detached building on same service

[difowler1]

Using a branch circuit, I have ran power to a sub panel for a detached garage many times.

I have never supplied power to a sub panel for a guest house. I also haven't provided power to a guest house from one of the (main house) 2ea 200amp panel boxes on a 320amp service.

The main house has an existing 320amp service. The customer wants to supply power to his guest house from the main house. The main house and the guest house have all gas appliances. I still need to do the load calculation, but supposing the load was under 320amp for both houses, can you run a house from a branch circuit (240volt, with neutral and ground)? If so, what is the largest size breaker you can install in a 200amp panel as a main breaker for the guest house?

 

[augie47]

If I may, in order to improve discussion, please note the NEC definition of branch circuit as the circuit from the Final OCP to the outlet(s). Your power from your main residence to your guest house would be a feeder or even possibly a service depending on how to install the job.
As long as the load calculations allow, you can install a 240/120 volt 4 wire feeder to the guest house from either of the main house panels. The breaker size may vary depending on the manufacturer, but a 125 amp should be available in all makes.
Unless prohibited by local Codes, you are also allowed to install a service to the guest house directly from the 320 amp meter.

 

[difowler1]

detached building on same service

Sorry, wasn't thinkin, "feeder"

If I may, in order to improve discussion, please note the NEC definition of branch circuit as the circuit from the Final OCP to the outlet(s). Your power from your main residence to your guest house would be a feeder or even possibly a service depending on how to install the job.
As long as the load calculations allow, you can install a 240/120 volt 4 wire feeder to the guest house from either of the main house panels. The breaker size may vary depending on the manufacturer, but a 125 amp should be available in all makes.
Unless prohibited by local Codes, you are also allowed to install a service to the guest house directly from the 320 amp meter.

 

[LEO2854]

Using a branch circuit, I have ran power to a sub panel for a detached garage many times.

I have never supplied power to a sub panel for a guest house. I also haven't provided power to a guest house from one of the (main house) 2ea 200amp panel boxes on a 320amp service.

The main house has an existing 320amp service. The customer wants to supply power to his guest house from the main house. The main house and the guest house have all gas appliances. I still need to do the load calculation, but supposing the load was under 320amp for both houses, can you run a house from a branch circuit (240volt, with neutral and ground)? If so, what is the largest size breaker you can install in a 200amp panel as a main breaker for the guest house?

You could come right out of the meter socket and use a main breaker panel guest house.

How big of a load will be in there?

 

[renosteinke]

As I see it, there's no debate: treat the guest house panel as a 'sub.' 4 wires from your main panel, disconnect on the outside of the cottage, ground rods at the cottage. Keep the neutrals and grounds separate.

After all, a 'feeder' is just like a branch circuit, except there's a breaker at the end, instead of an outlet.

The listing of the main panel - look to those stickers in the panel with the tiny upside-down print - will determine the largest breaker you can use. As an example, the 100-A main panel on my house is limited to 80-A breakers. If you can't find the sticker, look to the manufacturers' web site.

 

[kwired]

Some manufacturers have 200 amp breakers available. They will likely take up 4 pole spaces, and may only be listed for installation in specific panels and not just any panel. There are also plug on "sub feed" lug kits for many and will also likely require 4 pole spaces for 200 amps.

If load is less than 320 you will likely find it easier and less cost to just come directly from meter or a J box at/near the meter and install the feed to the guest house as a service, instead of a feeder.