Thermal Activation of Molded Case Circuit Breakers by External Heat Exposure

Yannick Alexis
Daniel Gottuk
Jensen Hughes
Baltimore MD USA
Christopher B. Wood
FireLink LLC
Tewksbury MA USA

Presented at the International Symposium on Fire Investigation Science and Technology, 2018


This paper explores thermally induced activation of Molded Case Circuit Breakers (MCCBs) that are commonly found in residential, small office and commercial occupancies. A total of 81 MCCBs were put into an oven with no current (i.e. no-load), along with thermocouples that were connected to a data acquisition system to track trip status and air temperatures proximate to the breakers. Different types of MCCBs were tested and results tabulated based on the brand, number of poles, and amperage ratings of the breakers. All the MCCBs were activated thermally during the testing, and the trip temperatures of the different types of MCCBs are displayed graphically. The breakers tended to trip between 350°F (177°C) and 470°F (243°C) and between 16 to 22 minutes from when the oven reached 160°F (the MCCB’s maximum operating temperature) and then followed a linear temperature increase of 10°F/min (5.6°C/min). The changes in the breakers’ physical conditions were also noted. This experiment provides further evidence that thermal activation of circuit breakers exposed to fire conditions may be a consideration for the investigator of a fire. Recommendations for future work are also included.

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