Help with choosing correct gauge wire

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  #1  
Old 03-17-11, 10:55 AM
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Help with choosing correct gauge wire

Hello everyone,

This is my first post on this great site. I have a question reguarding a sub panel I am putting in my garage. First, I have a 200a panel in the basement. The sub is about 25-30ft away. There, I have a 125a QO Square D. It will hold 8- 20a breakers,1- 50a breaker, 3- 15a breakers, and 1- 30a breaker. What Gauge wires do I need for hot/neutral/ground? Also, how is the sub grounded? I am in SW Wisconsin.

Thanks,
Ryan
 
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Old 03-17-11, 11:16 AM
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Welcome to the forum. Attached or detached garage? What loads will be at garage? Any electric heaters, welders, compressors, stationary tools, etc, or just lights?
 
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Old 03-17-11, 11:56 AM
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The important information is what those breakers will be powering, and will this be an attached garage? If this is a workshop, let us know what kind and how many tools will be running at the same time.

The sub is grounded by means of the "equipment grounding conductor", which is usually a bare or green wire pulled along with the hot and neutral conductors from the main panel. If this is a detached garage, then the sub panel is also grounded to the earth using grounding electrodes (usually copper clad rods).
 
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Old 03-17-11, 01:31 PM
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I plan on running a single phase compressor, Miller 251 welder, and some hand power tools. It is an attached garage that I plan on doing hobby work out of. The bigger sub is in case I plan on using bigger equipment later.

Thanks Guys
 
  #5  
Old 03-17-11, 01:38 PM
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I would recommend a 100A feeder. Install a 100A double-pole breaker in your main panel. From that run a #2 copper or #1/0 aluminum SER four-conductor cable to the subpanel. The neutral and ground conductors in the cable assembly may be a reduced size such as #2-2-4-6. You may need to buy a neutral lug kit to land the large gauge neutral conductor on the neutral bus in your main panel. If you choose the aluminum cable option, use noalox grease on the terminations. If your electrical supplier has it in stock you can use #2-2-2-8 NM-B cable instead of SER.

The subpanel needs an add-on ground bar kit and should have the neutral bonder removed per the panel instructions.
 
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Old 03-17-11, 01:45 PM
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I have the ground bar add on and the larger lug for the neutral, but not sure what #2-2-4-6 is. Can you enlighten me? Never mind that. Figured it out. Can this be put in schedule 80 2"?

Thanks again!
 
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Old 03-17-11, 02:30 PM
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The #2-2-4-6 is an SER cable with two #2 hots, a #4 neutral and a #6 ground. Depending on what the supplier has in stock it might be close to that, but the important part is that the hots be at least #2 and the ground be at least #8. (All sizes assuming copper here).

If you're going to use a fully assembled conduit between the two panels then you should pull individual conductors instead of a pre-assembled cable like SER or NM-B. In the conduit you can pull #3 THHN for the hots and neutral. They can all be black, but put white tape on the last 6" of each end of the neutral wire. The ground should be bare or green #8. Wires in conduit have a different temperature rating so you can use slightly smaller sizes.
 
  #8  
Old 03-17-11, 07:28 PM
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Thank you Ibpooks! Exactly what I was lookin for.
 
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