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Old 06-21-2011, 04:14 AM   #1
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Garage sub panel


Hey folks, this is my first post in here, hope you can give me some info! I'm far, far from being an expert but I've already fixed several dangerous wiring situations I've found that the previous owner of my house left for me!

I'm trying to clean up the wiring to my garage, what I have is a 120 line/15 amp breaker, a 120 line/20 amp breaker, and a 240 line/40 amp breaker. All breakers are in the main panel in basement of house, garage is semi-detached (has a fully walled/roofed breezeway between it and the house).

My question is about the 240 line: What I would like to do is take the 240 and put it into a sub panel (it's a 4 wire line with ground). I would like to keep a 40 amp breaker in there for when I want to use it for a welder or whatever but I'd also like to run 2 20-amp 120 lines to gain some more outlets in the garage.

Make sense so far? lol

What I'm thinking is that I can run the 240 line into a disconnect then a sub panel with a 40 amp breaker for a 240 outlet, and 2-20 amp breakers for 120 outlets. Am I way off base?

I'd appreciate your feedback as to whether this is possible or not.
Keep in mind that the 240 outlet would never be used at the same time as the other 2 outlets (and even if they were they should trip the 40 amp in the main panel, right?)

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Old 06-21-2011, 05:56 AM   #2
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Garage sub panel


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I am no electrician by any means. My first thought was that since 240 looks like this "120-0-120" that you could just figure out the neutral and complete the circuit. My guess though is it is not up to code which is going to give you problems later. And If its not up to code it means that it is probably not safe. I would be very careful.

Read this: http://newsgroups.derkeiler.com/Arch.../msg05937.html

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Old 06-21-2011, 07:51 AM   #3
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Quote:
What I would like to do is take the 240 and put it into a sub panel (it's a 4 wire line with ground)
Or is it three wires with ground?

Quote:
What I'm thinking is that I can run the 240 line into a disconnect then a sub panel with a 40 amp breaker for a 240 outlet, and 2-20 amp breakers for 120 outlets. Am I way off base?
Why the disconnect? The sub, if needed, could have its own disconnect.

Are the two 120 circuits dedicated to this garage? If so the 15 amp could provide lighting and the 20 could support several GFCI protected receptacles. This would leave the 240 volt line available for what ever you need 240 for - a welder?

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Old 06-21-2011, 07:52 AM   #4
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Garage sub panel


As he said, he is no electrician...........

Not sure I understand??? You have 3 circuits run to the garage from the main panel in the house???? AND/Or...you want 3 circuits in the garage with one subpanel in the garage?? Ideally the subpanel should be fed with one 240V circuit, 4 wire + gnd. Wire size depends on the size of the subpanel main breaker. From the subpanel, you can run 240 or 120 circuits as you like.

Neutral and ground in the subpanel are to be separated. Separate busses for each, with neutral floating, not connected to the box or ground. At least one ground rod is usually required for the ground conductor.
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Old 06-21-2011, 08:52 AM   #5
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Since the garage is attached, you do not need any ground rods. If the existing 40 amp 240 volt circuit has 4 conductors (2 hots, a neutral and a ground) and the wire size is #8 AWG copper or larger, you can install a subpanel. You do not need a disconnect. You will need a separate ground and neutral bar.
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Old 06-21-2011, 08:57 AM   #6
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lol, sorry guys, I'll try and answer all of you: Yes I want 2 EXTRA 120 lines. Reason is that the one 20 amp I already have is dedicated to my compressor, the 15 amp runs the lights and garage opener. I effectively have no heavy-use outlets to use unless I unplug my compressor. One of the issues I already fixed was that the previous owner had a whole wall of 20-amp "outlets" run off of that 20-amp breaker, problem was that after the outlet my compressor is at, he used 14/2 wire! There were already burn points behind one of the work benches from where it was overheating, I disconnected them all of course, but that eliminated ALL my extra outlets. Plus my compressor really needs a dedicated 20-amp line of its own so don't really want to re-run with 12/2 wire, I'd rather have a new source to run from.

Also, yes this is all fed off the house's main panel, including the 240 line, I just wanted to put a sub panel in the garage to split it up there so I don't have to run any cable into the garage (very difficult to do, no good place to run cable, previous owner ran these 3 lines very..um...half-assed shall we say? )

As for the wire, I actually haven't looked (will tonight) but it's either 8/3 or 8/4 I think. Outlet has 4 prongs.

