310.15(b)(7) and derating

[kwired]

Neutral doesn't need to be same size as the ungrounded conductors in many cases. The more "line to line" loads you have the less neutral load you will have to account for. Say you have 100 amp feeder and 40 amps of straight 208 volt loads, there is no reason your neutral should need to be more than 60 amps out the starting gate. The clueless inspectors out there probably won't see it this way though

 

[infinity]

I really don't think you're concerns are justified. What are the chances of "maintenance or servicing" needing to be done on one of the common neutrals? You can say that about anything. What is the difference between having a single service or distribution panel feeding multiple units? It's the same thing if the service or distribution panel or feeder needed servicing. Besides you have multiple feeders in the same conduit if something goes wrong or needs rerouting or servicing they all need to go down anyway. I think you are overthinking this.

I agree, shouldn't really be an issue. Worst case scenario is you need to shut down 3 panels to work on the feeder neutral.

 

[electrofelon]

I would be more likely to use something that taps the main run without cutting it as much as possible, or at least an irreversible splice method if reducing the run after the tap. Somebody that has no business doing so will otherwise open the neutral under load someday.

Why is everyone worried about these preposterous scenarios in this situation? Again, the neutral in a regular feeder or service is no different - even 'much worse' - and you could come up with all sorts of scenarios about people breaking it under load and messing everything up downstream or it needing servicing.

 

[kwired]

Why is everyone worried about these preposterous scenarios in this situation? Again, the neutral in a regular feeder or service is no different - even 'much worse' - and you could come up with all sorts of scenarios about people breaking it under load and messing everything up downstream or it needing servicing.

Well yes, I sort of had that feeling back when they wanted handle ties on all MWBC's, let those that don't know any better burn their stuff up, then maybe they will learn to call in someone that does know what they are doing. I kind of don't feel sorry for people that land 120 volt circuit on high leg slot in a breaker panel either, especially if a lot of the panel has open spots on every third position. I certainly don't need to see orange markings to know what is up, and still seen cases where it didn't matter, even when a "professional" missed what was up.

Long time ago now and I was still fairly green apprentice, but a EC from outside the area did some work in local school (had high leg delta service) They moved some things around to make room for their feeder (they were associated with an elevator installation). We got called because many items in kitchen were not working - found out we had 208 volts on wrong leg. I didn't talk to anyone from that other EC but according to my boss sounded like they never heard of such a system. Was in summer and school was out, or it could have been even more items destroyed. Mostly effected some lights and maybe a refrigerator or two that were lucky enough to be on the wrong phase.

 

[Adamjamma]

Sorry, that was a typo I meant to say 120/208 single phase in post #32. Someone will correct me if I am wrong, but I do not believe you could meter these separately where there is only a common neutral available - you would need to meter at the point where there is an individual neutral for each metered circuit.

Maybe I am wrong, but, in the case of the three meters, they can share the ground, from the ground rod to the individual main panels, as it is for faults between the main panels and the meters to the single ground rod. So, you are carrying only two lve and one neutral for each meter, to its individual panel, which is treated a main panel. It would be harder if one was required firefighter disconnects as they normally become the neutral ground point and the panels then get treated like sub panels, at least where I am.
Using metal conduit, with a ground wire added, is n problem that I can see.