Characteristics, selection guidelines and performance of circuit protection devices for ASDs

The goal of all circuit protection devices is to mitigate and minimize collateral damage when a failure occurs to either the source (ac line) or the equipment. The circuit protection device is often given little attention, that is until erroneous trips hamper performance or unexpectant damage occurs within the equipment. Then the devices are often reviewed for performance characteristics and operating conditions. To meet this need various devices have been designed for this purpose and various standards have been written to provide guidance for the usage of those devices. The focus of this paper will be on the interplay between drive short-circuit current rating (SCCR) and protective device sizing as well as the scaling of such systems, ie should a fuse sized for a 10A circuit have the same guidelines as one used for 1000A. This paper will review how UL 508A, 508C, and the National Electric Code impacts Adjustable Speed Drive (ASD) protection requirements. This paper evaluates a test setup scheme to measure fuse performance. The peak current and I²t test results with both test schemes from three protection devices, a Time Delay (TD) Class J fuse along with two Non Time Delay (NTD) Class J and T fuses, are presented and explained. A novel method of comparing the results is offered by viewing the collateral damage associated with a failure. This methodology has minor impact at low power ratings, but major implications with high power ratings, where equipment is often field repairable.