PV Systems and Panelboard Ratings

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jbravard

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Where connecting solar photovoltaics to a branch panelboard, does the NEC require that the sum of the panelboard load and the PV system circuit current not exceed the bus rating of the panelboard? If so, where is this found in the NEC?

For example, if a PV system with a circuit current of 100 amps is connected to a 400 amp panelboard, does the NEC require that the main breaker of the panelboard be limited to 300 amps so that the sum of the loads and PV circuit current do not exceed 400 amps?
 
Re: PV Systems and Panelboard Ratings

I'm confused. A PV system would be a supply, not a load.

Can you provide more details? Are you attempting to sell power back to a utility?
 
Re: PV Systems and Panelboard Ratings

I'm confused, too, but the people I'm working with say that this is the rule for PV systems. They are a PV installation company and both the business owner and his electrician say that this is how it's done. This system is small (9 kW on a three story commercial building) and I don't think they are selling back to the utility.

My initial thought on this is that the PV will reduce the amount of current on the panelboard. The conductors and breakers supplying the panelboard bus will only see the difference of the two currents. If this rule is true, however, it implies that the current (and thus, heating) on the bus will be increased by generating power onto the bus and that the bus will "see" the load current plus the PV current.
 
Re: PV Systems and Panelboard Ratings

PV doesn't reduce the load on the panelboard bus. And the bus doesn't

see the load current plus the PV current.
Click to expand...
The bus will always see the total load current. If the bus is fed from two sources the current supplied from the PV source will reduce the current supplied from the main breaker. But the total current on the bus remains the same.

It is a subtle but important difference. So if you have a 300A main breaker, and a 100A PV supply breaker, the current on the bus can be as high as 400A.

Steve ;)
 
Re: PV Systems and Panelboard Ratings

I'm readily admitting that all I know about alternative power I've read/researched, but never had a chance to install. (Dream house design in the sand/trashcan.)

What research I have done suggests that 100 amps from a PV system is unreal! On top of that, the inverter you'd need (unless I'm missing something) is friggin' huge! Looked around just now, found a grid-friendly inverter that outputs 10 amps at 240VAC at over $2000!

I am very interested in what you've got going on! :)
 
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