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Old 05-28-2012, 03:34 PM   #1
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Residential Romex #12 or #14 jacket temps


Those of you with IR meters, have you ever checked this?

I'm looking for data like
#14 copper
amb temp = 22C
current = 10A
jacket temp = ?C

or

#12 copper
amb temp = 30C
current = 15A
jacket temp = ?C

TIA

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Old 05-28-2012, 03:49 PM   #2
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Residential Romex #12 or #14 jacket temps


You have way too much time on you hands

I predict the jacket temp is very close to ambient.

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Old 05-28-2012, 03:57 PM   #3
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Residential Romex #12 or #14 jacket temps


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You have way too much time on you hands

I predict the jacket temp is very close to ambient.
Unless of course a serious problem is in the mist.
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Old 05-28-2012, 03:59 PM   #4
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Residential Romex #12 or #14 jacket temps


An IR thermometer won't be accurate enough to make this measurement. The temperature difference will be very small, and since the cable jacket has different emissivity than whatever the surroundings are, the error due to emissivity difference will make the actual temperature difference indistinguishable.
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Old 05-28-2012, 05:54 PM   #5
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Residential Romex #12 or #14 jacket temps


I put 25A through #14 copper once and it went about 2F above ambient as measured with a precision thermistor placed under the jacket. I haven't checked this value against the Neher-Mcgrath equation.

I'm trying to make sense of passing 30A through #12 in an HVAC setup without unduly shortening the life of the Romex insulation. Every 9C increase halves the life and 30A instead of 20A is a (30/20)^2 = 2.3x increase in insulation temp rise above ambient from whatever the 20A temp is.

For those philosophers on this forum - with the time on my hands I am trying to make sense of every decision I have ever made in my whole life, and it's not so easy!
Life is lived forward and understood backward.

Last edited by Yoyizit; 05-28-2012 at 05:58 PM.
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Old 05-28-2012, 06:07 PM   #6
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Residential Romex #12 or #14 jacket temps


The increased ampacity is only until the motor or compressor starts up. This is only several cycles of duration, not an extended period.
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Old 05-28-2012, 06:50 PM   #7
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Residential Romex #12 or #14 jacket temps


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Originally Posted by Yoyizit View Post
For those philosophers on this forum - with the time on my hands I am trying to make sense of every decision I have ever made in my whole life, and it's not so easy!
Life is lived forward and understood backward.
If EVERY decision you've ever made has been thought out and has made sense you must be one BORING person.

BTW, what kind of engineer are you.
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Old 05-28-2012, 06:53 PM   #8
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Residential Romex #12 or #14 jacket temps


Some of my decisions made sense at the time. In hindsight, maybe not so much.
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Old 05-28-2012, 06:56 PM   #9
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Residential Romex #12 or #14 jacket temps


Quote:
Originally Posted by Yoyizit View Post
.

I'm trying to make sense of passing 30A through #12 in an HVAC setup without unduly shortening the life of the Romex insulation.
Hey silly, 30A would never be allowed to flow through #12 AWG in an HVAC scenario, you know why? because the motor contains thermal overloads that would shut the motor off before it reached that amperage.

in simple terms, the motor is the load, so if the motor can't physically draw more than 25 amps, I guess the wire is pretty safe.
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Old 05-28-2012, 09:24 PM   #10
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Residential Romex #12 or #14 jacket temps


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I'm trying to make sense of passing 30A through #12 in an HVAC setup without unduly shortening the life of the Romex insulation.
That would not be a code compliant installation. That would require #10 wire. This is not complicated: the wire must be sized to the load. The breaker may be larger than the wire's allowable load current if other means exist to protect against sustained overloads. The overload protection may be located at the load-end of the circuit (as in a thermally protected motor) rather than the breaker-end because it doesn't matter where it is. The breaker provides ONLY short circuit protection. As long as the breaker's magnetic instant trip current is less than the bolted fault current, it would do its job safely.
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Old 05-28-2012, 10:02 PM   #11
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Residential Romex #12 or #14 jacket temps


Quote:
Originally Posted by Yoyizit View Post
I'm trying to make sense of passing 30A through #12 in an HVAC setup without unduly shortening the life of the Romex insulation.
See below for my comment.

Quote:
Originally Posted by mpoulton View Post
That would not be a code compliant installation. That would require #10 wire. This is not complicated: the wire must be sized to the load. The breaker may be larger than the wire's allowable load current if other means exist to protect against sustained overloads. The overload protection may be located at the load-end of the circuit (as in a thermally protected motor) rather than the breaker-end because it doesn't matter where it is. The breaker provides ONLY short circuit protection. As long as the breaker's magnetic instant trip current is less than the bolted fault current, it would do its job safely.
Well Mpoulton you are half right on one part but if no nameplate on the HVAC then it is a clear shot with code volation but once you know the nameplate rating like max amps and minum conductor size or running amp then I will sized it.

If need more info on that just look up 440.6 ( if I did recall that number correct )

Merci,
Marc
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Old 05-29-2012, 02:00 AM   #12
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Residential Romex #12 or #14 jacket temps


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Well Mpoulton you are half right on one part but if no nameplate on the HVAC then it is a clear shot with code volation but once you know the nameplate rating like max amps and minum conductor size or running amp then I will sized it.

If need more info on that just look up 440.6 ( if I did recall that number correct )
I think we're saying the same thing. Article 400 (and nameplate data that is specified in accordance with Article 400) allows conductors that are sized to the load, with OCPD that is substantially larger.

Last edited by mpoulton; 05-29-2012 at 12:55 PM.
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Old 05-29-2012, 05:54 AM   #13
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Residential Romex #12 or #14 jacket temps


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I think we're saying the same thing. Article 400 (and nameplate data that is specified in accordance with Article 400) allows conductors that are sized to the load, with OCDP that is substantially larger.
With that said, were also trying to bash the concept into Yoyizit's brain. lol...
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Old 05-29-2012, 09:39 AM   #14
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Residential Romex #12 or #14 jacket temps


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If EVERY decision you've ever made has been thought out and has made sense you must be one BORING person.
It's the grossly bad decisions that I made that I'm trying to figure out, after the fact, as in "What was I thinking?" and "Was I thinking at all?"

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