Burnt out main breaker requires refurbishment of buss work and main breaker replacement

A 100 amp main breaker in a residential panelboard overheated and burnt out requiring replacement of the breaker and panel buss.

The breakers are manufactured using a common design type where the breaker contacts slip over protruding ends of the panel’s buss assembly to facilitate a mechanical and electrical connection. This design helps secure the breaker in place and provides the flexibility required to use one panel with different rated breakers. The contact surfaces are small and susceptible to overheating if the contacts are misaligned while fully loaded to their rating.

A high electrical load was placed on the main breaker and arcing occurred at the contact points between the main breaker and the panel buss.

- The panel was a 125 amp maximum, 120/240 volt 1 phase combination panel. The main breaker was rated for 100 amperes (amp)
- The panel supplies a regular house load as well as an AC unit, pool heater and crawlspace heater. This load would be close to the maximum breaker rating of 100 amp.
- The 100 amp main breaker and panel buss showed signs of overheating, pitting and arcing.
- The breaker contact surface and the panel buss mating surface overheated and burned out the breaker which cut (interrupted) the power supply to the residence.
- The main breaker and panel buss were misaligned and did not provide full contact between the two points. This produced gaps between the two contact points.