derating conductors in a theater

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rainrider

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hello I'm new to this so I'm not sure how this is all suppose to sound, so here goes!
Theaters 520.6 says "the 30 conductor limit of 366.6 and 376.22 shall not apply."
metal wireway 376.22 says you don't have to start derating until you reach 30 conductors. After 30 you fall back to using the table 310.15b for derating.
auxilirary gutters 366.6 is the the same.
Now does this mean that I don't have to derate at all or does it mean I have to start derating like you would with conduit.
"30 conductor limit shall not apply"
I've got about 350 current carrying conductors (theater lights off dimmers racks) running through 8 by 8 wireway. Do I pull #8s or #12s?
Thanks
 
Re: derating conductors in a theater


I've got about 350 current carrying conductors (theater lights off dimmers racks) running through 8 by 8 wireway. Do I pull #8s or #12s?
Thanks
Click to expand...
Rainrider,
I'm not sure I'm understanding your post.Are you saying this is one 8x8 wireway? Or wireway(s)..
 
Re: derating conductors in a theater

My take is that you do not have to derate, just make sure that the conductors do not exceed 20% of the interior cross sectional area of the auxilary gutter or wireway. And note the wording that this is for "border or stage pockets circuits or for remote-control conductors. IMO, 520.6 is saying you do not have to worry about the 30 conductor derating found in 366.6 and 376.22. :)
 
Re: derating conductors in a theater

Very cool! Dillon3c I've got one 8 by 8 gutter about 100ft long running from a dimmer room out to catwalks above the stage.
wirenut1980 Thats our take too,but I've consulted with other wiremen that have done theaters and there saying I have to derate. I've run this by our local inspector and he is reading like you are, no derating. Obvousally my boss woulld rather use #12s then #8s. I just want to be sure. This issue has created some good debate in our crew shack and has umtiamally brought me here.
Im good with the 20% fill with #8s (tight) and real good with the #12s.
Thanks guys
 
Re: derating conductors in a theater

I tend to read that section as requiring derating starting with the 4th conductor. The "30 conductor" rule in 366.6 acts as an exception to 310.15(B)(2)(a) and so when 520.6 removes the "30 conductor" rule, then derating starts with the 4th conductor.
Don
 
Re: derating conductors in a theater

If you look at the 2002 Handbook and the commentary after 520.42, it says ...The derating factors if 310.15(B)(2)(a) are judged unnecessary because the conductors are not all energized at one time, and are not often energized at full intensity (dimmed), and are not energized continuously. It seems there is experience that derating is unnecessary.

I have always interpreted this section to also require 125 C insulation, not the usual THHN when you are up in the space around the lights. What type of wire insulation do you plan to use?
Jim T.
 
Re: derating conductors in a theater

Don, that is definately a possibility too. I didn't think of it that way! I guess my question now is: in Section 520.6 are we talking about power circuits, or control circuits (i.e. what kind of current is going through these conductors and how much heat is coming from them)? It says in the NEC "stage pocket circuits or remote-control conductors." I'm afraid I do not know what stage pocket circuits are.
 
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