How Many feed back PV breakers per Panel?

[ING23]

I was just trying to piece together what the AHJ might be saying so that you can better prepare to debate them or make a revision to get a fast approval.

In this case, it would be easier to verify the panel's busbar rating of 225A and then just use (a). Then you could see if the AHJ approves it. I think they are just interpreting the 120% rule incorrectly or differently than usual. It might be more difficult to get them to see it your way than it would be to adapt and move on.

If the busbar is not 225A, then I would just put in a PV combiner breaker panel next to the service panel. It shouldn't add much of a cost.

The bus bar is 200A and I am going to derate the main breaker from 200 A to 175A in order to comply with the 120% rule
30A ( New PV System) + 20A (Old PV System) + 175A < 200 x 1.2
225A < 240A

 

[ggunn]

Oh you can argue with it, and sometimes you should. Making up rules that aren't in the code isn't the same as interpreting rules that are there.

I agree, but there are a couple of different scenarios. One is where an inspector is capriciously making rules up when something just "doesn't look right" to him; in that case challenge it or not depending on whether it is a fight worth having. The other is where the rules are published by the AHJ in something like an "Interconnection Guidelines" document; in that case you almost certainly will not prevail.

 

[Elect117]

The bus bar is 200A and I am going to derate the main breaker from 200 A to 175A in order to comply with the 120% rule
30A ( New PV System) + 20A (Old PV System) + 175A < 200 x 1.2
225A < 240A

Your math isn't correct but it sucks that the bus bar is not rated 225A.

Don't forget about the 125%. Also, it is based on the supply current, not the OCPD.

Agree, l am going to use a Load Center to combine the Old and the New PV system ending in One PV breaker at the Main Panel .
Just some thoughts I think , regardless of how many subpanel you have down string from the Main panel , you have to comply with the 120% rule as you mention before . Thanks for the advise (choose my battles.)

This is probably the best method, but make sure you are using the rule correctly.

P.S. There are other rules for load side connections that might be easier to met. It just depends on your set up.

 

[wwhitney]

Your math isn't correct but it sucks that the bus bar is not rated 225A.

Don't forget about the 125%. Also, it is based on the supply current, not the OCPD.

You are assuming the 20A and 30A are inverter output currents. But that is unspecified in what you quoted; and as they correspond to standard breaker sizes, then it is more likely they are standard breaker sizes.

And those breaker sizes are required to be at least 125% of the inverter output current. So adding them up, instead of using 125% of the inverter output current, is a conservative overestimate. If that overestimate is less than the busbar rating, the 120% rule is complied with.

But yes, using the actual inverter output currents could give you a sharper estimate; if the inverter output currents are 16A and 24A, respectively, it will make no difference. Whereas if they happen to sum to at most 32A, then the OP wouldn't need to downsize the main breaker from 200A to 175A.

Cheers, Wayne

 

[ING23]

Your math isn't correct but it sucks that the bus bar is not rated 225A.

Don't forget about the 125%. Also, it is based on the supply current, not the OCPD.



This is probably the best method, but make sure you are using the rule correctly.

P.S. There are other rules for load side connections that might be easier to met. It just depends on your set up.

You are assuming the 20A and 30A are inverter output currents. But that is unspecified in what you quoted; and as they correspond to standard breaker sizes, then it is more likely they are standard breaker sizes.

And those breaker sizes are required to be at least 125% of the inverter output current. So adding them up, instead of using 125% of the inverter output current, is a conservative overestimate. If that overestimate is less than the busbar rating, the 120% rule is complied with.

But yes, using the actual inverter output currents could give you a sharper estimate; if the inverter output currents are 16A and 24A, respectively, it will make no difference. Whereas if they happen to sum to at most 32A, then the OP wouldn't need to downsize the main breaker from 200A to 175A.

Cheers, Wayne

The 20A and 30A are the breakers just protecting the Wire from the Inverter . They had been calculated to support the 125% of the Inverter max Output current but I shouldn't be adding PV breakers and the Main breaker. I understand I have to work with the 125% of the Power Source Current plus the OCDP protecting the Bus bar (main Breaker) when my Connection point is on the opposite side of the busbar and there are loads in between.

 

[ggunn]

The 20A and 30A are the breakers just protecting the Wire from the Inverter . They had been calculated to support the 125% of the Inverter max Output current but I shouldn't be adding PV breakers and the Main breaker. I understand I have to work with the 125% of the Power Source Current plus the OCDP protecting the Bus bar (main Breaker) when my Connection point is on the opposite side of the busbar and there are loads in between.

If you are using the OCPD ratings (and of course if they are correctly sized) and it fits in the 120% rule then you are good, but the 120% rule is based on 125% of the inverter currents, not the OCPD ratings, so if you recalculate using those numbers it will very likely give you a bit more headroom.

 

[ING23]

If you are using the OCPD ratings (and of course if they are correctly sized) and it fits in the 120% rule then you are good, but the 120% rule is based on 125% of the inverter currents, not the OCPD ratings, so if you recalculate using those numbers it will very likely give you a bit more headroom.

You are right , that was another battle I had with another AHJ , they were using the OCPD of the PV system for calculating the 120% rule . They were more receptive and understand , but I had to show them labels and datasheet to prove my point

 

[Fred B]

What if instead of bus tap or back-feed breaker you use line (supply) side taps, from a combiner panel? What effect would that have on these calculations debates, 120%, 125%, how many disconnects, etc.?

 

[ggunn]

What if instead of bus tap or back-feed breaker you use line (supply) side taps, from a combiner panel? What effect would that have on these calculations debates, 120%, 125%, how many disconnects, etc.?

The rules in 705.12 are for load side PV interconnections; line side interconnections are governed by 705.11. That said, however, if a combiner panel is used to aggregate the outputs of multiple inverters, where the inverters enter the combiner panel are on the load side of the OCPD between the panel and the service conductors and are therefore under 705.12(B).

The main difference is that the only limit to the 705.11 connection between the combiner panel OCPD and the service conductors is "the size of the service" which is usually determined by the ampacity of the service conductors at the point of interconnection.

 

[ggunn]

...where the inverters enter the combiner panel are on the load side of the OCPD...

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