Will 8/3 Romex meet NEC for 50amps?

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  #1  
Old 09-09-11, 08:45 AM
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Will 8/3 Romex meet NEC for 50amps?

I'm getting ready to setup a generator hookup to my panel using an interlock setup. The generator (Generac 15000E) is rated at 15kw continuous and I will be using the 50amp outlet.

I spoke with a friend of mine, who's family does commercial electric, and was told I need to use 6/3 romex from my panel to the 50amp inlet. The run from the panel to the inlet will be less then 50ft... 50ft is if I decide to put the inlet on the other side of the house and it could be as short as 5 feet. The chart at the local box store says I can use 8/3... So the question...

What does NEC 2011 say? Do I have to use 6/3 or will 8/3 meet code?

Money is an issue and I hate working with thick wire! ..... Regardless, I have to meet code and the county permit office won't tell the the code... They just keep telling me to go to NEC 2011 for the info.

Thanks!
 
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Old 09-09-11, 08:57 AM
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If you use conduit and THWN yes but NM-b or UF no. The latter two types must be #6.

NM-b (AKA Romex) Ampacity chart:

http://www.encorewire.com/wp-content...reWire-NMB.pdf
 

Last edited by ray2047; 09-09-11 at 09:17 AM.
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Old 09-09-11, 09:01 AM
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The chart at the local box store says I can use 8/3... So the question...
The charts, and far too often the clerks, at the big box stores are notorious for dispensing incorrect information. Always check this forum for the latest code requirements. We have active electricians, electrical engineers and even people that read code before going to sleep on this board and we DO have a huge base of information.
 
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Old 09-09-11, 09:25 AM
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6/3 it is then!! Thanks folks!!
 
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Old 09-09-11, 09:52 AM
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The chart may have been a 90 chart. The wires within the cable assembly are rated 90 but the cable is for rating purposes considered 60 so you must use the 60 column in the NEC chart. Pros correct me if I am wrong.
 
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Old 09-09-11, 11:43 AM
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(For anyone else listening) Those charts in the big box stores are wrong for the vast majority of situations. They display the 90C ampacity or the table 310.15(B)(6) ampacity for the individual conductors which are not applicable in almost all typical wiring jobs.

It's sort of like giving out the top speed of a car. It's irrelevant because the speed limit is going to be less than that 99.999% of the time you use the car.
 
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Old 09-09-11, 12:56 PM
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Originally Posted by ray2047 View Post
The chart may have been a 90 chart. The wires within the cable assembly are rated 90 but the cable is for rating purposes considered 60 so you must use the 60 column in the NEC chart. Pros correct me if I am wrong.
You are correct. NM-b and UF cable (other as well) is limited to the 60 degree column max. Derateing is started at the 90 degree but, when it is all said and done, it is the 60 degree column max.
 
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Old 09-09-11, 04:29 PM
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Originally Posted by Furd View Post
The charts, and far too often the clerks, at the big box stores are notorious for dispensing incorrect information. Always check this forum for the latest code requirements. We have active electricians, electrical engineers and even people that read code before going to sleep on this board and we DO have a huge base of information.
How do you know who reads the code before bed? grin
 
  #9  
Old 09-09-11, 06:59 PM
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I was thinking of our young friend, Justin but if the shoe fits...

Truth is, I sometimes read codes for relaxation. Back when I was married my wife would remark that she couldn't understand how I could read technical manuals (and codes) the way she read novels.

And Justin, you're not weird because I used to do all the same things that you do. Or maybe that makes me weird?
 
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