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Discussion Starter #21
Speaking of code....Is it code allowed to do as I am planning to use a 60 amp double pole breaker at my main panel to feed the 100 amp subpanel? I plan to use 6/3 NM - B as my feeder cable, but it looks like 6-gauge wire is for 50 amps? While I am asking more questions, I plan to run 14-2 NM cable to my 15 amp circuits using a 15 amp breaker in the sub-panel and 15 amp rated receptacles. For the 20 amp circuits I plan to use 12-2 NM cable with 20 amp breakers and 20 amp receptacles? Also I plan to use GFI receptacles in the barn, however, no water is near. Should I use regular receptacles or is GFI the correct way to go? Do all receptacles in a GFI circuit have to be GFI receptacles, or just the first in the circuit? Sorry for the questions, remember I am only a DIY Homeowner. I once again appreciate any information that you can send my way and thanks for taking the time to be involved in my project.
 

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I would assume that a barn is treated the same way a garage is treated, as a wet location, because like a garage there is the potential for wet equipment to be driven into it. GFCI protection is required on all receps in a garage (as well as tamper resistant) and thus I'd assume it applies to the barn as well.

20 amp circuit with 12 ga wire and 20 amp breaker can use 15 amp duplex receptacles because it's rated for 15 amps for each individual plug so the whole duplex receptacle can handle 20 amps.

Now if was a single receptacle it would be required to be 20 amps.

Looking at table 310.16, 6 ga. copper is good at 75 degrees C to 65 amps so it should be fine for a 60 amp circuit. Were you looking at the aluminum column?
 

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Discussion Starter #24
Thanks again. I am actually looking at a book for the ampacity. I assume that you are more likely to be correct on your numbers. The cable that I am looking at from Home Depot is Cerrowire 6/3 NM-B. It has 3 #6 copper wires and 1 # 10 copper ground. I assume that THHN is rated the same if this wire is copper also? So it should handle the 60 amp sub-panel. I will install all GFI plugs because of the wet possibility. Can I use 20 amp duplex receptacles in the 20 amp circuits if I would like to? I assume that 15 amp would be cheaper, but 20 amp would make sure that it can handle the possible load? I will use 20 amp breakers and 12-2 wire to feed the circuits. Can I choose to use 20 amp duplex receptacles? Thanks to WillK and Missouri Bound for responding, I appreciare it.
 

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20A receptacles are allowable if you want to spend the extra money.
 
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Discussion Starter #26
I just looked at the specifications listed on the Home Depot web site for the 6/3 NM-B feeder cable that I am thinking of using for the subpanel and it says the allowable ampacities is 55 amps for the wire. Does this mean it is too small for my project? I found a chart for # 6 gauge ampacity and it said that at 60 degrees C it is rated for 55 amps, at 75 degrees C rated for 65 amps, and at 90 degrees C rated for 75 amps. Looks like the THHN wire has a higher amp capacity? Maybe because it is not enclosed? Please let me know your thoughts on the 6/3 and the 60 amp double pole breaker feeding the subpanel. Maybe I should use a 50 amp double pole breaker, if there is such a thing? Or larger wire, # 4? Thanks
 

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#6 Cu THHN can be derated off the 90* column, but most likely would fall into the 75* column at best. Rarely are you going to find terminals rated for 90*, and both terminals at each end of the wire would have to be rated 90* to be able to use the 90* column.

6/3 NM cable used as a feeder would put it in the 60* column at 55 amps, but is allowed to be protected by a 60A breaker.

Yes, the barn would require GFCI protected receptacles, if not intended to be habitable (which most likely is not).
 

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Discussion Starter #28
Thanks SD515, I appreciate the support. Thanks for explaining the ampacity ratings, now it makes more sense. I had assumed that the 60 degrees C column was the one for me. Sounds like the 6/3 NM-B cable will work for me. I will use the double pole 60 amp breaker at the main panel. Is it safe and okay to install a 100 amp subpanel with this setup? I did do a load evaulation and came up with 57.7 amps needed at full capacity, which will never happen. The 60 amps should be plenty of power. The 100 amp subpanel will give me the 10 circuits needed. Please verify if my thinking is correct on this one, I want to be safe. Thanks again.
 

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The 100 amp rating of the panel is the maximum it can safely carry. Anthing less, like your 60 amp supply is fine.

Are you planning on the 6-3 Nm being outside?
 

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Discussion Starter #30
Hi Jim, thanks for responding. The 6/3 NM -B cable will all be inside. The main panel is in my basement and the 6/3 cable will run on the floor joists in my cellar, then under the pantry(which is a crawlspace). Once in the woodshed and barn, the cable will be run overhead to keep away from animals that might want to munch on. I am thinking about using a conduit under the pantry crawlspace, like 12-15 feet of the run, to further protect the expensive 6/3 cable. There is about 125 feet between my main panel and sub-panel and ALL indoors. Thanks to everyone once again.

PS Thanks for the info on the 60 amp breaker feeding the 100 amp sub-panel. Makes me feel better with all this great advice.
 

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Discussion Starter #31
I just had a conversation with a local electrician that will view my project soon and he recommends using Aluminum # 4, with 4 wire cable to feed my sub-panel? He also would use the 60 amp double pole breaker in the main panel as we were planning to use. I have been looking at the 6/3 NM-B cable to use as a feeder cable. Not sure what the difference between copper and aluminum is? I guess there is a cost savings? Would you recommend using copper or aluminum? Just curious of what is the general practice. Thanks again.
 

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I just had a conversation with a local electrician that will view my project soon and he recommends using Aluminum # 4, with 4 wire cable to feed my sub-panel? He also would use the 60 amp double pole breaker in the main panel as we were planning to use. I have been looking at the 6/3 NM-B cable to use as a feeder cable. Not sure what the difference between copper and aluminum is? I guess there is a cost savings? Would you recommend using copper or aluminum? Just curious of what is the general practice. Thanks again.
I don't know the prices on the smaller sizes like that, but let's put it this way. The difference between copper and aluminum for my 30' garage feeder at 100 amps was the difference between $100 and $360.
 

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Discussion Starter #33
Was the $100 for aluminum and $360 for copper? The electrician told me the aluminum # 4 was $1.25 a foot. The 6/3 NM-B was $2.00 a foot. Is aluminum as good as copper or is it not worth the savings? How about safety?
 

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Aluminum is just as good as copper. The difference is the ampacity for the same size wire as you already know. The service to your home is aluminum.
 

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Discussion Starter #35
Thanks again for all of the support with this project, I appreciate it. I had to refresh my memory and took another look at the ampacity chart. Looks like #6 copper and # 4 aluminum are rated the same. So if I use copper #6 or aluminum #4, it will give me exactly the same ampacity and should be plenty to feed my sub-panel. And I would be able to save some money on the wire, which is always a good thing.
 
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