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The purpose of the Joslyn AC Surge Protector, P/N 1457-40, is to provide voltage clamping
whenever the instantaneous (surge) line-to-neutral voltage exceeds a level of approximately 500
volts peak. The protector responds in nanoseconds, and automatically restores itself to normal
condition after termination of the surge condition. No power-follow occurs and the disturbance
to the line voltage is minimal.
Each phase of the protector consists of two protector modules (one connected to neutral and one
to ground), a fuse, and two monitoring circuits. Two additional modules are connected between
neutral and ground. Refer to connection diagram of Figure 2.
Each protector module consists of several metal oxide varistors (MOVs) in parallel. Each MOV
has its own fuse. The fuse will blow before the maximum surge current rating of the MOV is
exceeded. The fuses also help to balance the current distribution among the MOVs.
A replaceable fuse is provided for each phase to disconnect the protector module from the power
source in the event of a continued overvoltage or excessive surge current. The fuse may be blown
by surge currents exceeding 28,000 amperes. The fuse can be removed to disconnect the
protector from the line for test purposes without having to turn off the power to the equipment
the protector is protecting. In addition to the replaceable fuse, each protector module is internally
fused in case of failure of the clamping components in a shorted mode.
Each phase of the protector has a monitoring circuit with an indicator light on the cover of the
protector enclosure. When the protector is in operating condition the light is on. No monitoring
is provided for the neutral-ground modules.
MAG/MNL145740(A)
III. THEORY OF OPERATION
Joslyn P/N 1457-40
AC Surge Protector
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