Idiot proof inverter backfeed ?

[InspectorLance]

I am setting up a solar backup system to backfeed my home during power outages or emergencies. Of course I have to have the main breaker turned off to prevent backfeed to the grid, but is there a switch/relay I could install between my electric panel and my inverter to prevent accidental backfeed voltage damaging my inverter? My system is attached to a subpanel out in my barn. I want to make it idiot proof for the wife and teenage kids to be able to turn on if I am not home. With not being located at the main panel, a typical transfer bar system won’t work. I have seen magnetic relay systems in the past. What is the name of the switch that I need to install between the inverter and my subpanel? Of course there is the breaker in the subpanel connected to the inverter that would need to be switched on/off but I want to have additional safety features to not damage the inverter in case somebody does not follow the directions properly.
Thanks

 

[12VoltInstalls]

That is why you use a transfer switch

That’s also “code”

 

[InspectorLance]

That is why you use a transfer switch

That’s also “code”

Yep, sure is, but how would you go about doing that when the inverter is sending in power from a subpanel hundreds of feet away from the main panel down at the house?

 

[12VoltInstalls]

course there is the breaker in the subpanel connected to the inverter that would need to be switched on/off but I want to have additional safety features to not damage the inverter in case somebody does not follow the directions properly.
Thanks

The transfer switch would uncouple the subpanel; no breakers to switch.

It’s not only simpler- it’s not an additional safety festure- it’s THE safe way of doing it.

The subpanel HAS TO be in the structure it is servicing and be accessible there. The transfer switch would switch from grid entrance panel supplying the subpanel in the house with power from the grid to power supplied by the inverter to the same subpanel in the house.
That is “code” and safe. It is not safe to provide entrance to power not disconnectable from the space it is powering.

 

[InspectorLance]

I have seen auto transfer switches, that operate off of relays. Guess that what I am looking for.

 

[John Frum]

You can also use an interlock kit https://www.amazon.ca/Generator-Interlock-Cover-Frame-Breaker/dp/B08V8FJKLZ

 

[John Frum]

Best way is to use an inverter/charger with an integrated automatic transfer switch.

 

[Zwy]

I am setting up a solar backup system to backfeed my home during power outages or emergencies. Of course I have to have the main breaker turned off to prevent backfeed to the grid, but is there a switch/relay I could install between my electric panel and my inverter to prevent accidental backfeed voltage damaging my inverter? My system is attached to a subpanel out in my barn. I want to make it idiot proof for the wife and teenage kids to be able to turn on if I am not home. With not being located at the main panel, a typical transfer bar system won’t work. I have seen magnetic relay systems in the past. What is the name of the switch that I need to install between the inverter and my subpanel? Of course there is the breaker in the subpanel connected to the inverter that would need to be switched on/off but I want to have additional safety features to not damage the inverter in case somebody does not follow the directions properly.
Thanks

Need more details. The first disconnect device after the meter is the house main panel or the barn? Where is the meter located and does it have a disconnect right at the meter? Your inverter is in the barn or house? What model inverter?

It appears the service entrance with meter is at the house and you want to backfeed power from the barn. There may be code requirements for the subpanel feeding a larger panel related to max amps.

 

[InspectorLance]

You can also use an interlock kit https://www.amazon.ca/Generator-Interlock-Cover-Frame-Breaker/dp/B08V8FJKLZ

That would not work, because this is a subpanel in my barn, and would not cut main power coming into the home.

 

[InspectorLance]

Need more details. The first disconnect device after the meter is the house main panel or the barn? Where is the meter located and does it have a disconnect right at the meter? Your inverter is in the barn or house? What model inverter?

It appears the service entrance with meter is at the house and you want to backfeed power from the barn. There may be code requirements for the subpanel feeding a larger panel related to max amps.

Your last paragraph is correct. Main power from the city comes into the house, and then there is a subpanel in the barn. Solar panel system battery bank and inverter will be in the barn, and backfeed. I am thinking that a automatic transfer switch relay type system would be proper to prevent backfeed situation. I have had similar systems in the past, that I would just flip the appropriate breakers, but I understand how the system works. I was thinking of setting it up so that the wife or teenage kids could flip the switches if I was not home. I need a more idiot proof system in this situation.
Possibly an automatic transfer, a switch between the city power and main panel ? That would be idiot proof and meet basic requirements. Any links to this type of switch? Relay, automatic transfer switch to prevent backfeed.

 

[John Frum]

That would not work, because this is a subpanel in my barn, and would not cut main power coming into the home.

Perhaps I misunderstand your setup.
I meant you put the interlock kit on the service entrance panel.
The interlock makes mains power and power from the back feed breaker(from the barn subpanel) mutually exclusive.
What have I misunderstood?

 

[InspectorLance]

Perhaps I misunderstand your setup.
I meant you put the interlock kit on the service entrance panel.
The interlock makes mains power and power from the back feed breaker(from the barn subpanel) mutually exclusive.
What have I misunderstood?

