Derating required?

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wc86

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Massachusetts
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Electrician
In commercial buildings i often see panels with 2x 2" emt conduits longer than 24" with all the circuits running through up to a trough or giant junction box and then all the individual MCs or small EMTs. I have seen this installation pass many times no matter how packed the pipes going into the panel are with obvious derating issues. Is this just something inspectors generally overlook?
 
So as long as thr conduit leading to the panel is not greater than 10ft or 10% its okay?
 

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The key to applying the exception is the length of the stuffed conduit in relation to the total length of the circuit. FWIW we would always try to keep the raceways 24" or less to avoid having to consider derating. Also raceways 24" or less bumps you up from 40% to 60% fill so you can stuff in 50% more conductors.
 
Keep in mind to use the full 10 feet without adjustment you would need circuit length of 100 feet or greater.

If you only have a 30 foot long circuit then you are limited to 3 feet that is not subjected to adjustments.

Then it gets more complicated when all the circuits in the raceway are different lengths, some circuits may not need adjustment but others do.
 
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