It has been long practice to use a common neutral with 480/277 line to neutral only (277 VAC) roadway lighting fixtures. Additionally single pole breakers or fuses are utilized so if one leg or fixture experiences a failure the entire section of the highway lighting is not lost. Does section 225.7 still allow this type of installation or does 240.15 and 210.4 now make this a non-compliant installation with the 2011 NEC? Thank you advance for any assistance.
If any single pole breakers are on a portion of the circuit which is no longer an MWBC (individual neutral originates at the same point as the breaker or earlier) there would be no conflict. And if there are only single line to neutral loads, only a handle tie would be required, not a common trip.
But for safe maintenance, where the breakers are going to be used as disconnects, handle ties or opening the whole MWBC at an upstream point would be required. And the code seems to mandate handle ties.
