backfeed breaker

[624]

I have a grid tied inverter, installation has follows 40 amp in man ran to a solar only sub panel with a plug in type 40 amp acting has main in subpanel with (2) 20 amp solar ckts micro inverters. inspecter says i need a hold down kit on my 40 amp in main he is referring to thank you

 

[624]

I have a grid tied inverter, installation has follows 40 amp in man ran to a solar only sub panel with a plug in type 40 amp acting has main in subpanel with (2) 20 amp solar ckts micro inverters. inspecter says i need a hold down kit on my 40 amp in main he is referring to thank you

forgot to post nec code ahj is referring to 2020 nec408.36(d.

 

[don_resqcapt19]

Ask him to look at 705.12(E).

 

[suemarkp]

The inspector may be right. It sounds like there is a 40A feeder from main to subpanel. That subpanel has two solar inputs through 20A inverter circuits. Per 705.12(E), I think you can argue that the 20A circuits don't need to be held down nor does the 40A backfeed in the main panel. But that 40A feeder to the solar subpanel is just like any other subpanel main connection and in this case it is a backfed main. So if I understand things right, it needs a hold down.

What I don't understand is why that subpanel even has a main? Couldn't it be eliminated and just terminate the 40A feeder on the main lugs?

 

[ggunn]

The inspector may be right. It sounds like there is a 40A feeder from main to subpanel. That subpanel has two solar inputs through 20A inverter circuits. Per 705.12(E), I think you can argue that the 20A circuits don't need to be held down nor does the 40A backfeed in the main panel. But that 40A feeder to the solar subpanel is just like any other subpanel main connection and in this case it is a backfed main. So if I understand things right, it needs a hold down.

What I don't understand is why that subpanel even has a main? Couldn't it be eliminated and just terminate the 40A feeder on the main lugs?

The reason for the hold down requirement is to keep a backfed breaker from staying energized if it can be pulled out of the panel it is in, and UL1741 prevents PV inverter output circuits from being energized when there is no connection to an AC voltage source, hence 705.12(E). IMO, this covers all the breakers from a PV system back to the service as long as there are no other sources that can feed the conductors.

 

[don_resqcapt19]

The inspector may be right. It sounds like there is a 40A feeder from main to subpanel. That subpanel has two solar inputs through 20A inverter circuits. Per 705.12(E), I think you can argue that the 20A circuits don't need to be held down nor does the 40A backfeed in the main panel. But that 40A feeder to the solar subpanel is just like any other subpanel main connection and in this case it is a backfed main. So if I understand things right, it needs a hold down.

What I don't understand is why that subpanel even has a main? Couldn't it be eliminated and just terminate the 40A feeder on the main lugs?

I missed the main part of the question.

I agree that the main needs a hold down because it is connected to a supply on the line side that is not an utility interactive source and one that will stay energized even if it becomes disconnected from the bus, unlike the breakers fed from the inverter where the source will shut off if the breaker becomes disconnected from the bus.

 

[ggunn]

I missed the main part of the question.

I agree that the main needs a hold down because it is connected to a supply on the line side that is not an utility interactive source and one that will stay energized even if it becomes disconnected from the bus, unlike the breakers fed from the inverter where the source will shut off if the breaker becomes disconnected from the bus.

Sorry, I missed that the MCB in the subpanel is side mounted. Yes, it needs to be held down whether or not PV is installed in the sub.

 

[solarken]

The inspector may be right. It sounds like there is a 40A feeder from main to subpanel. That subpanel has two solar inputs through 20A inverter circuits. Per 705.12(E), I think you can argue that the 20A circuits don't need to be held down nor does the 40A backfeed in the main panel. But that 40A feeder to the solar subpanel is just like any other subpanel main connection and in this case it is a backfed main. So if I understand things right, it needs a hold down.

What I don't understand is why that subpanel even has a main? Couldn't it be eliminated and just terminate the 40A feeder on the main lugs?

I agree, move the sub panel feeder to the main lugs and get rid of the 40A breaker used as main, is an alternative.