parallel conductors
- Thread starter vanwalker
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- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: parallel conductors
Here?s my answer to the question you asked:
You include the neutral (for the purposes of derating) only if there is a significant amount of harmonics present in the system. You would have to determine whether the amount of harmonics is ?significant.?
Here?s my answer to the question you didn?t ask:
Back up another half step. If you are talking about a service whose calculated load is 400 amps, then you cannot use two sets of 250 MCM AL in a single conduit. Even at 80% derating, and even with a 90C rated conductor (you didn?t tell us what type of conductor you had), a pair of 250 AL is only good for 368 amps. You might say that a 400 amp breaker is the next higher standard size. That would be true, but irrelevant. The conductor has to be rated for every bit of the calculated load. In other words, the calculated load would have to be under 368 amps, or else you must use larger service conductors.
You should first calculate the load, per article 220. If you do not have that calculation, and if you are putting in a 400 amp panel (with a 400 amp main breaker), then the service conductors must be rated at least 400 amps.
Here?s my answer to the question you asked:
You include the neutral (for the purposes of derating) only if there is a significant amount of harmonics present in the system. You would have to determine whether the amount of harmonics is ?significant.?
Here?s my answer to the question you didn?t ask:
Back up another half step. If you are talking about a service whose calculated load is 400 amps, then you cannot use two sets of 250 MCM AL in a single conduit. Even at 80% derating, and even with a 90C rated conductor (you didn?t tell us what type of conductor you had), a pair of 250 AL is only good for 368 amps. You might say that a 400 amp breaker is the next higher standard size. That would be true, but irrelevant. The conductor has to be rated for every bit of the calculated load. In other words, the calculated load would have to be under 368 amps, or else you must use larger service conductors.
You should first calculate the load, per article 220. If you do not have that calculation, and if you are putting in a 400 amp panel (with a 400 amp main breaker), then the service conductors must be rated at least 400 amps.
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