Applying 310.15(B)(7) w/ PV

[HoosierSparky]

I have a 200A load center being fed by a 175A MCB and 60A from a PV system. Can 310.15(B)(7) be applied to the MCB panel feeders? I'm sayin no, due to during the day when the PV system is pumping 60A into the panel there COULD be 175A total on the feeders. I'm still working under the 2014 NEC.

 

[jaggedben]

I hope I'm understanding your question correctly. If so, I don't think you're logic makes any sense.

If the feeders are protected by a 175A breaker, then that's the max that's going to flow on the feeder, period.
The PV may reduce the flow of current on the feeder, by taking care of the load. They may send a much lesser amount of current back the other way, if the PV exceeds the load. But the PV will not increase the load on the feeder in any way.

So...
Whatever you think of the logic behind 310.15(B)(7), the PV has no effect on that logic whatsoever.

 

[GoldDigger]

On the other hand a load wired to the middle of the feeder could draw the sum of the two source currents. Same problem that affects a panel with backed breakers.
It still would not result in excess current in either part of the original feeder, of course.

Sent from my Pixel 4a using Tapatalk

 

[HoosierSparky]

OK. I might not have written exactly what I was thinking. Here is a similar situation:




The proposed sizing is @ 12 - 2/0 and at 13 - #1. I think my corrections would be correct. The situation @ 12 is the same on my original post, except they have reduced the MCB to 175a and 1/0 feeders. They are applying 310.15(B)(7).

 

[Hv&Lv]

So they are saying 175A X .83 and using a 2/0 based on 145 amps @60c after rounding down.

 

[HoosierSparky]

So they are saying 175A X .83 and using a 2/0 based on 145 amps @60c after rounding down.

Correct.

 

[wwhitney]

In the diagram you posted, 310.15(B)(7) would apply to (12) but not to (13).

Cheers, Wayne

 

[HoosierSparky]

So they are saying 175A X .83 and using a 2/0 based on 145 amps @60c after rounding down.

Thanks Wayne.