PV back feed breaker location, Why?

G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Fred B said:
But what you are doing is adding the PV as if it is a load, limiting it by combining it with the other loads not exceeding the bus capacity. Not even looking at actual loads but each breaker capacity.
705.12(B)(3)
(3) The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar. The rating of the overcurrent device protecting the busbar shall not exceed the rating of the busbar. Permanent warning labels shall be applied to distribution equipment displaying the following or equivalent wording


Even using this method you will not get a net metering in excess of usage for POCO to owe customer.
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Read 703.12(B) more carefully. The numbered sections after it are options, not inclusive requirements. You only need to comply with one of them ,i.e., It's an "or", not an "and". The one you are quoting is the one we typically use for AC inverter combiner panels. It is virtually never used to qualify the bus in a service panel.
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
ggunn said:
The numbered sections after it are options, not inclusive requirements. You only need to comply with one of them ,i.e., It's an "or", not an "and".
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I understand that, thank you. Most time I see either a Supply side tap or the opposite end of bus back feed.

ggunn said:
The one you are quoting is the one we typically use for AC inverter combiner panels.
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Most every combiner panel I've seen will have label that says "For PV only, No other loads". So how does condition in 705.12(B)(3) apply to combiner panel?
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Saw answer on anther post that seems to Give answer as to why it work. Thanks.
Now I see what you were indicating @ggunn. Sorry so stupid.

120% panelboard question

I have been asked if the backfeed breaker must always in all circumstances be placed at the furthest point on the bus from a main breaker (or lugs in case of a sub). This comes up because some of the jobs we're seeing have ample electrical space available, like say a 225A bus with a 175A main...
forums.mikeholt.com
 
G

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Fred B said:
I understand that, thank you. Most time I see either a Supply side tap or the opposite end of bus back feed.


Most every combiner panel I've seen will have label that says "For PV only, No other loads". So how does condition in 705.12(B)(3) apply to combiner panel?
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For systems installed under NEC versions before the language in 2023 NEC 705.12(B)(3) was put into the code in 2014, AC combiners were frequently labeled that way because they skirted compliance and AHJs let them slide as long as there were no loads in the panel. Since then, loads are permissible in inverter AC combiners as long as they comply with 705.12(B)(3).

That said, there may be other reasons an AC combiner is labeled that way, one of which may be that there is no more electrical room in the panel. Another is that the AHJ may have their own requirements that make it necessary.
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
ggunn said:
That said, there may be other reasons an AC combiner is labeled that way, one of which may be that there is no more electrical room in the panel. Another is that the AHJ may have their own requirements that make it necessary.
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Another common possibility is the labels are incorrect. Around here everyone slaps on just about every conceivable label because they don't know which one is the corry one and/or just want to cover all possibilities for inspectors who don't know.
 
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