Is there any known issues with supplying 2 panels from one portable generator using interlock kits in both panels? Would be a 30 amp breaker in both panels with interlock kits and both sets of conductors connected to a 30 amp inlet box. Read a brief article where someone said that shouldn't be done as there could be neutral problems. He didn't state what the neutral problems may be but was just wondering if I'm missing something.
Interlock with 2 panels
- Thread starter frofro19
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brantmacga
Señor Member
- Location
- Georgia
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- Former Child
No issue in that setup.
Neutral issues could be if the generator has a bonded neutral & gfci, it’ll trip.
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Neutral issues could be if the generator has a bonded neutral & gfci, it’ll trip.
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jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
The only potential fluky issue I see is if there's any improper parallel connection between circuits in the two panels. Like, two hots from different breakers in different panels connected to the same load. The sort of thing I've seen a couple times in buildings with multiple generations of old and sketchy wiring.
If there were a fluke like that then you risk connecting the generator to the grid if one interlock is switched over and the other is not.
Just something to think about checking first if you have any reason to doubt the quality of the building wiring.
If there were a fluke like that then you risk connecting the generator to the grid if one interlock is switched over and the other is not.
Just something to think about checking first if you have any reason to doubt the quality of the building wiring.
letgomywago
Senior Member
- Location
- Washington state and Oregon coast
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- residential electrician
That should be a quick test though. Throw off one main at a time and check the bus bar with all the breakers on other than the main.
synchro
Senior Member
- Location
- Chicago, IL
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- EE
I think it would be better to have an inlet for each panel. With one generator you'd need to split into two input cables using an external junction box or other means.
The reason I mention this is that with one inlet feeding both panels, you will be joining the neutral bars of both panels together even when the generator is not being used. And probably with 10 AWG wire. It will still work, but there will be some adverse current flow, most importantly when the POCO is supplying power. And I'm sure this will be an NEC violation in the installation.
Joining the neutrals of two input cables will not be part of the installation. And in any case it will only be subject to a limited current if the cables are only connected when using the generator.
Also, two inlets will allow two generators to be used if/when available.
The reason I mention this is that with one inlet feeding both panels, you will be joining the neutral bars of both panels together even when the generator is not being used. And probably with 10 AWG wire. It will still work, but there will be some adverse current flow, most importantly when the POCO is supplying power. And I'm sure this will be an NEC violation in the installation.
Joining the neutrals of two input cables will not be part of the installation. And in any case it will only be subject to a limited current if the cables are only connected when using the generator.
Also, two inlets will allow two generators to be used if/when available.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
I've done it, telling them to always switch both panels over before starting and plugging in the genny.
The combined neutrals will effectively form a parallel between the two neutral buses, like two GECs do.
The combined neutrals will effectively form a parallel between the two neutral buses, like two GECs do.
Jpflex
Electrician big leagues
- Location
- Victorville
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- Electrician commercial and residential
What is poco?
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I would think he's referring to the power company.
Wouldn't the exact same thing be going on with (2) (200 amp) ATS feeding (2) panels being feed from a Generac 22 KW generator? The neutrals are not being switched in that case as well. I don't believe most homeowners would be willing to buy (2) portable generators IMO.
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
In that case, you are paralleling the neutral bars of 2 panels with much larger conductors than when wiring a common inlet to a portable generator (which might use 10 AWG for example). And so if a connection feeding a neutral bar gets compromised, more current may flow through the 10 AWG than it's rated for (it would depend on the resistance through the intervening equipment ground).
While your scenario is possible, is it something that would require a different installation? Many things can go disastrously wrong if you loose a neutral.
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
What makes me sensitive to this issue is that I'm aware of a bus that burned up because a smaller ground jumper had to take all of the load of the electric HVAC when the main one intended for the load got loose. This was a DC application, but the same principles apply.
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Oh. I should mentioned that the bus that burned up was not in a panel, but had wheels on it.
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