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I'd like to see how the inspector came up with a max. number of circuits.

Trough cable fill is covered n 366/376/378.22 and applys to the number of conductors, not circuits.

If you have 120 wires, you need to derate.
 
480sparky said:
Trough cable fill is covered n 366/376/378.22 and applys to the number of conductors, not circuits.
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Good catch on 378 - I live in a world without plastic.... 378 has much less leway on derating, and appears to not give you that 'no derating till after 30'.....
 
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376.22

376.22

So if danmc9 has to derate his conductors using table 310.15(B)(2)(a) according to 376.22 does he need to derate all 120 ccc at 35% or is it just the ccc over 30?
 
e57 said:
You might want to stick with his assesment.... In both 366 and 376 which ever applies, you would need to derate at 30 CCC's. It sounds as if 376.22 is where you need to look.

From commentary:


I should also add that it applies to the cross-sectional area - not the WHOLE gutter - just that portion of the gutter where the count exceeds 30 CCC's....

I say this because I often take conductors verticaly through horizontal gutters using as a pull box... And stay below 30 CCC's in each area of the gutter. Sure you could still use as a wireway with limited use in that way, but you need to remain below 30 to escape derating and stay below 20% fill....
Click to expand...
You could put a divider in the trough with chase-nipples installed in the divider. Now you can have 30 CCC's on each side of the divider...
 
480sparky said:
I'd like to see how the inspector came up with a max. number of circuits.

Trough cable fill is covered n 366/376/378.22 and applys to the number of conductors, not circuits.

If you have 120 wires, you need to derate.
Click to expand...


Maybe not...
"376.22 Number of Conductors.
The sum of the crosssectional areas of all contained conductors AT ANY CROSS SECTION OF A WIREWAY"



Qoute from Mike Holt -
"Conductor ampacity adjustment only applies when more than 30 current-carrying conductors are installed in any cross-sectional area of a metal wireway"

The way I read all of this is, if the conductors are not all traversing the length of the wireway, one would only apply the derating rule to the number of conductors per any portion of cross section they occupy.
 
captaincrab55 said:
You could put a divider in the trough with chase-nipples installed in the divider. Now you can have 30 CCC's on each side of the divider...
Click to expand...

I don't think that would fly - it is still a wireway as a whole unless the divider is listed for the purpose.... To create two wireways... (FYI - the code does not seem to require listing on metal wireways...)

Or you could try this.... I have with limited success. :roll: "Is that a wireway?" - "No - it is a 6"X6"X144" junction/pull box!" :grin:
 
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somebody check me

somebody check me

I was trying to see how many #12 THHN wires you could put in 20% of a 6"x6" trough.

6x6=36 x 20% = 7.2 sq. in.
7.2 / .0133 (sq. in. of #12 THHN per Chapter 9 Table 5) = 541.

541 #12 conductors are allowed? Man that seems like a lot.
 
Pierre C Belarge said:
Here is an interesting fact about wireways I was not aware of.


Cooper Bline wireway installation procedures -

http://cooperbline.com/CBCD/Design%20Center/Enclosures/Wireway%20Selection%20and%20Sizing.pdf


Take a look at steps 6 & 7 on page 3.
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What - that they are also under the pull-box rules for bending wire? - The '02 NEC (not sure if it was removed later...) at least also requires it be sized for largest conduit entry when those conductors are larger that #4 from that entry. See 376.23(B) So it is wize to choose small conduit or nipples when using #4 or larger.... Not bring them in through a 3"... Bring them in via a 1" or smallest nipple sized for the conductor....
 
hardworkingstiff said:
I was trying to see how many #12 THHN wires you could put in 20% of a 6"x6" trough.

6x6=36 x 20% = 7.2 sq. in.
7.2 / .0133 (sq. in. of #12 THHN per Chapter 9 Table 5) = 541.

541 #12 conductors are allowed? Man that seems like a lot.
Click to expand...

Yes - it does, but you would not be able to due to derating - you would end up with a LOT LESS (30 current carrying), or much larger wire.... When derating starts to apply in gutters you are already at 40% once you have 31, at 41, you are then into the 35% range. Meaning those 20a circuits should now be #6!!! A mighty big gutter to have 57" as 20% = 1127" as an area.... Thats a 3'x3' gutter!!! (if all 541 were CCC's...)
 
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e57 said:
I don't think that would fly - it is still a wireway as a whole unless the divider is listed for the purpose.... To create two wireways... (FYI - the code does not seem to require listing on metal wireways...)

Or you could try this.... I have with limited success. :roll: "Is that a wireway?" - "No - it is a 6"X6"X144" junction/pull box!" :grin:
Click to expand...
Good question about the divider being listed.. I never had a problem with custom built trough.. BTW, Wiremold 4000 & up does have dividers & hardware avaiable...
 
