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matt151617 09-10-2011 08:03 AM

Garage Subpanel
Currently I have 1 12/2 line running into my detached garage. It goes into a subpanel with 2 20amp breakers. 1 of the breakers power the lights and outlets in the garage and the other powers a shed and pool pump. There is also a 12/3 wire running to the exterior garage lights so they can be controlled from inside the house.

What I'd like to do is take the 12/3 for the exterior lights and hook it up to the panel as a new circuit, so the garage outlets are on their own circuit and everything else is on another circuit. Running new line is out of the question as everything is paved over and the original cable is buried. How do I wire up multiple feeder lines into the subpanel?

diyorpay 09-10-2011 08:55 AM

Hmm. Assuming the 12/3 is for 3 way light switches to detached garage exterior lights (1 switch in house, 1 switch in garage). If you rewire, you'll lose that. It is possible that this wiring could be 15 Amp light stuff adequate for lighting and other light duty.

Use 1 of 2 'new' wire runs (black and white for one, red and white for the other) for exterior garage lights but with a regular 2 way light switch from house (1 switch in house, no switch in garage). That leaves 1 'new' circuit to garage tapped off from the switch box in your house. Don't take to garage subpanel. Rewire to old switches and lights in garage, freeing up 1 20 amp circuit in subpanel. The switchbox in your house is the 'subpanel' for garage lights and outlets.

That frees up the 1 of the 2 20 amp breakers in garage subpanel.

matt151617 09-10-2011 09:13 AM

I don't care about loosing the switch in the house, just the one in the garage, since I'm going to put a motion sensor on it. I forgot to mention I planned on keeping the red wire free for eventually hooking up an interconnected smoke detector. The wiring is definitely all 12 gauge, UF coming in and spliced into NM.

So I suppose I could wire the old switch wiring directly to the outlets but it's definitely against code if it doesn't run through a subpanel. The current setup needs rewiring anyways (switched neutrals, etc).

Are there subpanels that allow multiple feeders? Or should I just pull the whole subpanel and install a service disconnect?

J. V. 09-10-2011 11:24 AM

A 12/2 line (branch circuit) is not allowed for any 220 volts, so you only have a 120 volt panel. Is it wired for 120 or 220? If it is wired for 220, it is wrong. What type of wire is buried. They should have pulled a 12/3 cable out there. You are very limited with the 12/2 cable. You need a disconnect out there too.

matt151617 09-10-2011 12:10 PM

There is no 220, just 120. The lights have 12/3, the outlets and everything else have 12/2. So there's one 12/3 and one 12/2 buried. The 12/3 gets it's power off of the 12/2 going into the subpanel.

I guess I'll just install a service disconnect for both lines, either 2 separate ones or 1 if it can handle 2 separate circuits. If a breaker trips I'll just have to go into the basement and reset it there.

matt151617 09-13-2011 07:17 PM

I've researched this a lot and read some books, and it's not really clear. Can I take the 2 separate 12 gauge lines and combine them together into the entry of the subpanel? Then split it? Or do I need to install 2 separate disconnect boxes?

Jim Port 09-13-2011 08:50 PM

You are feeding the shed with a single circuit. You do not need a disconnect.

You are also severely limited by only having 20 amps to work with.

matt151617 09-13-2011 09:17 PM


Originally Posted by Jim Port (Post 727668)
You are feeding the shed with a single circuit. You do not need a disconnect.

You are also severely limited by only having 20 amps to work with.

Understood. I'm just figuring how to wire up a new 20 amp circuit for the outlets. There's currently a separate line powering everything; I want that line to only power the lights, etc, and the new 20 amp line to power the outlets. Is there a way to run both these lines through the subpanel?

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