Application guidelines for instantaneous-trip circuit breakers in combination motor starters

This paper addresses the application of instantaneous-trip molded-case circuit breakers (MCCB's) in combination motor starters. These circuit breakers have been widely used in many industries for motor circuit protection. If they are not properly applied, situations of false tripping on motor starting and contact welding of contactors under low-level faults may occur. Energy 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 analysis of application issues and solution options. Index Terms - Combination motor starter, instantaneous-trip molded-case circuit breaker, low-voltage protection.