I have 200A service but,

I want to add a whole house generator (GENERAC 17k), but my transfer switch is only 100A.

Can I add a 200A subpanel (NEMA 3R 12-space with 200A main) on the outside of the house and then use a 100A dipole breaker to run to the transfer switch? I also plan to install a 30A dipole in the subpanel to run to an outbuilding.

I plan to change my inside load center to 100A and just have 100A service to the house circuits (backed up by generator) It’s a small house with gas appliances and heat and my garage has it’s own 100A service (seperate meter).

Are there any concerns installing the subpanel on the outside of the house, connecting the transfer switch to the 100A breaker and using my inside load center for the generator circuits?

  • You don't need to "change your inside load center to 100A" if I grasp that part correctly. Perfectly fine to feed a 200A panel from a 100A breaker. The 200A breaker will never trip, but still serves as a disconnect, and the 100A feed breaker will trip if loads exceed (reduced) capacity.
    – Ecnerwal
    May 8, 2019 at 11:58

1 Answer 1


Yeah, that's how you do that.

  • A 200A main panel which contains a 100A feeder breaker to
  • A xxxA subpanel
  • via a 100A transfer switch.

The 100A feeder breaker protects the transfer switch.

Assuming the subpanel is quite large (30-space +), it will surely be rated well over 100A. It will be able to operate safely downline from a 100A breaker.

If the subpanel happens to be what is currently the main panel, well that is just fine! Make sure to rigidly, obsessively separate neutral and ground, and remove the N-G bond. There should be infinity ohms between N and G, provided the neutral feed line is pulled.

Loads which you do not want to place on generator go inside the main panel.

The only thing I don't like about your plan is putting the 200A main panel on the outside of the house. Momma taught me not to leave my valuable electrical devices out in the rain. I would make some effort to seek an inside location.

Also, I think buying a 12-space panel is "throwing good money after bad". Nobody ever came onto this forum and said "I am trying to add a circuit and have plenty of spaces in my panel". But we hear the other thing a lot. Therefore I would definitely aim to have at least 45-50 genuine spaces between your main and sub. And double-stuffs (that fit 2 breakers in one space) are no longer a workable way to solve that, since AFCI and/or GFCI are required on so many circuits, and they don't make AFCI/GFCI in double-stuff.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.