scope:

This guide applies to low-voltage ac power circuit breakers of the 635 V maximum voltage class with separately-mounted current-limiting fuses for use on ac circuits with available short-circuit currents of 200 000 A (rms symmetrical) or less. Low-voltage ac fused power circuit breakers and combinations of fuses and molded-case circuit breakers are not covered by this guide.

This guide sets forth recommendations believed essential for the selection of current-limiting fuses (see NEMA FU-1¹ and UL 248-1) for use in combination with low-voltage ac power circuit breakers, rated in accordance with IEEE Std C37.13™ and applied in metal-enclosed low-voltage power circuit breaker switchgear in accordance with ANSI/IEEE Std C37.20.1™.

NOTE-The combination of a circuit breaker and separately mounted fuses is limited to 600 V based on fuse maximum voltage ratings.²

¹Information on references can be found in Clause 2.

² Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement this standard.