What size and type of wire do I need for my subpanel?

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Old 03-05-13, 02:03 PM
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What size and type of wire do I need for my subpanel?

Hey,

I live in southern Ontario. I'm putting in a 100amp 120v subpanel into my workshop. I'm trying to figure out the type and size of wire I need. The subpanel is between 75 and 80 feet from the main panel and will run underground.

I'm wondering about using a a 2/0 aluminum service wire because it's much cheaper than copper. Will this work?

Thanks,

Ian
 
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Old 03-05-13, 02:11 PM
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Normally it is better to install a 120/240 subpanel both because it gives you more power for your bucks and because 120 volt service panels are almost as rare as hens teeth and more expensive.

The size wire you use depends on the size breaker you plan to use at the main panel. The size breaker at the main panel depends on anticipated loads likely to be use at the same time. If all 120 volt circuits off the subpanel then either a 30 amp breaker and #10 or a 60 amp breaker and #6. It is very unlikely you would need 2/0. Tells us the loads and we can go from there.
 
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Old 03-05-13, 02:22 PM
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Sorry to be unclear. It will be a 120/240 panel, but I only need 120. I'm looking at 4, 15amp breakers at the subpanel, but want to be able to add another couple later if I want to. And I also want to be able to run several circuits at once, as there are often several people working in there. So I will likely have a 60amp breaker at the main panel.
 
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Old 03-05-13, 02:26 PM
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Just as a price comparison I asked about #6 copper as opposed the 2/0 aluminum. The aluminum is $4.25/m, the copper is $10.75/m.
 
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Old 03-05-13, 10:37 PM
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Just as a price comparison I asked about #6 copper as opposed the 2/0 aluminum. The aluminum is $4.25/m, the copper is $10.75/m.
That's a big difference and you don't even need 2/0 aluminum for a 60A feed.
 
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Old 03-05-13, 11:35 PM
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Assuming a 60 amp feed you could go with #4 aluminum THWN or use a 50 amp breaker and go with #6 aluminum THWN. You will probably need to get that probably from a supply house.

Question for Pros: Can he re-designate black #4 as neutral and ground?
 
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Old 03-06-13, 09:33 AM
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Question for Pros: Can he re-designate black #4 as neutral and ground?
In the US and under the NEC, yes. That's larger than #6. Canada may have different standards.
 
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Old 03-06-13, 02:13 PM
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In the US and under the NEC, yes. That's larger than #6. Canada may have different standards.
Just thinking he might want to look at five hundred foot rolls of black #4 aluminum and compare to the price of four one hundred foot rolls of assorted colors. Probably cheaper to go with one hundred foot rolls especially since he can use #8 aluminum for ground (EGC not GEC).
 
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Old 03-06-13, 07:31 PM
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Thanks, for the advice so far. So to summarize.

If I'm using a 60 amp feed, then I can go with #4 aluminum THWN?

If I'm using a 50 amp feed, then I can go with #6 aluminum THWN wire right?

Either way I could use 2/0 aluminum wire, although it would be overkill?

Also ray2047, what do you mean by a 'supply house'? Just a store that sells electrical supplies only, instead of home depot or whatever? So far, I've been pricing stuff at a local electrical supply store, as well as a chain called Idea Supply...
 
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Old 03-06-13, 09:08 PM
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Supply house is one that sells mostly to the trade. The trade being electricians. It sounds like you have been looking in the right places. I am baffled by why you want to use 2/0 wire. It will almost certainly be more expensive than a smaller wire, very difficult to work with, and probably require pigtailing to smaller wire because it won't fit a 60 amp breaker.
 
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Old 03-06-13, 09:51 PM
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f I'm using a 50 amp feed, then I can go with #6 aluminum THWN wire right?
#6 aluminum XHHW .
 
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Old 03-07-13, 06:45 AM
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What's the difference between THWN and XHHW wire. I did a quick google, and people mentioned a few advantages (better in lower temperatures, when melting stays on the wire as opposed to dripping, and is more inedible to pests) but also that it is usually about 20% more expensive (i will check on the prices of stuff today). What makes it worth the extra cost?
 
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Old 03-07-13, 05:39 PM
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Aluminum THHN/THWN wire is available, but usually on special order in my area, I have never seen any. Type XHHW is what is uaually used when using aluminum. It could be different in Canada. Either is a good choice for outdoor/underground work. Neither has insulation that pests would bother.
 
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