scope:

This specification covers instrument type fuses designed for the protection of electrical, electronic, and communication equipment on direct current (dc) and alternating current (ac) (up to 400 hertz (Hz)) circuits.

The type designation of fuses is in the following form and as specified (see 3.1 and 6.2).

The style is identified by the letters "FM" followed by a two-digit number denoting a fuse of a given construction and dimensions.

The characteristic is identified by a one-letter symbol which indicates the relative overload interrupt time (see 6.5) in accordance with table I. TABLE I. Characteristics.

Symbol Relative overload interrupt time ---------------------------------------------------------------------------- A Normal B Time delay

Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Defense Supply Center, Columbus, ATTN: DSCC-VAR 3990 East Broad Street, Columbus, OH 43213-1199, by using the Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter.

The voltage rating is the maximum dc or ac root mean square (rms) voltage for which a fuse is designed (see 3.1). The voltage rating is identified by a numerical value followed by the letter "V".

The current rating is the amount of current a fuse will carry indefinitely without interruption (see 3.1). The current rating in amperes and fractions of an ampere is identified by a numerical value followed by the letter "A".

When specified, a suffix letter shall be added to the type designation covered by selected specification sheets to denote optional finish (see 3.1).

intended Use: