Application guidelines for instantaneous trip circuit breakers in combination motor starters

This paper addresses the application of instantaneous trip, molded-case circuit breakers in combination with motor starters. These circuit breakers have been used widely in many industries for motor circuit protection. If not properly applied, situations of false tripping on motor starting and contact welding of contactors under low level faults may occur. High efficiency motors compound the issue of false tripping on motor starting. This paper discusses the components of combination starters, reviews testing requirements and provides examples of coordination with an analysis of application issues and solution options.