Wires melting at water heater thermostat

[Mandersoon]

Hey all - so I have a wire melting problem which has manifested twice now. I have replacement parts on order, but would like to know if anyone might have more insight into the problem. I have a Suburban water heater with dual source heat; electric and propane. About 6 months ago, I started smelling burning plastic, indicative of melting wires. Traced it to the AC input to the water heater thermostat. I figured it was a loose connection caused by driving, which resulted in arcing and then melting. I replaced everything and it's been working like a champ all winter. Couple days ago, I smelled the same thing, and went back to the same place to see the same result. Any idea what might cause this to happen twice now?


Couple of photos; one from the fall, one from two days ago.


Thanks!

[chuckster57]

I would be looking at the wiring from the switch..

[travelin texans]

Mine did the same. I folded that metal lip down nearly flat where wires come up & trimmed the lip on the black cover about a 1/4". The wires were being pinched by one or the other & shorting them out against the tank. Never had the problem again. Because of the tank curvature the wires running upwards were not a problem.

[flybouy]

I think Danny nailed it. When I blow those pictures up I can see a horizontal line at the lip on the lower black wire where it burned, on the other picture I can see a horizontal line that's been pinched in the same area on the black wire for the terminal above.