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Old 07-24-2007, 09:50 AM   #1
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temperature rating for Romex


Where does Romex (NM) fall in the temperature scale according to 2005NEC (60C,75C, or 90C)?
I checked the wire but don't see any indication.

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Old 07-24-2007, 09:59 AM   #2
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temperature rating for Romex


Did you strip the sheathing back and look at the markings on the individual conductor insulation?

According to SouthWire ;

Quote:

Type NM-B (nonmetallic-sheathed cable) may be used for both exposed and concealed
work in normally dry locations at temperatures not to exceed 90C (with ampacity limited to that for 60C conductors) as
specified in the National Electrical Code



Just curious... why do you ask?


Last edited by SecretSquirrel; 07-24-2007 at 10:04 AM.
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Old 07-24-2007, 10:02 AM   #3
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temperature rating for Romex


Ah, it's on the individual conductor. I'm asking so that I know which column to look at for derating.
So to continue, am I reading this right; a 90C 14AWG conductor can carry 25Amps if it doesn't need derating? Table 310.16
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Last edited by Clutchcargo; 07-24-2007 at 10:18 AM. Reason: wrong table
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Old 07-24-2007, 10:16 AM   #4
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temperature rating for Romex


Quote:
Originally Posted by Clutchcargo View Post
Ah, it's on the individual conductor. I'm asking so that I know which column to look at for derating.
So to continue, am I reading this right; a 90C 14AWG conductor can carry 25Amps if it doesn't need derating? Table 316.16
Now hold on one minute... I'm interpreting the phrase 'with ampacity limited to that for 60C conductors" meaning that you must treat it as 60 deg wire despite the fact the individual conductor rating is for 90 deg.

Secondly, you cannot play the overrating game if your overcurrent protection is not also suited for the same temperature rating. Most residential circuit breakers are rated for 75 deg C. You can't slap 90 deg wire on there expecting to use a smaller conductor. The inspector won't let you get away with that. At least that was my understanding. Someone correct me if I'm wrong.

Last edited by SecretSquirrel; 07-24-2007 at 10:18 AM. Reason: spelling
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Old 07-24-2007, 10:27 AM   #5
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temperature rating for Romex


Don't get me wrong, I'm not trying to overclock my electrical system like you would a computer.
According to that the NEC table 310.16 the 60C column, 14Awg conductor can carry 20Amps and 12AWG can carry 25Amps.

Does that mean you can bundle these together so that for:
15AMP circuit using 14Awg wire you can derate up to 75% before you need to increase condutor size?
20AMP circuit using 12Awg conductors, you can derate up to 80% without going to a smaller breaker or increasing conductor size?
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Old 07-24-2007, 10:43 AM   #6
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temperature rating for Romex


For derating purposes you can use the 90C column for NM-B, but you cannot exceed 15A, 20A, or 30A overcurrent protection for 14, 12, 10 gauge wire , respectively (with some exceptions). For example, if you have four 12/2 cables bundled together (8 conductors) you derate the wire by 70% using the 90C column. Since .7x30=21, you are still above 20 and may use a 20A breaker. However, if you bundle five 12/2, you now must derate 50%, reducing the ampacity to 15A and requiring you to use a 15A breaker to protect the circuits.
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Old 07-24-2007, 06:43 PM   #7
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temperature rating for Romex


Quote:
Originally Posted by Clutchcargo View Post
Ah, it's on the individual conductor. I'm asking so that I know which column to look at for derating.
So to continue, am I reading this right; a 90C 14AWG conductor can carry 25Amps if it doesn't need derating? Table 310.16
Bottom line:

14ga 15amps
12ga 20amps
10ga 30amps
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Old 07-24-2007, 06:54 PM   #8
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temperature rating for Romex


HouseHelper is right on.

You also have to be on the same page as to what "bundling" is. Around here simply running cables through holes is NOT bundling. And I absolutely agree.
Strapping or tying them together is.

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Answers based on the 2008 & 2011 NEC.
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