Total Motor Branch Circuit Protection with Instantaneous Trip Type Circuit Breakers and High Fault Circuit Protectors (HFCP)

Abstract

Instantaneous trip type circuit breakers can protect controllers against damage due to overcurrents above six and up to 13 times full load motor currents (FLMC). They may be used for full protection if the starter and wire are self-protected up to 13 times FLMC. Molded case circuit breakers take at least 1/2 to 1 cycle to interrupt. An interrupting time of 1 cycle is too long at high let-through currents to protect contactors from being damaged and, in many cases, to protect heaters from being burned out. A line of high fault circuit protectors is described that protect all branch circuit components in case the available short circuit current is so high that the let-through current would, without protectors, be higher than a current that the branch circuit elements could with-stand for at least 1 cycle. A system is described that insures tripping of the circuit breaker whenever a high fault circuit protector opens. Tests, physical arrangements, coordinated system selections, and applications are described.