When is a neutral required in a 3ph system? Solar PV

[DattMtn]

I have been in a debate with our EOR about when we will need to have a neutral on our solar PV sites. I understand that there are inverters that may need a neutral for sensing purposes and can be downsized to the EGC as per 705.95(B), and some inverters don't need a neutral at all. What we are running into is that we have 3ph 3W circuits running out to the AC Combiner panels and that wouldn't be a problem until we have Data Acquisition loads on that panel board that are 2ph Line to Line. While this load is small it will be unbalancing the phases and in my opinion would necessitate a neutral run to this panel. I have been scouring the code trying to find when a neutral conductor becomes a requirement. I noticed 220.61 gives a little more information on this but not a clear cut answer on when it would be a requirement. Are there any other NEC articles I could reference for neutrals? In the past I have worked on other projects that have had more significant unbalanced loads (tracker motors, lighting, ev chargers etc.) and feel like those would most certainly require the neutral but here because the unbalanced load is fairly light (1-2A) I am not sure what the impact would be if we did not install a neutral.

 

[jaggedben]

You are correct that if you want to install an L-N load in a panel you would have to bring a neutral to that panel. The NEC does not allow current on an EGC. It would be a violation of 250.6 and 250.24(A)(5).

 

[jaggedben]

What exactly is not clear cut enough for you in 220.61?

 

[jaggedben]

See also 215.2(A)(2).

 

[jaggedben]

Perhaps a small transformer to power your data acquisition equipment.

 

[electrofelon]

You are correct that if you want to install an L-N load in a panel you would have to bring a neutral to that panel. The NEC does not allow current on an EGC. It would be a violation of 250.6 and 250.24(A)(5).

But op said line to line. Unless that was a typo, as it's hard to see how a neutral that has nothing connected to it would balance something out? Perhaps I am misunderstanding the concern?

 

[jaggedben]

I totally missed that detail. Oops. Everything I said erroneously assumed the small load was L-N.
Since it's L-L I see no reason to run a neutral.

 

[DattMtn]

Yes the AUX load has an optional power supply for L-L. What I have been concerned about in this scenario is that if you put together a panel schedule, there would be one phase that would have less VA than the others, thus an unbalanced phase and the need for a return path. Is my concern misplaced as there are plenty of unbalanced 3ph systems out there without a neutral or would this necessitate a neutral as I have been debating.

 

[wwhitney]

What I have been concerned about in this scenario is that if you put together a panel schedule, there would be one phase that would have less VA than the others, thus an unbalanced phase and the need for a return path.

Sure, but that return path is one of the L conductors. A neutral can't be a return path if nothing is connected to it.

Is my concern misplaced

Basically yes.

Cheers, Wayne