Metal Wireway conductor derating

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steve66

steve66

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Illinois
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Engineer
376.22 says you don't have to apply the derating factors of 310.15(B)(2) unless you exceed 30 conductors.

If I have a metal wireway with a divider in it (something like a wiremold 6000 series), can I put 30 conductors in each divided section without derating?

Steve
 
Re: Metal Wireway conductor derating

Jeff, if I am installing two separate runs of 4X4 square duct in intimate contact with each other, are they two separate runs or a single wireway with a divider? :D
 
Re: Metal Wireway conductor derating

Let?s take it back to basics. The purpose of derating is to protect the conductors? insulation systems. Too many nearby conductors, each running at their ?full? ampacity, will create so much heat that it may damage insulation. You prevent the damage by limiting the amount of current in each conductor.

If 30 conductors that fill no more than 20 percent of a wireway will not create enough heat to risk damage to each other, then they will certainly not pose a risk to the wireway next door. In the divided wireway that Steve has described, we know that neither side will overheat the other, simply because we know that neither side will overheat itself.

QED.
 
Re: Metal Wireway conductor derating

Originally posted by jeff43222: I suspect the AHJ will call that one wireway with an irrelevant divider, not two wireways.
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AHJs have been known, on occasion, to make their calls as they see them. This is one case in which both the AHJ and I can be looking at the same code article and making opposite assertions about its meaning. I don?t think I could win an argument, but I might be able to produce a signed and sealed drawing that shows this configuration, and that declares it to be acceptable.
 
Re: Metal Wireway conductor derating

Originally posted by iwire:
Jeff how can you have it both ways? :)
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Originally posted by charlie:
Jeff, if I am installing two separate runs of 4X4 square duct in intimate contact with each other, are they two separate runs or a single wireway with a divider? :D
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I'm glad I'm not the AHJ! I think charlie b is right: different people could very easily make different interpretations on this one.
 
Re: Metal Wireway conductor derating

I think both Iwire and Charlie B made excellent points for considering them 2 wireways. I also think it should be considered 2 wireways.

Steve
 
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