Say you have two j-boxes, A and B. The hot and neutral of a lighting circuit comes into A, goes to B and proceeds further where it feeds a switch. The switch leg makes a circular path around the ceiling, comes back to B by another route than the hot, goes thru B to A and leaves A by a route other than the original hot feed came in. Would you require there to be a designated "hot" neutral and a designated "switch leg" neutral in the conduit between A and B? If you used the original neutral that came thru with the hot between A and B to also serve as the neutral for the switch leg, since they are actually the same neutral, would you in reality create some kind of neutral loop that would balance and divide the current between the load on that switch leg and any other load that happened to be downstream of the switch? A break time breakfast is riding on this.
An interesting question, but if I understand you correctly, I would say no. The neutral would not "suffer" any "loop" problems unless you introduced another hot circuit. Even then, I haven't drawn in out, but I see no problems, except for some routing that is unnecessarily complicated.
Anybody else with a differing opinion? Would love to hear the other side...
To be sure it's understood, I'll try to clarify if I can. There is a straight line run of conduit feeding a lighting circuit from a panel to jbox A, jboxB and the switch for the lights. The switch leg comes from the switch in mc and feeds a row of lights. At the end of the row it loops over and feeds the next row and at the other end of the row goes to B. For convenience sake, the switch leg goes through the conduit that carries to A. From A it feeds mc to the last row of lights. I say that you need two neutrals in the conduit from A to B to keep it seperate even though it is the same neutral.