Lastly, I guess I didn't realize the sub could have it's own disconnect but thinking about it your right a7, I have seen that before so I shouln't need one separately.

That was a question I had, the 240 can't be used to ground the whole system? I'll need a separate ground sunk?

Hope that gave you some info you needed! Thanks guys!!
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Old 06-21-2011, 09:04 AM   #7
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Originally Posted by rjniles View Post
Since the garage is attached, you do not need any ground rods. If the existing 40 amp 240 volt circuit has 4 conductors (2 hots, a neutral and a ground) and the wire size is #8 AWG copper or larger, you can install a subpanel. You do not need a disconnect. You will need a separate ground and neutral bar.
Ha! Took me so long to type up my last post that you got yours in first! Thanks rjniles!! You answered a couple good questions for me! I was hoping I wouldn't need to drop a ground.

BTW, all of this will be done in the not-near-future, I want to totally rewire inside the garage first, he used a mix of all kinds of weird romex, he's got 12/2, 14/2, 14/4 all inter-connected and very redundant, I'd say he ran 100'+ more than is needed to wire it correctly. Not to mention he used beefy metal staples without insulation that are pinching the sheathing HARD!
Only thing I've fixed was the 20-amp line, it's 12/2 from the main panel to the compressor's outlet, the rest at least is all on the 15 amp breaker so doesn't really matter what wire he used, just looks crappy.
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Old 06-28-2011, 05:35 AM   #8
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Hey guys, stupid question here but I need help identifying what type of 240v cable I have coming into my garage, I took a look and can't find any markings on the accessible parts of the cable, only lettering I found was listing the 600v max etc.

I've never worked with cable this big so I'm not sure what I have exactly. It's two black lines and one line of heavy braided wire, is that a neutral or a ground? These are all #6 gauge btw. Not sure if this is 6/2 or 6/3?

Is this usable for my sub panel or will it require even more work? Lastly if this will work for my panel, what's the max breaker I can safely run it off of? Currently has a 40 amp. About 50ft. or so of run length from the main panel in basement. (attached garage).

Thanks guys!!
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Old 06-28-2011, 07:11 AM   #9
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It sounds like you are describing SE 6-2 with ground. It only has 3 conductors and is not useable for sub panel feeders. You need 4 conductors.
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Old 06-28-2011, 07:28 AM   #10
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The fat cable with two inner conductors and a braided metal sheath can be used here only for a 240 only volt circuit. You can run it to a subpanel with only double wide double breakers for such things as compressor, water heater, 240 volt only receptacles.

Since the garage is not (fully) detached, you can run additional 12-2 cables as needed from the panel for additional 120 volt circuits.
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Last edited by AllanJ; 06-28-2011 at 07:31 AM.
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Old 06-28-2011, 07:34 AM   #11
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Originally Posted by AllanJ View Post
The fat cable with two inner conductors and a braided metal sheath can be used only for a 240 only volt circuit. You can run it to a subpanel with only double wide double breakers for such things as compressor, water heater, 240 volt only receptacles.
Allan,

Are you suggesting creating a 240 only sub panel--2 hots and a ground and no neutral. What would stop someone from taking a 120 circuit off that panel using a hot and the ground (for a neutral). Basically it would be an old 3 wire installation. It would not fly with an inspector.
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Old 06-28-2011, 02:56 PM   #12
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Originally Posted by rjniles View Post
It sounds like you are describing SE 6-2 with ground. It only has 3 conductors and is not useable for sub panel feeders. You need 4 conductors.
Okay, thanks for the info guys, that's what I was afraid of when I realized it wasn't a 4-wire line. I'm just going to leave it as a 240 outlet then, I'm going to move it and secure the wire (right now it's just laying loose accross the rafters). I still have two 20A lines coming in so I think I can make do for now.
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Old 06-28-2011, 06:04 PM   #13
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Maybe use the existing 3 wire cable to pull a 4 wire cable - then do the subpanel as described.
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Old 06-29-2011, 01:29 AM   #14
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Maybe use the existing 3 wire cable to pull a 4 wire cable - then do the subpanel as described.
Let's just say running cable intra-structure isn't a strong suit of mine.
Open studs in a garage, that I can handle, but not inside walls, etc. I can't ever get anything to pull.

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