Maybe I am misunderstanding, but as I understand it, an interlock switch at the main panel that would shut off the main breaker before you could turn on the breaker to the barn would leave my barn with no power during grid power. This is an emergency backup system located in the barn. I can just flip all the breakers as needed, but would like to have a more idiot proof system, and more conforming to regulations. But I am not much for conforming to regulations

 

[John Frum]

Maybe I am misunderstanding, but as I understand it, and interlock switch at the main panel that was shut off the main breaker before you could turn on the breaker to the barn would leave my barn with no power during grid power.

I think what you are saying is when mains power is available you want the barn sub-panel energized from the service entrance panel.
But you want to be able to back feed from the sub panel if mains power is un-available, confirm?

 

[InspectorLance]

I think you may have a typo in your first paragraph, if you mean to say if main power is unavailable, then I want power from the barn sub panel to energize. That would be correct.

 

[Bvillebob]

It's really fairly simple, I'm not sure what the issue is. I have a very similar setup, my solar is all in my barn a couple of hundred feet from the house. I have one run of cable that goes from the house to the shop which was installed before I had the solar, I use it to charge the batteries if they get low and there's no sun. I have another run of cable that runs from the shop to the house. It feeds a Reliance transfer switch next to the main breaker, which has 6 switches to feed 6 circuits in the house, just throw the switch and the circuit is disconnected from the mains and is fed from the solar, easy as can be.

If you try to use one run of wire to both feed power to the shop and feed the house from the shop, then it gets complicated and risky, that's why i invested in the cable to run a second, separate feed from the solar to the house, it makes things much simpler and safer IMHO.

 

[InspectorLance]

With my system I would always want to manually turn on my inverter. Primarily I just want to prevent potential backfeed of main power to my inverter, and of course not be able to backfeed to the grid. I believe there is a electromagnet type relay system for this. What is the name for this type of relay, so I can find it online and order one to install.

 

[12VoltInstalls]

You cannot do what you describe without isolation. Isolation behind a transfer switch allows the grid to be safe from your inverter killing someone and insures off-phase grid doesn’t fuse your inverter guts to the case slightly before the neighbor calls the fire department.

Secondly, as I mentioned previously and two others described, you must have power controlled within the space it is distributed. This is code.

So you have a critical loads panel behind a transfer switch that switches between entrance panel and inverter; you cannot feed the transfer switch directly from grid or inverter into panel without a fail-safe 200A+ disconnect. If you put that in place just remember to throw all the non-critical breakers in entrance panel to ‘off’ before you move transfer source to the inverter do inverter capacity is not exceeded
But you still must be able to disconnect within the structure serviced.

It doesn’t matter if the disconnect is magnetic or fully manual or automatic. It just needs to be impossible for to-grid feedback from your system and vice versa.

 

[John Frum]

I think you may have a typo in your first paragraph, if you mean to say if main power is unavailable, then I want power from the barn sub panel to energize. That would be correct.

Nope I meant available.
2 scenarios...

Mains power available:
Service_entrance_panel->sub_panel

Mains power un-available:
Service_entrance_panel<-sub_panel

Is that what you want to achieve?

 

[acdoctor]

A automatic transfer switch on the service will simply close utility to main panel when utility is present and disconnect utility from main panel when it is not. It is also supposed to close secondary power supply to main panel. ( double pole, double through switch and common is tied to main panel.
Not code but you could use a motor starter ( suitable amperage to handle the utility). Wire to the the utility to main panel and power the stop start buttons from utility. When utility drops and recovers starter won’t close until you push the start button. You would still need to go to the barn and run that breaker on both ends of the cycle. I am not saying it’s code or a good idea and not sure it would solve all your problems but you wouldn’t need to fiddle with the main breaker. May cost more than running more wires to barn like was mentioned before.

 

[Zwy]

Your last paragraph is correct. Main power from the city comes into the house, and then there is a subpanel in the barn. Solar panel system battery bank and inverter will be in the barn, and backfeed. I am thinking that a automatic transfer switch relay type system would be proper to prevent backfeed situation.

You really need a disconnect at the service. A manual disconnect would be fine. It needs to disconnect neutral from grid.

I have had similar systems in the past, that I would just flip the appropriate breakers, but I understand how the system works. I was thinking of setting it up so that the wife or teenage kids could flip the switches if I was not home. I need a more idiot proof system in this situation.
Possibly an automatic transfer, a switch between the city power and main panel ? That would be idiot proof and meet basic requirements. Any links to this type of switch? Relay, automatic transfer switch to prevent backfeed.

Yes, you could install an automatic transfer switch between city power and main panel. A manual switch is easily sourced for higher loads, an automatic will be higher priced. The ATS needs to be the size of your main service panel disconnect. If 200A service, then the disconnect needs to be 200A rated. https://www.google.com/search?q=200...QuMzKYAQCgAQGwAQrIAQi4AQLAAQE&sclient=gws-wiz

I would recommend you hire this done, this would most likely require an inspection.