Generator/Inverter Interlock

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Do they make an Interlock for a single pole breaker? I have a customer wanting to connect their parallel Honda gen sets to the panel. The problem is, for one, it is only 120V, and two, it would be hard to choose what to run since only half the bus would be energized.
I think the better choice would be to use either a manual switch with a few breakers or just a panel for the desired circuits. Either way, I would need some type of Interlock for the main.
 

Buck Parrish

Senior Member
Location
NC & IN
I don't see how that would prevent any back feed except to the breaker that was turned off.
You're right it would need to be and snap to the main breaker in a panel or small sub panel, I use them when building a generator panel used with a 100A 2 pole breaker above than the 2 pole 30 ( from generator) directly below.
. It works similar to a on up or on down switch. Except it snaps on the breaker. I use a little epoxy to assure it stays tight.
I thought that's what you were wanting to do cut power to the breaker that is turned off. Than vice a versa
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
You're right it would need to be and snap to the main breaker in a panel or small sub panel, I use them when building a generator panel used with a 100A 2 pole breaker above than the 2 pole 30 ( from generator) directly below.
. It works similar to a on up or on down switch. Except it snaps on the breaker. I use a little epoxy to assure it stays tight.
I thought that's what you were wanting to do cut power to the breaker that is turned off. Than vice a versa
Somehow I'm not picturing what you're saying about building a gen panel. Help my fuzzy mind out on this.😕
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Does the customer have any MWBCs? There could be a problem overloading the neutral if both sides were fed with the 120V generator.
Just something to keep in mind.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
Does the customer have any MWBCs? There could be a problem overloading the neutral if both sides were fed with the 120V generator.
Just something to keep in mind.
I have no idea about MWBC as I haven't been to look at it yet. Just been communicating via phone/texts. I haven't decided how I'm going to do this yet. If I feed the main panel, I won't feed but one bus. Then I would have to either move the circuits from the unpowered side to the one that is. With only a 30A possible load I don't see having to move much.

If they want to not have to turn off 2-pole breakers and hunt/choose what single poles to power, I would run a subpanel just for gen power with only the loads they for sure want.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
I have no idea about MWBC as I haven't been to look at it yet. Just been communicating via phone/texts. I haven't decided how I'm going to do this yet. If I feed the main panel, I won't feed but one bus. Then I would have to either move the circuits from the unpowered side to the one that is. With only a 30A possible load I don't see having to move much.

If they want to not have to turn off 2-pole breakers and hunt/choose what single poles to power, I would run a subpanel just for gen power with only the loads they for sure want.
Why would you have to turn off 2 pole breakers?
 

Buck Parrish

Senior Member
Location
NC & IN
Somehow I'm not picturing what you're saying about building a gen panel. Help my fuzzy mind out on this.😕
It's just a little clip that looks like a lockout that snaps on a breaker. But it has a piece of metal that swivels. So when you put one breaker one way the adjacent breaker must be the other.
I've never used one with a single pole breaker. But it does snap to just one side of the two pole. So it should clip on it.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Standard interlock kit with a two pole generator breaker just jumpered. 120 volt inlet prevents a 120/240 volt generator from being connected. As others have said, MWBC’s would be the only concern, but a majority of houses do not have them.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Standard interlock kit with a two pole generator breaker just jumpered. 120 volt inlet prevents a 120/240 volt generator from being connected. As others have said, MWBC’s would be the only concern, but a majority of houses do not have them.
Every house I wired prior to expanded use of AFCI's had MWBC. Even so with that small of generator you are not likely to overload any circuit conductor. You would knowingly have to try.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Every house I wired prior to expanded use of AFCI's had MWBC. Even so with that small of generator you are not likely to overload any circuit conductor. You would knowingly have to try.
I agree, the only one I know of around me, is my mom and dad’s house that I wired back in the early 80’s. (First house I ever wired) Used them in the kitchen. I haven’t seen any in Atlanta. Even prior to AFCI.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
If they want to not have to turn off 2-pole breakers and hunt/choose what single poles to power, I would run a subpanel just for gen power with only the loads they for sure want.
Why would you have to turn off 2 pole breakers?
The L1-L2 loads and the L1-N loads on the bus that is not being fed by the 120V generator will be in series with each other, and therefore draw current from the L2 bus that the generator is supplying. So either the 2 poles and/or the L1-N single pole breakers need to be turned off.
 

Todd0x1

Senior Member
Location
CA
What would get rid of the problem is installing a 120->240/120 transformer. 120v from the generators and 120/240 into the panel interlock. I dont know if the little honda inverter generators would be able to magnetize the transformer before tripping on overload.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
The L1-L2 loads and the L1-N loads on the bus that is not being fed by the 120V generator will be in series with each other, and therefore draw current from the L2 bus that the generator is supplying. So either the 2 poles and/or the L1-N single pole breakers need to be turned off.
Supply both busses with the 120 volt while on generator.
 
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