Building Garage and upgrading service

[nebben]

I'm still in the planning phase, so please bear with me here.

Right now in our 1946 house, we've got 100 amp electrical service that goes over an aerial. Since we want to build a non-attached garage, we will be increasing the electrical demands beyond what the house panel can provide. I plan to talk with a city inspector and get a local electrician onboard, but just for general planning purposes I'm prodding your brains.

Given: I want our service from the utility to be upgraded to 200amp. I want to move all wires underground.

Option #1: run new 200amp service from utility to the house. Because the existing panel is 100amp, it would need to be replaced with a 200 amp unit and all breakers reinstalled (or replaced?). Panel will be wired to 100 amp feed that goes to the garage subpanel.

Option #2: run new 200 amp service to garage (which will be all new construction and a new panel or subpanel anyway). Panel will be wired to 100 amp feed that goes to the existing 100 amp house panel. In effect, the house's panel which currently has the 100amp utility service entrace would turn into a subpanel.

So given these two options, with all other things being equal, I prefer the second option for several reasons. I wouldn't need to replace the house's panel and it would require less materials since the garage would be located between the utility pole and the house. Additionally, the current panel is mounted in an exterior wall with intricate stonework around it- I don't want to mess with that if I can help it! For option 1, if I'll be changing the current house panel from 100 to 200 amp, would I need to bring up existing wiring in the house to current code at the same time, or would this largely just be a simple replacement of the panel? For option 2, by changing the house from a main to a subpanel, would I need to bring up existing house wiring up to current codes too...or add additional grounds and such?

Thanks fellas!

[nathank]

I just went through this exact scenario. I chose to install service on my new building and subfeed the house. It was easier / less materials.

[Torque1st]

The subpanel in your house would have to be converted to a 4 wire panel with an isolated neutral.

I am doing something similar to #1 with an attached garage. The main house panel is going to 200A and a 4-wire subpanel is being installed in the garage. The main house panel is just barely adequate to serve the existing home and all the breaker slots are full.

[timgr]

My garage is set up like scenario #1. My existing house service was 100A, upgraded to a 200A service and a new panel. The garage uses a 4-wire subpanel, actually the 100A panel that was originally in the house (the electrician said it was fine, so I saved a few bucks). The new service is overhead though, as was the original service. The garage is fed underground.

I think you're no better off with option #2, for the reason that Torque1st wrote ... unless the ground and neutral can be isolated in your existing panel.

[nebben]

So from the sounds of it with either scenario, if the house panel becomes a subpanel or is replaced, it will need to be upgraded to a four wire setup?

[sberry]

4 wires between panels.

[timgr]

IIRC some panels can be configured for main/sub panel use by keeping/removing a shorting bar that grounds the neutral buss. If so, you can remove the bar in your house panel and connect your four wires from the main panel at the garage. If not, you'll need to replace the panel.

[Torque1st]

Main service entrance panels are 3-wire with a common (connected) neutral and ground bus. Subpanels fed from the main panel have an isolated neutral not connected to the subpanel enclosure and a subpanel also has a ground bus connected to the enclosure.

[nebben]

Good timing on this thread I guess? I just read the page listed in the other thread right now (100 amp feed to detached garage) and found this link: http://www.selfhelpandmore.com/home-wiring-usa/accessory-structures-to-dwellings/wiring-a-detached-garage-2002.php. That clears up the reasoning for the 4 wire stuff. Thanks for the good info today fellas!

[Torque1st]

Search is good... :)

[Stuart in MN]

You haven't mentioned the age or brand of the existing panel in the house, or what condition it or the existing house wiring is in....if they're in good shape putting the main service in the garage may be the way to go, if they're in tough shape this would be the time to fix them.

[trainer]

I did option # 2 when i built my garage. To upgrade in the house to 200 amps would have involved bringing the entire house up to current code. The 100 amp panel in the house is in good shape with some spaces available, so we left it alone.
I had the cable from the garage feeding the house run underground, and was able to eliminate an overhead wire above the driveway as well as the ugly meter on the side of the house.

Now my garage has all the power I'll ever need.

It was the cheapest option for me as well.