Romex cable warm under heavy continuous use

K

Kornfeld

Member
Location
Palo Alto, CA
Occupation
Software Engineer
I have an electric car plugged into a 15amp circuit where the car is supposed to be drawing 12 amps. The outlet is fed by gauge 14 Romex and the outlet the car is plugged into is downstream from the GFCI, also connected with gauge 14 Romex. I noticed that GFCI was getting a little warm. After shutting off the power, I pulled the GFCI outlet out of the wall and checked all the connections (which were fine). I left it out of the wall and reconnected the 12 amp load. After several hours under continuous load I checked the temperature of the device and wires using an infrared temperature meter. Here's what I found:

Ambient temperature: 82
GFCI temperature: 86
Romex coming from electrical panel: 93
Romex between GFCI and load: 87

Both runs of Romex carry exactly the same load, although the Romex from the electrical panel is 23 year old and the Romex to the outlet is new.

Should I be concerned about the Romex running 11 degrees hotter than the ambient temperature?
 
Fred B

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Romex is listed as 60 deg C, even the old stuff. New stuff is using actual 90 deg C wire inside but still listed to 60 deg. Most devices are listed to 75Deg C. Your readings are well within the operating parameter of the wire and devices.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Kornfeld said:
I have an electric car plugged into a 15amp circuit where the car is supposed to be drawing 12 amps. The outlet is fed by gauge 14 Romex and the outlet the car is plugged into is downstream from the GFCI, also connected with gauge 14 Romex. I noticed that GFCI was getting a little warm. After shutting off the power, I pulled the GFCI outlet out of the wall and checked all the connections (which were fine). I left it out of the wall and reconnected the 12 amp load. After several hours under continuous load I checked the temperature of the device and wires using an infrared temperature meter. Here's what I found:

Ambient temperature: 82
GFCI temperature: 86
Romex coming from electrical panel: 93
Romex between GFCI and load: 87

Both runs of Romex carry exactly the same load, although the Romex from the electrical panel is 23 year old and the Romex to the outlet is new.

Should I be concerned about the Romex running 11 degrees hotter than the ambient temperature?
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Is the ambient the same at all of the locations you checked the temperature at? Also there may be more thermal lag with the older NM as it most likely has a much thicker jacket than newer NM.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
The GFCI was only 4° warmer than the ambient, nothing I would have concerns about.

In general the critical temperatures for most electrical components is significantly higher than what most people are comfortable with touching. So, if you can touch it, it is likely lower than its allowable temperature.
 
kwired

kwired

Electron manager
Location
NE Nebraska
James L said:
Those numbers in the OP are right in the sweet spot of the ambient temperature correction chart View attachment 2566873
Click to expand...
and yet his actual measured temperatures are still well below 60 or 75 deg C that the items are rated for.

60 C is 140 F some may be able to handle touching that for several seconds, some may not. Any higher and most anyone is likely to get burns from touching it.
 
James L

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
kwired said:
and yet his actual measured temperatures are still well below 60 or 75 deg C that the items are rated for.
Click to expand...
Exactly. That sweet spot (1.00 correction factor) means full load with no worries
kwired said:
60 C is 140 F some may be able to handle touching that for several seconds, some may not. Any higher and most anyone is likely to get burns from touching it.
Click to expand...
I've been in attics at 155⁰ F and had to go across ductwork. No bueno. Like walking barefoot across hot asphalt
 
kwired

kwired

Electron manager
Location
NE Nebraska
Kornfeld said:
I have an electric car plugged into a 15amp circuit where the car is supposed to be drawing 12 amps. The outlet is fed by gauge 14 Romex and the outlet the car is plugged into is downstream from the GFCI, also connected with gauge 14 Romex. I noticed that GFCI was getting a little warm. After shutting off the power, I pulled the GFCI outlet out of the wall and checked all the connections (which were fine). I left it out of the wall and reconnected the 12 amp load. After several hours under continuous load I checked the temperature of the device and wires using an infrared temperature meter. Here's what I found:

Ambient temperature: 82
GFCI temperature: 86
Romex coming from electrical panel: 93
Romex between GFCI and load: 87

Both runs of Romex carry exactly the same load, although the Romex from the electrical panel is 23 year old and the Romex to the outlet is new.

Should I be concerned about the Romex running 11 degrees hotter than the ambient temperature?
Click to expand...
Since you left the device out heat wasn't being trapped in the outlet box. That heat has to build up to higher than your body temperature before you will even be able to say it feels warm. The 86-87 degrees you measured should not feel warm to you if you touched those items. Probably won't feel cold either though just touching with your hands. But if you immersed yourself in 86 degree water it definitely will be cold to you as it will be pulling a lot of heat away from your body.
 
Joethemechanic

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
If I touched a piece of romex stapled to a stud in a garage and it was 140F, I'd be a bit nervous. I wonder how many amps it would take to get a piece of 14 there. Lets say 60F ambient
 
James L

James L

Senior Member
Location
Kansas Cty, Mo, USA
Occupation
Electrician
Joethemechanic said:
If I touched a piece of romex stapled to a stud in a garage and it was 140F, I'd be a bit nervous. I wonder how many amps it would take to get a piece of 14 there. Lets say 60F ambient
Click to expand...
The chart would say you could add 20% and stay nice and cool (18 amps)

I'd imagine with that kind of ambient temp you'd have to put 35-40 amps on it to get to 140F
 
R

rc/retired

Senior Member
Location
Bellvue, Colorado
Occupation
Master Electrician/Inspector retired
kwired said:
Since you left the device out heat wasn't being trapped in the outlet box. That heat has to build up to higher than your body temperature before you will even be able to say it feels warm. The 86-87 degrees you measured should not feel warm to you if you touched those items. Probably won't feel cold either though just touching with your hands. But if you immersed yourself in 86 degree water it definitely will be cold to you as it will be pulling a lot of heat away from your body.
Click to expand...
This is interesting. IIRC 86 degrees C is 98.6 F, and 87 C is feverish. 101? Not going to do the math right now.
Anyway, I agree on your description of heat transfer.
The example I use is, a wood floor and a carpeted floor is the same ambient temperature.
Your bare feet transfer heat faster on a wood floor than a carpeted floor.
Thus, a wood floor feels colder.

Ron
 
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