NM cable

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  #1  
Old 11-26-06, 07:16 PM
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NM cable

What size cable do I need for 40, 50, and 60 amp circuits. I am a little confused by the derating for small wires 14, 12, 10. Does this have any bearing on 8, 6?
 
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  #2  
Old 11-26-06, 07:52 PM
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Question

Why do you ask? Explain what you want and need.
Your question is too vague.
 
  #3  
Old 11-26-06, 08:02 PM
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I don't see anything vague about it. I simply want to know what size NM is required for 40, 50 and 60 amp circuits.
 

Last edited by trapper22-250; 11-26-06 at 08:26 PM. Reason: spelling
  #4  
Old 11-26-06, 08:08 PM
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Question

Originally Posted by trapper22-250
What size cable do I need for 40, 50, and 60 amp circuits. I am a little confused by the derating for small wires 14, 12, 10. Does this have any bearing on 8, 6?

NONE OF THE ABOVE !! Are suitable for the question.

Your all over the place.

With all due respect, Try again.
What is your question!!?
 
  #5  
Old 11-26-06, 09:19 PM
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You question is quite clear, but is not specific enough to let us give you a specific answer. My attempt at answering the general question:

All other things being equal ('normal loads', 'normal ambient temperature', 'no bundling', etc.) to properly size NM cable you simply use the 60C column of table 310.16. For a 40A circuit you would need #8, for a 50A circuit you would need #6 (good for up to 55A), and for a 60A circuit you would need #4 (good for up to 70A).

The rule regarding 'derating of small wires' is 240.4(D) and applies only to #14, #12, and #10 conductors. This is not actually about derating, but instead forced by the capabilities of circuit breakers to properly protect wires during short circuit conditions. 'Derating' is used to describe the reduction in ampacity caused by ambient temperature or conductor bundling.

Depending upon the specifics of the situation you might be required to use larger conductors, or you might be able to safely use smaller conductors. For example if you have a load that requires a conductor ampacity of between 50 and 55A, you could safely use #6 conductors _protected_ by a 60A breaker. This does not mean that you can run up to 60A of load on #6 conductors, simply that the conductors can be loaded up to 55A yet protected at 60A. On the other side of the coin you might have temperature considerations that force you to use larger conductors. Further, you might find that using other cable types, or conductors in conduit, permits you to use the 75C column, which makes #6 copper good for up to 65A. There are a number of restrictions to using the 75C column, but given copper prices this is often something worth exploring.

With so many details to consider there really is not specific answer without knowing the details of the installation being contemplated.

-Jon
 
  #6  
Old 11-26-06, 09:38 PM
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Yea, what he said!!!

You got my Vote!!!

Thanks Winnie.

Trapper,
I hope you don't think I was being difficult. That was not my intention. There are (as noted) so many variables, I was trying to narrow something down.
I think it's awesome that we want to learn.
You can never know to much.
 
  #7  
Old 11-27-06, 04:42 AM
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Thanks for the replies
 
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