Ampacity of 12 THHN conductor

[paul]

Re: Ampacity of 12 THHN conductor

The ampacity of #12 better be more than that in my house, cus I've got a Zinsco breaker protecting it! Is 'protecting' the correct word in reference to Zinsco breakers?

 

[sandsnow]

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.

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

Thanks for filling in for me Bob and Rodger. We wouldn't want Sam to lose any more sleep. He's already pretty stressed over the SA dining room thread.

 

[james wuebker]

Re: Ampacity of 12 THHN conductor

iwire
I have to said that I was wrong in the earlier statement I made. You were correct. If the breaker is rated at 75 c and the device is rated at 75 c, you can use the amp rated in the 75 c table. You also most use a insulation of 75c or higher also, but you know that already. You are correct in saying this and thank you for telling me this. Maybe it was just a brain fart on my part that day.
Jim

 

[abode electric]

Re: Ampacity of 12 THHN conductor

The ampacity of #12 is 30 amps. There are many other factors witch determine what the safe or maximum load that it can carry.

 

[roger]

Re: Ampacity of 12 THHN conductor

Originally posted by sandsnow:

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.

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

Thanks for filling in for me Bob and Rodger. We wouldn't want Sam to lose any more sleep. He's already pretty stressed over the SA dining room thread.

No problem Larry, we all have to worry about Sam's sleep and stress.

Roger

 

[physis]

Re: Ampacity of 12 THHN conductor

I know, you expect me to get gat all angry and stuff. But I'm not going to. Why? Well because Mr. Flame Guy thinks that this is an important issue. Here, listen to what Mr. Flame Guy has to say about it for yourselves.

Well, well Sam's right you know.

[ March 28, 2005, 11:59 PM: Message edited by: physis ]

 

[pierre]

Re: Ampacity of 12 THHN conductor

From Roger's lead to this link, SqD website information page - it is very informative and very smart on their part:


"Question What is the ambient operating temperature of a circuit breaker?"

"Answer Circuit breakers are calibrated for use at 40 degree C. They should be re-rated if used at temperatures below 25 degrees C or above 40 degrees C."


Most of us take circuit breakers for granted. We have been installing them for so long and basically forget about them, just assuming they are going to function when necessary.

There are volumes of information on the web about circuit breakers, very easy to find, weeks of good reading .

Sometimes we wonder how much should we know? This industry provides us with a never ending stream of information to learn... each individual chooses how much he will learn through the various channels of learning - on the job, classes, seminars, web related, etc...
Some just choose to learn more than others - some think they know, those are the most dangerous types.

 

[sandsnow]

Re: Ampacity of 12 THHN conductor

Originally posted by pierre:

Some just choose to learn more than others - some think they know, those are the most dangerous types.

Well said, Pierre

It wasn't until I came to this forum and was challenged, did I realize just how "dangerous" I had become.

 

[hurk27]

Re: Ampacity of 12 THHN conductor

"Answer Circuit breakers are calibrated for use at 40 degree C. They should be re-rated if used at temperatures below 25 degrees C or above 40 degrees C."

I use to have a chart for this for Sq.D and CH breakers as one of the plants I worked at wasn't heated and we had to derate the breaker as the "ambient operating temperature" could get as low as "0?C" in the plant and breakers can allow allot more current at that temp.

 

[sandsnow]

Re: Ampacity of 12 THHN conductor

Originally posted by hurk27:

I use to have a chart for this for Sq.D and CH breakers as one of the plants I worked at wasn't heated and we had to derate the breaker as the "ambient operating temperature" could get as low as "0?C" in the plant and breakers can allow allot more current at that temp. [/QUOTE]
That's interesting. Do you remember any details. Did you use a 15amp c/b for a 20amp circuit? Did you use the mean, average, or absolute lowest temp?

 

[tom baker]

Re: Ampacity of 12 THHN conductor

All-Thanks for your comments. this was to be an example to use in a class I was instructing that day, but later in the day I could not access the wireless network.
Its 30 amperes.
Understanding the ampacity correctly can save a lot of money in an installation.

[ March 29, 2005, 02:40 PM: Message edited by: tom baker ]

 

[tom baker]

Re: Ampacity of 12 THHN conductor

"As pointed out already by the really smart guys, 240.4(D) Is probably what everyone automatically thinks of. But as we all know there are exceptions to every rule. This is the NEC after all!"
240.4(D) used to be the 'obilisk' note to 310.16.
Then it was moved as it had nothing to do with 310.16

 

[physis]

Re: Ampacity of 12 THHN conductor

It's funny how there are no simple answers in the NEC. It doesn't much matter how simple the question might be.