Solar Overcurrent Protection

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Kjc59

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Audubon, NJ
I am no solar expert so I’m hoping someone is. I have a 4,000 switchboard and a 317kW PV system will be tied into a breaker in the board. I am pretty sure the breaker in the switchboard needs to be 1,200 Amps. Is this system too large for a 4,000A board? Size up buswork? To me I would think the ideal install would be ahead of everything but that is not the constraints I’m working with. Any feedback?


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Kjc59 said:
I am no solar expert so I’m hoping someone is. I have a 4,000 switchboard and a 317kW PV system will be tied into a breaker in the board. I am pretty sure the breaker in the switchboard needs to be 1,200 Amps. Is this system too large for a 4,000A board? Size up buswork? To me I would think the ideal install would be ahead of everything but that is not the constraints I’m working with. Any feedback?


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125% of your total inverter current cannot exceed 800A for a load side connection to a 4000A panelboard. You should interconnect the PV on the supply side of the main service OCPD.
 
You can do it either by following ggunn with the 120% rule or doing it under engineering supervision without the 120% limitation. In my opinion it's always better to do a load side connection if that is possible, but a supply side is also an option.
 
jaggedben said:
There are possibilities beyond the 120% rule these days, but you need to fully read 705.12 or understand about Power Control Systems.
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I wish that 705.12(B) had a line that included PCS as a specified alternative to comply. There is a bit of hand waving around it right now. 705.13 says PCS can be used to limit current and loading on busbars but not how that is used to comply with 705.12(B). It looks like PCS is only allowed in connection with the engineering supervision allowed by 705.12(B)(6).
 
wwhitney said:
Seems to me that means it can be used to limit the current values used as input to any of the compliance checks in any of the methods of 705.12(B).

Cheers, Wayne
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There is that implication and I'm sure people are doing that. But it is not listed as one of the ways to comply with 705.12(B) and I wish it were, to provide better guidance to AHJs.
 
pv_n00b said:
There is that implication and I'm sure people are doing that. But it is not listed as one of the ways to comply with 705.12(B) and I wish it were, to provide better guidance to AHJs.
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The 2020 and 2023 NECs both refer to using the PCS inputs in 705.12, in different ways. 2020 mentions it directly at the beginning of 705.12, and 2023 does it by referencing 705.28(A), which in turn mentions EMS.
 
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