Ampacity of 12 THHN conductor

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Re: Ampacity of 12 THHN conductor

Originally posted by james wuebker:
So you are saying if I use #8 THWN and the equipment is marked 75 C I can put a 50 breaker on this. I don't agree if this is what your saying.
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That is exactly what I am saying.

If the terminals, equipment and conductor insulation are all rated at least 75 C you may use the 75 C column meaning the 8 AWG THWN is rated 50 amps.

I ask you to point to a code section that says otherwise. ;)

Bob
 
Re: Ampacity of 12 THHN conductor

iwire
Bob, will you point me in the direction in the code book that tells us what you are taking about. I'll get back with my answer after I take the kids to the Easter egg hunt.
Thanks!
Jim
 
Re: Ampacity of 12 THHN conductor

Jim, Larry and Iwire are on the money, why would you think a conductor of 75 deg insulation can not be used at it's rated ampacity if all terminations are also 75 deg.

BTW,I hope the Easter Egg hunt was fun. :)

Roger
 
Re: Ampacity of 12 THHN conductor

By james wuebker:
Alot of people don't understand the theory about these tables and how to use them correctly
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I'm still not completely comfortable with this area.

So Larry, you're saying the 60? side of the 60?/75? marking is how hot the device is expected to operate and the 75? side is what the terminal is rated to withstand?
 
Re: Ampacity of 12 THHN conductor

Originally posted by physis:
By james wuebker:
Alot of people don't understand the theory about these tables and how to use them correctly
Click to expand...
I'm still not completely comfortable with this area.

So Larry, you're saying the 60? side of the 60?/75? marking is how hot the device is expected to operate and the 75? side is what the terminal is rated to withstand?
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Kind of. Say we have a 100amp C/B. The heat created by the current flow through the C/B will not damage 60'C conductor insulation. Conversley, the heat given off by 75'C wire operating at max ampacity will not damage the C/B.

Better ?
 
Re: Ampacity of 12 THHN conductor

Ok.
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Re: Ampacity of 12 THHN conductor

Got it. Missed the significance of "only", as in the UL White Book "75C ONLY"

Makes sense now

Thank you

carl
 
Re: Ampacity of 12 THHN conductor

Alright Larry, what do I do with this:

Square D HOM, has a real big 40?C directly over the wire strip gauge.

and this much smaller, over a ways for terminals: #14-#8 blah blah 60?/75?C.

[ March 28, 2005, 02:19 PM: Message edited by: physis ]
 
Re: Ampacity of 12 THHN conductor

Originally posted by physis:
Alright Larry, what do I do with this:

Square D HOM, has a real big 40?C directly over the wire strip gauge.
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The 40 C is the allowable ambient temp.
 
Re: Ampacity of 12 THHN conductor

Where do you get that from?

And why does it seem so disorganized?
 
Re: Ampacity of 12 THHN conductor

Did I do the math right? 104? F.

That wont fly in the mountains.
 
Re: Ampacity of 12 THHN conductor

Originally posted by physis:
Where do you get that from?
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Sam, you can go to this Sq D page type in "40 deg" in the search window and "circuit breaker" in the drop down menu to hear it from them.

Roger
 
Re: Ampacity of 12 THHN conductor

Not NEC, UL?

I'm probably being difficult but this stuff's already more fuzzy than it should be.

And I am trying to avoid studying all this /again\. :(
 
Re: Ampacity of 12 THHN conductor

So the 40?C. marking is implied without the "re-marking" of 60?C. In this case that marking is there dispite that it would be infered.

Shouldn't there be an indication of what that particular marking defines?

This is clear as mud.
 
Re: Ampacity of 12 THHN conductor

Originally posted by tom baker: is the ampacity of a 12 THHN conductor 20 amperes?
If not where does it say otherwise.
Why do so many electricians feel it is 20 amperes
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OK, Tom. You've dropped this amusing anecdote upon us, and then you went away. Are you sitting back and chuckling at the responses, or are you going to tell us the reason for the question?

Here?s my response: It is never, never, never correct to say, ?The ampacity of (insert a wire size) is (insert a number) amps.? ;)
 
Re: Ampacity of 12 THHN conductor

Originally posted by physis:
So the 40?C. marking is implied without the "re-marking" of 60?C. In this case that marking is there dispite that it would be infered.
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Sam I do not understand.

40 C is the maximum temperature of the area that the breaker can be operated in.

This has nothing to do with the 60 C, 75 C or 60/75 C terminal ratings.

For further confusion the breaker can be 're-rated' for use above 40 C but lets just forget about that. :D
 
Re: Ampacity of 12 THHN conductor

Well, then I'll rephrase the question.

How am I supposed to know, by looking at the markings on the device, what it is talking about?

These markings, in my opinion, are just asking to be confused with other required markings!

I know I'm getting kind a grumpy from this, but it's all very messy.
 
Re: Ampacity of 12 THHN conductor

Originally posted by physis:
How am I supposed to know, by looking at the markings on the device, what it is talking about?
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You know this because you are a highly qualified electrician. :)

I would like to see a standard labeling scheme and placement.

The placement should be such that it can be seen without the removal of the breaker.
 
Re: Ampacity of 12 THHN conductor

That too, I agree we should be able to see the ratings without pulling breakers out.
 
Re: Ampacity of 12 THHN conductor

And lord help us with the hordes of so called proffesionals who don't give a rat's behind.

[ March 28, 2005, 04:49 PM: Message edited by: physis ]
 
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