16
2.9.2 MECHANICAL JAM
Overloads will normally cause a trip according to the overload
curves of fig. 3-2. In some situations it may be desirable to pro-
tect associated mechanical equipment against a jam while runn-
ing. Setting switch S303 off will cause the relay to trip whenever
the current rises above 3 times the FULL LOAD—AMPS con-
trol setting for one second while the motor is running
The Protect 4A automatically defeats mechanical jam during
the high starting inrush current but enables this option (if switch
S303 is off) as soon as the inrush current drops below the FULL
LOAD AMPS setting. This feature is especially useful in appli-
cations such as pumps and fans where overloads are not part
of normal operation. Mechanical jam will activate the overload
indicator.
2.9.3 GROUND FAULT INDICATION ONLY
In some resistance grounded systems a single ground fault
detector is used to monitor a complete bus feeding numerous
motors. If one of the motors develops a ground fault, an alarm
condition is registered on the central ground fault monitor but
the motors may be allowed to continue running to prevent a
production shut down. This is possible since the ground fault
current is resistance limited, however the faulty motor should
be repaired as soon as possible because a second ground fault
on another phase could cause a phase to phase short circuit
resulting in extensive damage. If the motors don’t have indi-
vidual ground fault protection, the whole bus must be sched-
uled for a convenient shutdown and each motor checked until
the faulty one is found.
A ground fault above the trip settings will normally cause the
Protect 4A to trip with a ground fault indication. Setting switch
S304 off will cause the ground fault indicator to activate but will
inhibit a trip due to a ground fault. If each motor is equipped
with a Protect 4A and this feature is selected, when the central
monitor registers a ground fault, it is only necessary to look at
each Protect 4A to locate the faulty motor. The defective motor
can then be shut down and repaired when convenient without
shutting down the rest of the bus and testing every motor.
Summary of Contents for PROTECT 4A-120
Page 1: ...MOTOR PROTECTION RELAY INSTRUCTION MANUAL ...
Page 5: ...2 FIGURE1 1 PROTECT 4A TYPICAL SYSTEM CONNECTION ...
Page 11: ...8 FIGURE 2 2 PHASE CT DIMENSIONS FIGURE 2 3 GROUND FAULT CT DIMENSIONS ...
Page 21: ...18 FIGURE 3 1 FRONT PANEL LAYOUT ...
Page 35: ...32 FIGURE 4 1 SINGLE PHASE INJECTION TESTING FIGURE 4 2 100 AMP CURRENT SOURCE ...
Page 39: ...36 FIGURE 4 3 GROUND FAULT EARTH LEAKAGE TEST ...
Page 44: ...41 FIGURE 5 1 HARDWARE BLOCK DIAGRAM ...
