I originally had a contractor increase my residential electrical service from 200A to 400A in anticipation of building out a woodworking shop in my basement. In addition to the original 200A main panel a 200A Breaker box was placed adjacent to the original main. Due to a potential relocation to a new home, I now plan to fitout the basement for a rec room, bathroom, and general storage area. As a result I certainly do not need a 200A subpanel in the basement.

My questions are can I run wire sized to feed a 100A subpanel from the 200A breaker; or, do I need to change the size of the main breaker to match the subpanel? Also, can a Romex type service wire be used; or, do I need THHN type in conduit?

 

You should be able to install a two pole 100 amp breaker in the panel to feed the subpanel. No need to remove the 200 amp main.

Unless subject to damage or local prohibitions you should be able to run SER cable to the subpanel.

 

With a new second 200 amp panel, why do you need a 100 amp subpanel?

 

Thanks for the rapid response pcboss! Unfortunately, this is actually a 200A Service Disconnect and there is no bus to install a 2 pole 100A breaker. It appears I would have to change the 200A breaker to a 100A breaker; and, since it is directly fed from the meter can I would need a contractor to pull the meter, change the breaker, and have a new seal installed on the meter.
This also may be a problem since the service feed is 4/0 Aluminum and I am sure that will not fit in a 100A breaker. Am I correct? I can provide images of the panel if necessary.

Also, I have to run about 65 feet from my breaker location (garage) down to the basement where I plan to locate the 100 subpanel. I am thinking I would need 3 -#2 THHN copper wires and 1- #2 THHN copper ground wires in conduit. Can the conduit be PVC? I would appreciate your guidance on this! Thanks for your time.

 

Sorry I was not clear that it is a single breaker service disconnect and it will be used to feed a subpanel in my basement.

 

I am not understanding your setup. Do you have two disconnects that feed panels inside the house and one of these does not contain any circuits?

 

Sorry pcboss. When we upgraded the service to 400A I was informed I needed to have one location to shutdown all the electrical circuits in the house. Since the existing 200A panel was in the garage, I added a 200A single breaker box adjacent to the existing 200A panel that fed all of the circuits in the house. It was my intention then to install a 200A subpanel in the basement to power the complete basement woodworking shop and feed it from the single 200A breaker in the garage.

 

OK, so it sounds like you have a 200 amp disconnect sitting there that does not feed anything. The 200 amp can be changed to a 100 amp. A 100 amp rated 4 wire feeder can now be run from the disconnect to a subpanel.

 

Thanks pcboss! Have a great day.

 

That's about right.....IF you change the 200 amp breaker to a 100 amp breaker. Rather than do that, I think I'd install a 200 amp rated main lug only panel (MLO) adjacent to the 200 amp breaker disconnect and then install a 100 amp breaker in that panel. The 100 amp breaker can now feed the basement subpanel without the ordeal of having a contractor pull the meter and then having to get the meter resealed.

You don't need #2 THHN conductors. I would use #3s, but the NEC allows you to use #4s for a residential 100 amp feeder (I still would use #3s). The ground should be a green #8 THHN conductor. Yes, you can use PVC conduit; I'd use 1 1/4" conduit.

 

Thanks casual Joe - I appreciate your guidance. That will certainly be better. Have a great day!

 

I hope you understood to feed the 200 amp MLO panel from the 200 amp main breaker disconnect with 2/0 copper THHN. I didn't specifically state that and was just rereading what I had told you and hoped you understood, it didn't seem clear to me as I reread it. The feeder to the MLO panel is allowed to be 2/0 copper in a residence, but a fully rated feeder would have to be 3/0 copper (like you'd use on a commercial job).

 

Thanks casual Joe - yes I understand. The 200A main is actually fed from the meter can with 4/0 aluminum. I will use the 3/0 copper between the main and the MLO panel. I realized your wire size guidance was referring to the run from the 100A breaker to the basement subpanel.