- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
I saw this on YouTube and thought that it was interesting. I would have expected the point where all of the cables entered the panel to have the highest temperature.
NM Derating Video
- Thread starter infinity
- Start date
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
!00 amps of load at 240.
So, we are screwed by the equipment manufacturers. Inadequate testing of breakers and panels. Instead, they blame the wire, or the electrician or anyone but themselves.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I'm not seeing any bundling in the video, so it seems off the mark.
A real stress test would be to cable tie all 16 cables together into a single bundle for say 10', with a thermocouple in the middle of the bundle, and then encase that bundle in 3" of spray foam on all sides, and run the test in 30C ambient until a steady state temperature is achieved.
Cheers, Wayne
A real stress test would be to cable tie all 16 cables together into a single bundle for say 10', with a thermocouple in the middle of the bundle, and then encase that bundle in 3" of spray foam on all sides, and run the test in 30C ambient until a steady state temperature is achieved.
Cheers, Wayne
- Location
- New Jersey
- Occupation
- Journeyman Electrician (retired)
I agree it could definitely be better but you would think that the point where all of the cables enter the panel the temperature would be much higher which IMO was the message they are trying to convey.
- Location
- Illinois
- Occupation
- retired electrician
The breaker temperature has nothing to do with ampacity adjustment. The heat is simply the I²R losses in the breakers thermal element....remember that is how a thermal magnetic breaker works, the element heats until the bi-metallic bends and trips the breaker.
Joethemechanic
Senior Member
- Location
- Hazleton Pa
- Occupation
- Electro-Mechanical Technician. Industrial machinery
I'd like to see one about hot and neutral (or whatever combo of phases) entering the boxes through different knockouts. I used to see it done all the time on K&T. I've never seen any evidence of it causing a problem
- Location
- Illinois
- Occupation
- retired electrician
There is no issue until the current is 300 to 400 amps and even then, just through a ferrous metal enclosure wall is not going to be a real world issue...running the conductors separately through ferrous metal raceways for any distance is likely to result in significant heating.
Joethemechanic
Senior Member
- Location
- Hazleton Pa
- Occupation
- Electro-Mechanical Technician. Industrial machinery
From studying theory in high school in the mid 70's I always knew it was possible, but living in the real world seeing old installations, and field repairs done to electrical machinery, Seems like it's mostly overblown
Birken Vogt
Senior Member
- Location
- Grass Valley, Ca
I've seen it before on an off grid installation, the battery cables were run through different KOs "because it's DC" but there was also a really high ripple current on the cables, so much that it would show 300 amps AC and 300 amps DC on a clamp meter, or something like that. The panels of the gutter sounded like they were about to jump off the wall when current was high.
- Location
- Illinois
- Occupation
- retired electrician
In the Canadian code, rules for this issue do not even apply below 200 amps.
pipe_bender
Senior Member
- Location
- Boston
- Occupation
- Electrician
Whatever K&T they used here pre-ww2 in homes was really good hi-temp rubber, I removed two identical old 3 lamp fixtures from a kitchen, the kind grandma has 150 watt bulbs in, they were on the same switch. One was on the original K&T, non grounded, the other was on NM, the NM turned to dust and literally fell off while i removed the fixture.
The K&T was fine, I wish my rubber tires lasted that long.