Do I need a sub panel


Old 02-24-05, 05:24 PM
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Do I need a sub panel

Just finished a detached garage and have it wired with 12-2 with ground to where I would like to install a sub panel. The new building is about 20 feet from the attached garage where the main panel is located.

I will run a 4 wire cable. 2 hot, one neutral, and ground in PVC underground to the new location.. Copper rod will be grounded near new location.

Where in the main panel can I install this new wiring? I do not have any open slots for a new breaker. And will I need a circuit breaker in the new panel, and what amp rating?

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Old 02-24-05, 05:45 PM
Join Date: Sep 2003
Location: Central New York State
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How many circuits did you run in the garage? How many circuits did you not run in the garage that you may need in the future?

As for the existing panel, you need to free up space. Will the existing panel allow for tandem breakers? If the existing panel won't accept tandem breakers and you are really out of space and can't eliminate two circuits, then you will need a subpanel next to the main panel.
Old 02-24-05, 05:56 PM
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Hey Gabe- I would put a 100 amp panel out on the garage. I would set a 20-24 circuit panel. The reason is they are not a lot more than a 12-16 space so don't be cheap. You can always use the power. The idea for getting power for the sub could come a few ways. 1st is to put in tandem or piggy back breakers in your main panel to free up two slots. The other would be to move two circuits out from the main to the sub so you could use those spaces now for the new sub panel power. You will have to make sure that your pipe is big enough for all the wires you need. I would run a 1 1/2 inch pipe and pull #2s. You could go with a 1 1/4 but I prefer to go BIG. I would use a main breaker panel and would "NOT RUN" a ground out from the main..instead you will drive two rods at least 6' apart and you will bond the sub in this case. " TREAT IT AS A SEPERATE SEVICE " You might have to run your two small circuits in a diff pvc. I can't tell you for sure if in your area you can run the branch feeders with the other branch circuits. Our AHJD would let it go. Putting a main out there will give you the advantage of killing power at the garage if a problem shows up instead of running to the other garage. Remember to use plastic bushings and to protect the #6 ground wire from outside damage....HOPE THIS HELPS

Old 02-24-05, 06:03 PM
Join Date: Sep 2003
Location: Central New York State
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Run the ground out to the panel. Even though it MAY not be required, it is a good idea.

Do not move any house circuits to the garage. That is not a good idea at all. Keep the house circuits in the house at the main panel or a sub right next to it, and keep the garage circuits in the garage.

100 Amps to the garage? Not unless you ever plan on using it out there. Unless I had a need for it, I wouldn't go more than 60 amps.
Old 02-24-05, 06:11 PM
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It will not hurt to move the few circuits out to the garage. 100 amps you bet baby go the distance.."If you wire it- they will come" You should not run the ground out if you are driving new ground rods THAT IS A BAD IDEA! YOU ARE CREATING ALTERNATIVE PATHS TO GROUND AND THAT IS A NO_NO.

Old 02-24-05, 06:34 PM
Join Date: Oct 2004
Location: Orlando, FL
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If the distance is only 20 feet and you only have a few circuits you might just want to pipe the circuits from the main structure.
Old 02-25-05, 04:33 AM
Join Date: Sep 2003
Location: Central New York State
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Running the ground wire to the main panel and and also running ground rods is not wrong. It does not create a problem. In a normal setup you have "alternative paths to ground" already, as you typically also have the incoming water pipe, in addition to the ground rods.

Garou makes the other point I was going to make. If you only need one or two 20 amp circuits in the garage, then simply use 12-3 wire, run a multiwire circuit and be done with it. No subpanel, no muss, no fuss. However, you do need to understand what a multiwire circuit is and how to properly wire it.

By the way, ghow deep do you plan on burying the PVC conduit?
Old 02-25-05, 06:50 AM
Join Date: Sep 2004
Location: NW Ohio
Posts: 188

The advantage of this forum is getting experienced advice from various callings. Responses here have offered you a fair range of solutions per your question. You don't mention the size of your exisitng service or the size of your new building.

If it were me, I would consider this:

What are you going to use the new building for in the immediate and distant future? What is the size of your exisiting electrical service? Is there anything else in the house you may need additional power for in the future?

I would make a tiered plan for the new building from basic/economy on up to all the bells and whistles. After doing a little pricing etc and filtering it through your personal economy, I bet your answer will be right there....
Old 02-25-05, 06:52 AM
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Sorry for the delay in getting back to you experts.. Here is my system.
My main panel has 14 single breakers. 1 Dryer, 1 Range, and 1 Air Cond. breakers.
I think I can buy Dual Circuit breakers, and I understand a dual (tandem) breaker will snap in where one single breaker space is. Which is a 1" of space. Correct?

Buying two -duals will free up two singles and give me the needed circuits for the sub panel. Cotrrect?

Here is the brand name and number on the main panel... Square D Series L7.
#Q0C20MW225, if that means anything.

Here is the set-up in the new garage.

From the area where I want the sub panel, I have a 12-2 wire going to two- wall receptacles on the south wall, and on to a wall switch by a side door on the south wall and up to two- ceiling receptacles for two fluorescent lights. I have repeated this for two other fluorescent ceiling lights, wired the same way and a light switch and two wall receptacles on the west wall..
Also one 12-2 wiring going to two receptales in the ceiling for two garage door openers, and on to two wall receptacles on the east wall.

So I have 6- wall receptacles, four ceiling receptacles for the four lights, and 2 ceiling receptacles for the two garage door openers.
I did this so I could have a circuit breaker for each 12-2 wiring coming from the sub panel...

My guess would be, that I would need a sub panel..

My main concern here, what size cable (amp wise) would I need from the main panel to the sub. And go as 'waterfowelman' says. 20-24 circuit panel-100 amps. Or is that too much?

I will use the 1-1/2' dia. PVC and bury it about 2' down.
Old 02-25-05, 07:48 AM
Join Date: Sep 2000
Location: United States
Posts: 18,497
Here's my advice:
  • Put in a subpanel rated for 100 amps. But run #6 copper wire out there from a 60-amp double-pole breaker. Use tandem breakers to free up space.
  • Use either 6/3 UF-B cable, buried at least 24" deep, or #6 THHN/THWN wires buried at least 18" deep in conduit. If you use the individual conductors, run three plus ground.
  • Install one grounding rod at your garage--two if the inspector tells you to. There is no concern here with alternative paths to ground.
Old 02-25-05, 08:15 AM
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Thanks.. trs4594..

The new garage is 28' x 28'.. It will be used to store the bass boat, a large lawn tractor, and golf cart.. Plus I will have room for my work benches and some power tools, such as table saw, routers, and etc. I think I have installed enough electrical outlets to cover the uses. This will free up my main two car garage..

John Nelson, also thank you for the advice here. I will install the 100 amp sub panel and run the #6 THHN/THWN in the 1-1/2 PVC and down 24" deep. with two- rods as grounds. I will remove two single pole breakers and insert two dual 60 amp breakers.

And thanks to all the others here that gave good ideals. I'm sure they are all worth notice.

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