Portable Generator with Two Panels

M

MotoDan

Member
Location
Missouri
Occupation
Electrical Engineer
Hello All,

I want to connect my portable generator to my home which has two Square D "QO" panels - the main panel is 200A with a second 100A add on (aux) panel. Both panels have built-in main breakers, are located next to each other and are individually connected to the service entrance. The service entrance is located about 6ft to the right of the panels. I only want to feed the 200A panel from the 12kW generator via a 50A breaker where I will selectively manage which loads I need during a power outage. I don't need an ATS since I plan on starting the generator and doing the switchover manually. I was hoping to use a mechanical interlock on the 200A panel, but am not sure how to best safely (and legally) disconnect the aux 100A panel. I have a 200A ATS that was bought years ago when I was originally considering going with a fixed whole house solution. I wired the entire house when I built it 30 yrs ago under a homeowner test/permit so am familiar with all of the wiring.

I will attach a photo once I have that option (this is my first post).
Thanks for your help!
 
MotoDan said:
Both panels have built-in main breakers, are located next to each other and are individually connected to the service entrance.
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If you only connect to the 200 amp panel and use proper transfer/interlock method there should be no way to supply the 100 amp panel if supplied like you said.
 
kwired said:
If you only connect to the 200 amp panel and use proper transfer/interlock method there should be no way to supply the 100 amp panel if supplied like you said.
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Maybe I misunderstood, do you want to supply both panels with the generator? If so something like Larry posted is likely available from the site he linked to. You will need two open spaces for a breaker from the generator and technically that breaker needs some sort of hold down device if you want full code compliance, many those kits I've seen come with what is essentially a cable tie to use as the hold down. The idea being if a back fed breaker comes unplugged while energized you possibly have hot bus connectors that can contact something undesirable. Reality is the interlock isn't even in place if the panel cover isn't installed and if panel cover is installed the breaker isn't coming unplugged, so take that for whatever it is worth to you.
 
kwired said:
If you only connect to the 200 amp panel and use proper transfer/interlock method there should be no way to supply the 100 amp panel if supplied like you said.
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I'm not sure I understand how the 100A panel doesn't also need to be disconnected. It shares the same feed (paralled wiring) as the 200A panel. If I lockout the 200A panel and backfeed it through the interlocked 50A breaker I would still be backfeeding the service entrance - unless I also disconnect the 100A panel. What I'm looking for is a simple way to disconnect the 100A breaker since its not mechanically tied to the 200A breaker.
 
If one panel's main breaker is turned off, which is required to turn the generator breaker on, that panel is then isolated from everything else, including the other panel.
 
I think he is saying he has two service disconnects off his meter a 100A and a 200A, and in the case of a 12kW generator I'd just move the loads to be backed up to one of the panels as thats not very much load.
 
MotoDan said:
I'm not sure I understand how the 100A panel doesn't also need to be disconnected. It shares the same feed (paralled wiring) as the 200A panel.
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Because:
MotoDan said:
Both panels have built-in main breakers, . . . and are individually connected to the service entrance.

I only want to feed the 200A panel . . .

I was hoping to use a mechanical interlock on the 200A panel, but am not sure how to best safely (and legally) disconnect the aux 100A panel.
Click to expand...
When the 200a panel's interlock is flipped, that panel is then isolated from everything else, including the 100a panel.
 
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