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The CURRENT RATING of a fuse is a value expressed in amperes that represents the amount of
current the fuse will allow to flow without opening.
The VOLTAGE RATING of a fuse indicates the ability of the fuse to quickly extinguish the arc
after the fuse element melts and the maximum voltage the open fuse will block.
The TIME DELAY RATING of a fuse indicates the relationship between the current through the
fuse and the time it takes for the fuse to open. The three time delay ratings for fuses are DELAY,
STANDARD, and FAST.
DELAY FUSES allow surge currents without opening. They are used to protect motors, solenoids,
and transformers.
STANDARD FUSES have neither a time delay nor a fast acting characteristic. They are used in
automobiles, lighting circuits and electrical power circuits.
FAST FUSES open very quickly with any current above the current rating of the fuse. They are used
to protect delicate instruments or semiconductor devices.
The OLD MILITARY FUSE DESIGNATION is a system of fuse identification that uses coding to
represent the current, voltage, and time-delay rating of the fuse. New fuses purchased by the Navy will no
longer use this designation.
