Totally fried wire into circuit breaker

[Mmfitzpatrick]

Thanks to this thread, I moved up my annual electrical panel and circuit breaker inspection.



After loading the generator to max (40A) by turning all the heavy AC loads, and after about 15 minutes, I take my heat gun and shoot everything.


I'm mainly interested in terminal and circuit breaker temps, especially for high load circuits.



The first pic shows the temp (91F) for the water heater circuit breaker. The second pic shows the crimped connection temp (155F). The third pic shows the wire temp (100F) about 1" before the crimped connection. Talk about highly localized heat!



What you should know is that the circuit was wired new in 2009 with 12/3 when there was a 1000 watt water heater. This was replaced in 2015 with a 1500 watt water heater, but the #12 wire should have been ok if there had not been a weakness at the crimp.


So, after replacing the crimp: 1) Going to move the inspection schedule to every 6 months, and 2) give thanks to the heat gun. Again! Great tootl!

Great post. But just a note of caution about heat guns. They are very useful, but you need to understand how they work. You are not just measuring temp at the red dot, it is the center of the cone that you are measuring.
The guns have a spec usually in degrees of Arc that they measure. So narrower Arc, better gun. Also the closer you get, the better the measurement.
So if you are measuring something close to a higher temperature, it will read higher. If you are measuring something small, like a wire, it will read lower.
Still a must have trouble shooting tool.

 

[diver dave]

Eventually all wire connections can loosen. Heat being one reason, lots of current flow another, soft metals also deform under pressure. Temp changes make metal expand and contract. It was real bad with aluminum wiring in homes, took special connection procedures and device designs, caused lots of troubles compared with copper wiring which conducts heat and current better and not as soft a metal, temp changes affect it less. Metals also get a partially insulating covering of corrosion on the surface, aluminum is bad for that, but copper can too.

If you have done a lot of wiring with romex, after you tighten the copper wires to lugs, you find that if you go back later, they may feel loose and need more tightening up. My light fixtures at home sometimes blink after many years of use, and when you check them the screws are loose. But they were tight when first put together. Could also be caused by years of incandescent bulbs which heat up light sockets. Same thing happens with marine wires. Could be fine for a long time, until it is not. With high current loads on poor connections starting to work loose bad things start to happen fast.

There is a remedy, but not available for the common circuit breaker.

https://www.wago.com/us/connection-technology

I've designed with Wago cage clamps back in the '90s for industrial applications. Instead of a "constant distance" scheme, like a screw attach; these use "constant force" springs. Like you say, cold flow, creep, will ultimately reduce the clamping force on a screw attached electrical connections, especially bad with short screws, lack of using torque wrenches and poor crimps.