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Old 08-01-2012, 07:11 PM   #1
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Subpanel to outdoor workshop


Hi folks,
I'm designing an outdoor workshop and will be installing a subpanel for some 15A and 20A circuits. Will run a table saw, compressor, lights, drill press, TV/radio, computer, plug in heater. Shop will be 11' x 15'.

My home has the meter with a 100A disconnect outside the garage wall. A 125A subpanel is in the garage about 15' from the main disconnect. My service wires from the main disconnect to the garage sub are aluminum. I can't tell what gauge the SE wires are as there are no markings, they look like #4.

I'm having a gas line installed to my kitchen so the electric range/oven will be replaced with a new gas appliance. I would like to use the 240V circuit, that presently feeds the electric range/oven, for my subpanel in the new workshop. The 240V receptacle is on a wall that is closest to my outdoor workshop. So, where the kitchen 240V receptacle is now, I'd run 1 1/4" PVC, LB at exterior wall, then underground 18" approx 25' to the workshop subpanel. Will be doing a UFER ground in the workshop slab. Will run 4 wires to the workshop subpanel, 2 hots, 1 neutral, 1 ground. THWN conductors or UF in PVC.

It looks like the existing range circuit is #6 aluminum, 2 hots, 1 neutral, 1 ground with a 50A breaker. I don't plan on changing the 50A breaker.

My questions are:

1. Size of subpanel in workshop? 100A?

2. Wire size from kitchen J-box to workshop subpanel using copper? #8?

3. Splicing aluminum to copper? Split bolts and tape? Ideal purples? Other?

4. Any other concerns with this plan?

Thanks for your advice.


Last edited by RM575; 08-01-2012 at 07:19 PM. Reason: Better title.
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Old 08-01-2012, 07:54 PM   #2
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Subpanel to outdoor workshop


if you plan to use the 50amp breaker to supply the new sub, you will only get 50amp service to it.
you can use a 100amp panel off the 50amp breaker.

i dont think it's recommended to splice AL to Copper.

if it were me, i would run all new 2/2/2/4 AL from a 90amp breaker to the workshop.
especially if you're gonna use heavy equipment such as a compressor and saws.
you could also opt for a smaller copper sub panel, but they are pricey.

the other guys may have better input on this one

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Old 08-01-2012, 08:05 PM   #3
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Subpanel to outdoor workshop


50A Sub

I would run a new wire from the panel to the workshop. I would not splice AL to CU. There are too many conflicting reports. Purple wire nuts are rated for it, but I'm not sure they make them large enough for a #6 and #8. There might be some lugs that are rated for this purpose, but those could be on the pricey side.

These say they are rated for CU to AL...

http://www.polarisconnectors.com/pdfs/NSi/IT_series.pdf
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Old 08-01-2012, 08:10 PM   #4
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50A Sub

I would run a new wire from the panel to the workshop. I would not splice AL to CU. There are too many conflicting reports. Purple wire nuts are rated for it, but I'm not sure they make them large enough for a #6 and #8. There might be some lugs that are rated for this purpose, but those could be on the pricey side.

These say they are rated for CU to AL...

http://www.polarisconnectors.com/pdfs/NSi/IT_series.pdf
Just buy dual rated split bolts... super cheap and efficient.

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Old 08-01-2012, 08:16 PM   #5
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Subpanel to outdoor workshop


Is your range circuit 3 wire or 4 wire. If its just a 3 wire, you will need to run back to the (sub)panel.
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Old 08-01-2012, 08:26 PM   #6
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Hi folks,




Will be doing a UFER ground in the workshop slab.
I doubt this will work, since almost every slab requires a plastic as a vapor barrier, and to meet the requirements of a UFER ground, the slab must be in direct contact with the earth. Just a thought....
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Old 08-01-2012, 08:39 PM   #7
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Subpanel to outdoor workshop


My range circuit is 4 wires, 2 hots, 1 neutral, 1 ground.