This subject came up in class just the other night and a note of the exception in 310.15(a)(2) was given for a possible "way out" if you will. If the majority of your runs are 100' or more, and the trough is less than 10' you should be ok for not having to derate the ccc's.....at least that's how I understood it. If I am way off, could someone shed some light on this for me?
 
boyle78 said:
~and the trough is less than 10' you should be ok for not having to derate the ccc's.....at least that's how I understood it. If I am way off, could someone shed some light on this for me?
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Sure.... You're off by about 8' (96") - the code you're refering to is for sections no longer than 24".... And it matters not how long they are. This counts for any portion or area of raceway or cable method where derating is applied - the 24" rule just means you don't have to think about it untill after 24". You could have 23 7/8" then seperate them to avoid derating, and another 23 7/8".

(MY bad - see later post....)
 
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e57 said:
Sure.... You're off by about 8' (96") - the note you're refering to is for sections no longer than 24"....
Click to expand...

:-?

310.15(A)(2) Selection of Ampacity Where more than one calculated
or tabulated ampacity could apply for a given circuit length,
the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent
portions of a circuit, the higher ampacity shall be permitted
to be used beyond the point of transition, a distance equal
to 3.0 m (10 ft) or 10 percent of the circuit length figured
at the higher ampacity, whichever is less.
 
wirebender said:
:-?

310.15(A)(2) Selection of Ampacity Where more than one calculated
or tabulated ampacity could apply for a given circuit length,
the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent
portions of a circuit, the higher ampacity shall be permitted
to be used beyond the point of transition, a distance equal
to 3.0 m (10 ft) or 10 percent of the circuit length figured
at the higher ampacity, whichever is less.
Click to expand...

Is it me, or is this poorly worded?
 
You have a wireway with 10 conduits entering the top, each have 9 CCC.

In the back of the wireway you have 10 conduits that line up with the top.

So you have 90 CCC total, but the wires run from top conduit to back conduit

directly below it. Do you need to derate at all ? I say 'no' because nothing

crosses.
 
Quote:
Originally Posted by wirebender


310.15(A)(2) Selection of Ampacity Where more than one calculated
or tabulated ampacity could apply for a given circuit length,
the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent
portions of a circuit, the higher ampacity shall be permitted
to be used beyond the point of transition, a distance equal
to 3.0 m (10 ft) or 10 percent of the circuit length figured
at the higher ampacity, whichever is less.

Is it me, or is this poorly worded?
__________________
Lou





I'll go for the poorly worded notion.
With the word transition, I take this to mean passing thru areas with higher temperature, and the adjustment of ampacity because of ambient temperatures.
 
wirebender said:
:-?
310.15(A)(2) Selection of Ampacity Where more than one calculated
or tabulated ampacity could apply for a given circuit length,
the lowest value shall be used.
Exception: Where two different ampacities apply to adjacent
portions of a circuit, the higher ampacity shall be permitted
to be used beyond the point of transition, a distance equal
to 3.0 m (10 ft) or 10 percent of the circuit length figured
at the higher ampacity, whichever is less.
Click to expand...

Maybe I shouldn't try to commit the entire code to memory... :grin: :grin: :grin: I thought he was talking about 310.15(B)2..... Not sure how it would effect the determination due to derating. The exception in 310.15(A)2 does seem to be in conflict - but does not exempt you from de-rating IMO. Only an exemption for which ampacity to derate...

Although Handbook commentary is not part of the code they do have an example:
Three 500-kcmil THW conductors in a rigid conduit are run from a motor control center for 12 ft past a heat-treating furnace to a pump motor located 150 ft from the motor control center. Where run in a 78?F to 86?F ambient, the conductors have an ampacity of 380 amperes, per Table 310.16. The ambient temperature near the furnace, where the conduit is run, is found to be 113?F, and the length of this particular part of the run is greater than 10 ft and more than 10 percent of the total length of the run at the 78?F to 86?F ambient. Determine the ampacity of total run in accordance with 310.15(A)(2).
Solution
In accordance with the correction factors for temperature at the bottom of Table 310.16, the ampacity is 0.82 ? 380 amperes, or 311.6 amperes. This, therefore, is the ampacity of the total run, in accordance with 310.15(A)(2).
Had the run near the furnace at the 113?F ambient been 10 ft or less in length, the ampacity of the entire run would have been 380 amperes, in accordance with the exception to 310.15(A)(2). The heat-sinking effect of the run at the lower ambient temperature would have been sufficient to reduce the temperature of the conductor near the furnace.
Click to expand...
 
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