Grid tie PV with Generator back up/

Deltaforce said:
Need of nterlock for genny in situations of

IF you have a backfed breaker and want to make it idiot proof, you either have to change it to a supply side connection or put some sort contactor on the inverter output circuit.

702.6 mandate transfer equipment, interlock included
Click to expand...
FWIW, I am pretty sure that electrofelon knows all that.
 
Deltaforce said:
Need of nterlock for genny in situations of

IF you have a backfed breaker and want to make it idiot proof, you either have to change it to a supply side connection or put some sort contactor on the inverter output circuit.

702.6 mandate transfer equipment, interlock included
Click to expand...
I am having a hard time understanding what you are saying. I do not believe there is a code requirement to mechanically interlock out the inverter. Whether it is a good idea is another story.

Personally I would be fine with a contactor to drop out the inverter, and not have a mechanical interlock.
 
electrofelon said:
I am having a hard time understanding what you are saying. I do not believe there is a code requirement to mechanically interlock out the inverter. Whether it is a good idea is another story.

Personally I would be fine with a contactor to drop out the inverter, and not have a mechanical interlock.
Click to expand...
Thanks your forbearance
No interlocking of inverter
Interlocking of standby generator with utility
702.6 talks about that
For your 'Personally I would be fine with a contactor to drop out the inverter, and not have a mechanical interlock', it prevent parallel of standby generator and pv.
But it does not prevent parallel of standby generator and utility
For that interlocking of main breaker and standby generator required as per 702.6
 
Deltaforce said:
Thanks your forbearance
No interlocking of inverter
Interlocking of standby generator with utility
702.6 talks about that
For your 'Personally I would be fine with a contactor to drop out the inverter, and not have a mechanical interlock', it prevent parallel of standby generator and pv.
But it does not prevent parallel of standby generator and utility
For that interlocking of main breaker and standby generator required as per 702.6
Click to expand...
He isn't talking about not having an interlock separating the generator from the utility, just a means to prevent the PV system from connecting to the generator. Move the PV point of interconnection to the supply side, install an interlock on the main panel, and be done with it. Supply side PV interconnections are not difficult.
 
I was thinking of using a normally closed relay that opens if the generator has energized the back-feed breaker.
 
Deltaforce said:
But complex, approval utility side need etc
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Are you new to solar? Those of us who aren't do them all the time. They are not at all complex, and as for utility approval, you don't need special approval to do a 705.11 interconnection unless the POCO expressly denies them. Do your homework; look at their interconnection guidelines or make a phone call or two.

I have had very few encounters with POCOs for whom supply side PV interconnections are a concern. You have to do something to keep the generator separated from the PV, and every alternative we have discussed, not that there are many of them, are more complex than a supply side PV interconnection.
 
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ggunn said:
Are you new to solar? Those of us who aren't do them all the time. They are not at all complex, and as for utility approval, you don't need special approval to do a 705.11 interconnection unless the POCO expressly denies them. Do your homework; look at their interconnection guidelines or make a phone call or two.

I have had very few encounters with POCOs for whom supply side PV interconnections are a concern. You have to do something to keep the generator separated from the PV, and every alternative we have discussed, not that there are many of them, are more complex than a supply side PV interconnection.
Click to expand...
ggunn said:
Are you new to solar? Those of us who aren't do them all the time. They are not at all complex, and as for utility approval, you don't need special approval to do a 705.11 interconnection unless the POCO expressly denies them. Do your homework; look at their interconnection guidelines or make a phone call or two.

I have had very few encounters with POCOs for whom supply side PV interconnections are a concern. You have to do something to keep the generator separated from the PV, and every alternative we have discussed, not that there are many of them, are more complex than a supply side PV interconnection.
Click to expand...
Hard to believe it default way of doing
As more complex, more expensive
Make it last option when service panel too small to add pv breaker nec 120% rule
 
Deltaforce said:
Hard to believe it default way of doing
As more complex, more expensive
Make it last option when service panel too small to add pv breaker nec 120% rule
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You can believe it or not, but moving the PV to a supply side connection is a very common way to protect a generator when it comes in as a retrofit after PV is already installed on the load side. It's as simple as adding a fused disconnect and a tap to the service conductors; any experienced electrician can do it very easily. It's a little more expensive than just landing a PV breaker but not compared to the cost of a generator, and your customer should have had this explained to him before he bought the generator because he cannot leave the PV connected the way it is.

