Design guidelines for safer low-voltage distribution systems Part II: Motor circuits

This paper continues investigations of the concept of maximum low voltage circuit breaker ratings that facilitate fast tripping for arcing faults with a selectively coordinated system. Motor loads are the focal point of the report. Guidelines are provided for maximum motor horsepower ratings that should be used depending on the kVA rating of the suppy-side transformer. Using the guidelines should prevent a situation from occurring where the coordinated main circuit breaker short time and instantanesous settings are not sensitive enough to detect main bus arcing currents, and dangerous levels of arc incident energy are possible.