Subpanel in garage

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  #1  
Old 10-21-07, 07:03 PM
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Subpanel in garage

I know I've seen the answer here (I think) but can't find it so sorry about the redundant question.

I'm changing from overhead to underground for my service to the garage. Already have the subpanel and a 100 amp breaker in the main panel. What size wires and size conduit would I need for an about 75' run from main to sub. About 30' underground and 45' inside, all protected in conduit.

From what I've read I think I need THWN #3 copper in 1 1/4" PVC. Can the neutral or ground be a different size? Is copper the way to go, or maybe aluminum?

Thanks
 
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  #2  
Old 10-21-07, 08:23 PM
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Do you really need 100 amps? That's a whopping amount of power. If you really need that much, you might be overloading your main panel. Did you do a demand load calculation?

Yes #3 copper will be good. Some inspectors might allow #4 copper. Some inspectors also might allow #2 aluminum.

Keep the neutral the same size as the hots. The equipment grounding conductor can be smaller, #8 copper or #6 aluminum. You'll need a grounding rod and a GEC too. Verify your plans with your inspector before starting.
 
  #3  
Old 10-22-07, 04:47 AM
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I was just going with the 100 amps because thats whats there now. I mainly have lights, air compressor, and some hand tools in the garage. I probably could go smaller, but I also have plans on running a subpanel down to my barn (mainly for lights and some outlets) in the future from the garage, probably a 60amp.

Thanks for the help
 
  #4  
Old 10-22-07, 04:51 AM
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What is GEC? I already have a ground rod at the subpanel, do I need two 6' apart?
 
  #5  
Old 10-22-07, 07:02 AM
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GEC is a grounding electrode conductor, the heavy copper wire that runs from your ground rod to the grounding bar in your subpanel.

Depending on soil conditions in your area, you may need one or two grounding rods. Consult with your inspector, or just install two.
 
  #6  
Old 10-22-07, 07:42 AM
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rjels - Not an electrician, but FWIW I installed a 60 amp subpanel in my garage. It provides lighting and GP circuits, powers two door openers and two 20 amp circuits for power tools. I have a fairly well equipped workshop over the garage with some high demand stationary tools. I've never had a problem with power.
 
  #7  
Old 10-22-07, 06:07 PM
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What size wire would I need for a 60 amp subpanel? I really don't need a 100 amp just was thinking of what was there to begin with. I run 2 garage door openers, some lighting in the garage, and hand power tools, and an air compressor in the near future. I plan on running some power to a small barn about 200 feet away from this subpanel, thinking a 60 amp sub also. That would be lighting and some outlets, maybe a couple heaters to keep water troughs from freezing if we get some animals.

Would running a 60 amp subpanel off a 60 amp subpanel be fine, as long as I don't exceed the 60 amps overall?

Thanks
 
  #8  
Old 10-22-07, 08:07 PM
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60 amps only requires #6 copper wire, much easier and cheaper.

200 feet is a long way, especially on top of the 80 feet. Make sure you take voltage drop into consideration. But it sounds like your needs are modest enough to not be a problem.

One reason you might want to stay with the 100-amp panel is if you plan on a large welder, or a kiln, or perhaps a large air conditioner or significant resistance heating. Otherwise, I think 60 amps is plenty.

The answer to your final question is "yes".
 
  #9  
Old 10-23-07, 01:13 PM
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Thanks for all the help John.

I think I'll go with the 60amp panel, after looking at the price difference in copper. What size ground will I need and should I stay with 1 1/2 conduit for an easier pull?
 
  #10  
Old 10-23-07, 01:27 PM
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A 60A feeder with #6 copper requires a #10 copper ground.
 
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