Generator Interlock and solar backfeed breaker

[Sparkey1981]

Searched the forum and got some answers but just so I am clear a residential 200 amp panel with solar back feed breaker adding a generator interlock is a no go ?
Thanks

 

[rnatalie]

Grid-tie inverters usually provide the interlocking themselves and shut down when the utility power goes away. No interlock is required.

 

[Sparkey1981]

Grid-tie inverters usually provide the interlocking themselves and shut down when the utility power goes away. No interlock is required.

so what stops the solar from back feeding the generator if the solar back feed breaker was left on ? I assume once inverter see's power from generator it will try to power on?

 

[GoldDigger]

You are correct that if the generator provides a stable enough waveform for the inverter to qualify it as grid power, then it is possible that the inverter will try to backfeed the generator if the load drops too low. The simplest way to deal with that is to simply disconnect the solar when switching to generator. It might be difficult to provide a foolproof interlock for the backfed breaker though. If the solar breaker and the generator inlet breaker were adjacent it would not be too difficult. But the generator inlet needs to be adjacent to the main for interlock and the solar will typically be at the other end of the bus.

 

[Sparkey1981]

You are correct that if the generator provides a stable enough waveform for the inverter to qualify it as grid power, then it is possible that the inverter will try to backfeed the generator if the load drops too low. The simplest way to deal with that is to simply disconnect the solar when switching to generator. It might be difficult to provide a foolproof interlock for the backfed breaker though. If the solar breaker and the generator inlet breaker were adjacent it would not be too difficult. But the generator inlet needs to be adjacent to the main for interlock and the solar will typically be at the other end of the bus.

Correct the back feed for the PV system is at the bottom of the bus. This customer may need a 10 circuit transfer switch instead of interlock.

 

[rnatalie]

I miss understood the question. I thought you were using a generator interlock to try to avoid back feeding the UTILITY with the solar (as if the solar tie was a generator).

 

[GoldDigger]

Correct the back feed for the PV system is at the bottom of the bus. This customer may need a 10 circuit transfer switch instead of interlock.

That would be a good alternative.

 

[PeterOven]

Move the solar to the supply side of the service disconnect, then you can have the interlock kit on the panel. NEC 2017 230.82(6) (sorry don't have my 2020 with me).