I have a local inspector who is now requiring all typical 4 wire feeders and services to be de-rated by 80% per 310.15A3. By a typical, I mean any 208/120V or 480/277V 3 phase 4 wire service must be de-rated for having 4 wires in a single conduit.
In the past, I have normally used the exception, 310.15 A 5 a, for a neutral conductor that only carries the unbalanced current of the 3 phases. But now the inspector seems to think this exception can never (or almost never) be used.
He says he has talked to engineers and the ICC about this and they all agree. It seems like that opinion must be coming from the word "only" in 310.15A5a:
"A neutral conductor that carries ONLY the unbalanced current from the other conductors of the same circuit shall not be required to be counted..."
Apparently, with this interpretation, anytime a conductor carries ANY harmonics, and not just a majority of harmonics, the conductor is carrying something other than an unbalanced current, and it must be counted for derating.
I don't think that was ever the intent to require counting a neutral just because it carries some harmonics, otherwise why would A5b state a "majority" of harmonics, which most people consider 51% or more.
Does anyone else agree with this interpretation, or does anyone else have anyone enforcing this?
In the past, I have normally used the exception, 310.15 A 5 a, for a neutral conductor that only carries the unbalanced current of the 3 phases. But now the inspector seems to think this exception can never (or almost never) be used.
He says he has talked to engineers and the ICC about this and they all agree. It seems like that opinion must be coming from the word "only" in 310.15A5a:
"A neutral conductor that carries ONLY the unbalanced current from the other conductors of the same circuit shall not be required to be counted..."
Apparently, with this interpretation, anytime a conductor carries ANY harmonics, and not just a majority of harmonics, the conductor is carrying something other than an unbalanced current, and it must be counted for derating.
I don't think that was ever the intent to require counting a neutral just because it carries some harmonics, otherwise why would A5b state a "majority" of harmonics, which most people consider 51% or more.
Does anyone else agree with this interpretation, or does anyone else have anyone enforcing this?