Two basic families of fuses are current limiting and noncurrent limiting.
The current-limiting fuse melts and extinguishes the arc in a half-cycle or
less. The noncurrent-limiting type may melt in less than a half-cycle when
subjected to very high values of short-circuit current, but is unable to
extinguish the arc in a half-cycle. Since the arc is a fl exible conductor, the
noncurrent-limiting-type fuse will allow the short-circuit current to reach its
maximum peak value. The current-limiting type of fuses are constructed with
mechanisms to extinguish the arc, thereby preventing the short-circuit current
from reaching its maximum peak value. The fuses are used in conjunction
with circuit breakers, motor starters, disconnect switches, and the like to
provide protection similar to the circuit breaker overcurrent trip devices.
However, fuses have fi xed time–current relationships and therefore do not
provide the same fl exibility as the overcurrent relationships and therefore do
not provide the same fl exibility as the overcurrent trip devices. Fuses cannot
open and close a circuit by themselves. They must be combined with some
supplementary device, such as a disconnect switch, a circuit breaker, or a
contactor. Fuses can be divided into medium- and low-voltage fuses