Temperature Sensitivity of Residential Molded Case Circuit Breakers

The experimental results are presented for minimum trip current as a function of temperature for residential circuit breakers. These are often installed in enclosures that are exposed to seasonal temperature extremes. The trip current of these thermally actuated breakers is inversely related to temperature. The relationship is shown to be linear and it varies as much as 2:1 between brands. The trip current at extremely high and low temperatures can be estimated. At low outside ambient temperature the worst case 15 A breakers will not trip at 25 A, which would be the current load of two 1500 W portable heaters plugged into the same 15 A circuit. The diminished overcurrent protection at low temperature may be a factor that contributes to the elevated incidence of residential electrical fires during winter months.