As we have told you repeatedly, you have to do something to protect the generator from backfeed from the PV system. You can move the PV to the supply side or you can add series contactors to the PV conductors. Either way there will be associated costs and complexity, and either way you will have to get access to the service conductors.

Your last assertion is a whole 'nother can of worms, but when the PV system cannot connect in the main panel because of 705.12 concerns you have just three options: move the PV connection to the supply side, downgrade the main breaker to make electrical room for the PV, or reduce the size of the PV system to fit. The third option is the most unlikely to appeal to a customer, but in my experience the other two are about equally used in residential settings.
 
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ggunn said:
You can believe it or not, but moving the PV to a supply side connection is a very common way to protect a generator when it comes in as a retrofit after PV is already installed on the load side. It's as simple as adding a fused disconnect and a tap to the service conductors; any experienced electrician can do it very easily. It's a little more expensive than just landing a PV breaker but not compared to the cost of a generator, and your customer should have had this explained to him before he bought the generator because he cannot leave the PV connected the way it is.

As we have told you repeatedly, you have to do something to protect the generator from backfeed from the PV system. You can move the PV to the supply side or you can add series contactors to the PV conductors. Either way there will be associated costs and complexity, and either way you will have to get access to the service conductors.

Your last assertion is a whole 'nother can of worms, but when the PV system cannot connect in the main panel because of 705.12 concerns you have just three options: move the PV connection to the supply side, downgrade the main breaker to make electrical room for the PV, or reduce the size of the PV system to fit. The third option is the most unlikely to appeal to a customer, but in my experience the other two are about equally used in residential settings.
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I just noticed that you are in India; the rules may very well be different there. Does India enforce the US NEC? Protecting the generator from backfeed from a PV system is physics rather than code, though.
 
ggunn said:
You can believe it or not, but moving the PV to a supply side connection is a very common way to protect a generator when it comes in as a retrofit after PV is already installed on the load side. It's as simple as adding a fused disconnect and a tap to the service conductors; any experienced electrician can do it very easily. It's a little more expensive than just landing a PV breaker but not compared to the cost of a generator, and your customer should have had this explained to him before he bought the generator because he cannot leave the PV connected the way it is.

As we have told you repeatedly, you have to do something to protect the generator from backfeed from the PV system. You can move the PV to the supply side or you can add series contactors to the PV conductors. Either way there will be associated costs and complexity, and either way you will have to get access to the service conductors.

Your last assertion is a whole 'nother can of worms, but when the PV system cannot connect in the main panel because of 705.12 concerns you have just three options: move the PV connection to the supply side, downgrade the main breaker to make electrical room for the PV, or reduce the size of the PV system to fit. The third option is the most unlikely to appeal to a customer, but in my experience the other two are about equally used in residential settings.
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A thorough understanding nec 705, 230 and 110 critical for safe and correct implement these solutions
Generator interlock kit arrangements nec 702.5 complied solution alternative to such complex solutions
Sequence of operation when grid down as
1)Main Breaker OFF: The homeowner manually switch off
This physically disconnect the entire main panel and pv breaker
2)PV System Shut Down: The PV inverter,
Shut down anti islanding feature nec 705.40
3)Generator Breaker ON: The homeowner now slide the interlock bar over and switch the generator breaker to "ON."
4)No Backfeed: Because the PV system already shut down and no producing power,
no possibility of it backfeed generator. The generator now sole power source for the panel.
 
