TM 5-3895-374-24-1
When a ground fault occurs, current flows from the Sensor through TR whose output voltage is proportional to the fault
magnitude and the adjustment of the Trip Setting Potentiometer. The Pick Up Circuit rectifies and senses this voltage.
When the voltage reaches the pick up value, the Pick Up Circuit activates both the Dual Time Delay and the Restraint
Output Circuits.
The Dual Time Delay Circuit contains one short delay (Curve A) and one long delay, both timing simultaneously unless
there is a restraint input. When either circuit times out, the Control Triac Circuit turns "on" and operates Output Relay K
which energizes the Disconnect Trip Coil. A contact latches the relay "on" providing a continuous indication of ground fault
tripping by lighting lamp L2 The Ground Fault Relay is reset by pressing the Reset button interrupting the power source
momentarily. A ground fault lasting for less than the time delay period will not pick up the Disconnect Trip Coil, thus
eliminating nuisance tripping on self-clearing faults.
The Restraint Output Circuit has a voltage output whenever the ground fault current exceeds the pick up point. This output
may be connected to either a Lockout Restraint or a Restraint to Time Delay Input of another GC-100 Ground Fault Relay.
All GC-100 relays using restraint Interconnections must have a common ground. The Restraint Common (terminal18) is
internally connected to terminal 19 for wiring convenience. Do not ground the Restraint Output (terminal 15).
Restraint to Time Delay Input (terminal 16) when energized, blocks only the short time delay permitting operation of the
long time delay of 0.1, 0.2, 0.3 or 0.5 seconds nominal depending on the internal time delay selection connection. Lockout
Restraint Input (terminal 17) when energized, blocks both time delay circuits, restraining the relay from tripping under any
ground fault condition. When restrained, a relay continues to generate a restraint output signal if the fault current exceeds
the pick up level, so restraint signals can be sent further upstream If desired.
In single relay applications or when zone selective interlocking Is not used, allowing a GC-100 to restrain itself makes all
five time delays available on each relay Connections for this application should be made as shown in Figure 2
(page 3-90)