I've been researching splicing copper to aluminum. You are right, there are some conflicting reports about this type of splicing. Some concerns are with the bending and over stressing the aluminum wire while creating a splice.

I'm torn between running a new circuit and splicing onto the existing wire.

Running a new circuit means running in the crawlspace and securing the wire per code to floor beams. If I do that then I think I'd do UF all the way since running conduit would be quite challenging and it goes underground once outside. I'd have to open a wall to bring it up into the panel. But, drywall is no big deal.

So, is #6 copper ok for a 60 amp breaker at the main subpanel? I could do a 100 amp sub in the workshop, but it would be limited by the 60 amp in the main sub.
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Old 08-01-2012, 08:41 PM   #8
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I doubt this will work, since almost every slab requires a plastic as a vapor barrier, and to meet the requirements of a UFER ground, the slab must be in direct contact with the earth. Just a thought....
What If there were re-bar in the slab, and bonded to a rod?
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Old 08-01-2012, 08:42 PM   #9
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The Ufer ground would be in the 12" x 12" footing that goes around the perimeter of the slab. You are correct that the slab would have a vapor barrier, but not the footing, which would be in direct contact with the soil.
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Old 08-01-2012, 08:42 PM   #10
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What If there were re-bar in the slab, and bonded to a rod?
The SLAB has to be in direct contact with the earth, other wise, plan on driving two rods.
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Old 08-01-2012, 08:44 PM   #11
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The Ufer ground would be in the 12" x 12" footing that goes around the perimeter of the slab. You are correct that the slab would have a vapor barrier, but not the footing, which would be in direct contact with the soil.
That's different, the way you worded it, I assumed you were doing a floating slab... You need 20' of rebar or #4 copper within the footing, just so you know.
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Old 08-01-2012, 08:51 PM   #12
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Subpanel to outdoor workshop


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That's different, the way you worded it, I assumed you were doing a floating slab... You need 20' of rebar or #4 copper within the footing, just so you know.
Yeah, sorry. I left that out of my original post. What do you say as to the UF wire size, panel and breakers? I don't plan to draw that much in the workshop. My compressor runs fine off the 20A garage circuit. And, in the winter I use a small heater, with the lights on, radio etc. So, my customary usage wouldn't go much beyond that.
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Old 08-01-2012, 08:56 PM   #13
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Quote:
Originally Posted by RM575 View Post
Yeah, sorry. I left that out of my original post. What do you say as to the UF wire size, panel and breakers? I don't plan to draw that much in the workshop. My compressor runs fine off the 20A garage circuit. And, in the winter I use a small heater, with the lights on, radio etc. So, my customary usage wouldn't go much beyond that.
We have to revisit the existing Range wire first, is this a SER type cable?
If it is, and it is #6 AL, the largest breaker you will be allowed is 40 amps...


EDIT-
(This is kind of touchy because of the code changes throughout the years) I would leave the existing 50 amp breaker and run #8 CU. THWN AWG out to the workshop....)

Last edited by stickboy1375; 08-01-2012 at 09:02 PM.
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Old 08-01-2012, 09:04 PM   #14
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Quote:
Originally Posted by stickboy1375 View Post
We have to revisit the existing Range wire first, is this a SER type cable?
If it is, and it is #6 AL, the largest breaker you will be allowed is 40 amps...


EDIT-
(This is kind of touchy because of the code changes throughout the years) I would leave the existing 50 amp breaker and run #8 CU. THWN AWG out to the workshop....)
I see your edit now, I was about to ask you about what you originally said.

He would be good with 50A on the Al #6 up until the 2008 code. If his area is on the 2011 he is again good with it unless it's in contact with insulation. Or at least that's the way I would understand it.
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Old 08-01-2012, 09:06 PM   #15
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I see your edit now, I was about to ask you about what you originally said.

He would be good with 50A on the Al #6 up until the 2008 code. If his area is on the 2011 he is again good with it unless it's in contact with insulation. Or at least that's the way I would understand it.
Isnt it crazy how they can change something so simple that was never an issue to begin with?

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