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Current carrying conductors #194503 06/05/10 10:25 PM
Joined: Jun 2010
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ckr1231 Offline OP
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When installing lighting circuits in a raceway from a panel to a contactor cabinet-- Do I have to count switch legs as current carrying conductors? There are 5 277V/20A hots and 5 switch legs and 1 ground in the same raceway. There are no neutral wires in this raceway.
Does this mean the ampacity of the conductors must be derated to 50 percent?


There are no bad trips. Only good conductors !!!
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Re: Current carrying conductors [Re: ckr1231] #194506 06/05/10 11:43 PM
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gfretwell Offline
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I don't really see any way out of it.


Greg Fretwell
Re: Current carrying conductors [Re: gfretwell] #194508 06/05/10 11:56 PM
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ckr1231 Offline OP
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I felt that because they where each the same circuit, I would only be counting 5 current carrying conductors.


There are no bad trips. Only good conductors !!!
Re: Current carrying conductors [Re: ckr1231] #194509 06/06/10 12:01 AM
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ckr1231 Offline OP
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If I can install a raceway not exceeding 24 inches- then I would not have to derate.
That is how I understand the code.


There are no bad trips. Only good conductors !!!
Re: Current carrying conductors [Re: ckr1231] #194512 06/06/10 03:08 AM
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gfretwell Offline
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The issue is the heat dissipated in the wire and it doesn't really matter which circuit they are on.
If "X" amount of current goes down one wire and comes back on another in the same pipe, the accumulated heat is double.

I have heard convincing arguments that when you have several conductors on the same circuit going one way and sharing the available current since they are paralleled you should not need to derate beyond one conductor for each circuit but the language is not there to allow it.
An example would be 10 100w can lights on the same 20a circuit but separate switches on the near end, going through a raceway. As a sanity check, you could only have one neutral coming back but each hot needs to be counted at 20a because that is the size of the O/C device. (11 current carrying conductors).


Greg Fretwell
Re: Current carrying conductors [Re: gfretwell] #194514 06/06/10 10:21 AM
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ckr1231 Offline OP
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Your reply makes perfect sense inregard to the heat being generated. I was not certain if one hot and one switch leg in the same raceway would be considered two current carrying conductors. At this point, my wire is only worth half it's value. I will change it !!

Thank you !!!!


There are no bad trips. Only good conductors !!!
Re: Current carrying conductors [Re: ckr1231] #194516 06/06/10 01:06 PM
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gfretwell Offline
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Just remember you can use the 90c column for THHN so on a 20a breaker you can use #10 at 50%.
It might even end up cheaper to run another raceway and split them up. Be sure you correctly pair them


Greg Fretwell
Re: Current carrying conductors [Re: gfretwell] #194518 06/06/10 07:51 PM
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Tesla Offline
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Realisticly you'll need a 1" pipe and #10 THHN/THWN-2/MTW...

The Code does not provide field electricians with an 'out' such that they can rejigger standards based upon their opinion or calculations.

That from time to time something is over engineered is balanced against the reality of the hazard of under engineering.

BTW, W a y back in the day -- everyone thought that if it worked it was safe. Then electrical fires were invented...

And the NEC was born.


Tesla
Re: Current carrying conductors [Re: Tesla] #194520 06/06/10 10:07 PM
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ckr1231 Offline OP
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This is a 3/4 conduit (EMT) about 26 inches long. Each circuit is drawing about 7 to 8 amps. This was done during a shut-down. I found it after the fact.


There are no bad trips. Only good conductors !!!

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