Problem solved. It was breaker issue. All the breakers I was swapping with, I tried 2 or 3, had the same date code on them. I tried one with a different code and it holds no problem. It seems that the one batch has a low trip curve.
My theory side was trying to figure out how something on the circuit could cause this when I was measuring only 12.5 amp at the breaker. I couldn't understand how it could be anything but the breaker.
The code on the breakers appears to indicate 1992 which is about right for when the panel was installed.
Just an FYI the heater in question had a rating of 120 volts 1350 watts. Should not be a problem on any 15 amp circuit.
Last edited by jdevlin; 01/23/10 07:37 PM.
