Parallel Feeders

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bnewport

bnewport

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Indiana
I am looking for clarification on Article 310.4 - Conductors in parallel. The NEC states that the paralleled conductors must be the same length. To what extent does this apply? In my humble opinion, this is not always practical. For instance: 10 parallel runs of 600KCM feeders. The raceway distances will vary to some degree, due to 90's, etc. This makes for different lengths on the ends. Some of our service techs say that all of the conductors must be exact length down to the 1/4 inch!!! If you consider that the resistance of 600KCM is only 0.02 ohms/kFT, it seems ridiculous to think that 1" of wire length would make a large enough current imbalance / Vd to make a difference! When these feeds are terminated, lets say on a breaker, how do you comply with NEC 110.12? I have seen people terminate cables and have the difference in conductor length just wadded up in the panel!

Any help would be appreciated! I am looking for code sections, as well as the calculations to show what the difference would be if the conductors were slightly different. Does anyone else get tired of the "that's just how we have always done it..." song and dance???

Question everything-

Thanks-
Bryan
 
Re: Parallel Feeders

Bryan It is helpful in these cases to understand the theory behind the rule. As you can see from the links Don posted, the length needs to be close. What I do is roll them out on the ground and cut them the same length. Then if they are cut after being pulled in, I try to cut off the same length from each.
 
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