Deltaforce said:
A thorough understanding nec 705, 230 and 110 critical for safe and correct implement these solutions
Generator interlock kit arrangements nec 702.5 complied solution alternative to such complex solutions
Sequence of operation when grid down as
1)Main Breaker OFF: The homeowner manually switch off
This physically disconnect the entire main panel and pv breaker
2)PV System Shut Down: The PV inverter,
Shut down anti islanding feature nec 705.40
3)Generator Breaker ON: The homeowner now slide the interlock bar over and switch the generator breaker to "ON."
4)No Backfeed: Because the PV system already shut down and no producing power,
no possibility of it backfeed generator. The generator now sole power source for the panel.
Click to expand...
The interlock kits I have seen are at the main breaker with the generator breaker at the same end of the bus. The interlock prevents the main breaker and the generator breaker from being ON at the same time, and the kit is just a metal plate attached to the breaker handles.

If your design is governed by the NEC, any PV that is load side connected in the main panel is by 705.12 required to be at the opposite end of the bus from the main breaker, the interlock kit, and the generator breaker. I don't know of any interlock kit that would turn off the PV breaker when the source at the other end of the bus is switched from the grid to the generator.

It seems to me that the solution you are proposing depends on someone turning off the PV breaker when/before the source is switched to the generator. That would indeed protect the generator, but I wouldn't design it that way. It is true that the inverter will shut down when the power goes out and before the system is switched to the generator, but if the PV breaker is left ON the inverter will probably start up again while the generator is running and can potentially backfeed it. If the generator produces a clean sinusoidal voltage waveform, the PV system has no way of knowing whether the supply to the bus is from the utility or the generator.
 
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What it comes down to in residential is that this situation is a real pain in the you-know-what if all the branch circuits that the homeowner wants backed up on the generator are in a service panel that's also a meter/main combo with one main breaker. That makes the necessary supply side PV connection a ton of extra work, either by replacing the meter/main or moving all the loads to a sub. Most other situations, such as a separate meter socket, or a main distribution subpanel that's downstream of the service panel, usually will make it much easier to do the PV connection on the supply side of the panelboard that needs the interlock.
 
ggunn said:
The interlock kits I have seen are at the main breaker with the generator breaker at the same end of the bus. The interlock prevents the main breaker and the generator breaker from being ON at the same time, and the kit is just a metal plate attached to the breaker handles.

If your design is governed by the NEC, any PV that is load side connected in the main panel is by 705.12 required to be at the opposite end of the bus from the main breaker, the interlock kit, and the generator breaker. I don't know of any interlock kit that would turn off the PV breaker when the source at the other end of the bus is switched from the grid to the generator.

It seems to me that the solution you are proposing depends on someone turning off the PV breaker when/before the source is switched to the generator. That would indeed protect the generator, but I wouldn't design it that way. It is true that the inverter will shut down when the power goes out and before the system is switched to the generator, but if the PV breaker is left ON the inverter will probably start up again while the generator is running and can potentially backfeed it. If the generator produces a clean sinusoidal voltage waveform, the PV system has no way of knowing whether the supply to the bus is from the utility or the generator.
Click to expand...
Simple solution home owner switch off pv breaker also #7
 
ggunn said:
But of course and as we all know, not everything that is permitted through omission by the NEC is a good idea. :D
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Exactly. NEC 90.2(A):
The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons.
The NEC does not care if someone poofs their backup generator as long as there is no fire or people doing the 60 cycle chicken.
 
ggunn said:
Suit yourself, but I would never depend on the homeowner remembering to turn off the PV breaker when forgetting to do that could have catastrophic consequences to the generator.
Click to expand...
How many such incidents every year?
Any statistics?
 
Deltaforce said:
How many such incidents every year?
Any statistics?
Click to expand...
I would not design a system that relied on the homeowner remembering to turn off the PV manually every time the power went out in order to keep it from destroying the generator just to make it easy on myself, and I would not be afraid to convert the PV from a 705.12 installation to a 705.11 interconnection to protect the generator; I have done so many times and at least here in the US it's not at all a big deal. But as I said, suit yourself; it's your problem to solve, not mine. Peace out.
 
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