TM 5-3895-374-24-1
INTERNAL LONG TIME DELAY SELECTION
The GC-100 relay has four available long time delay settings (Curve B-0 1, Curve C-0 2, Curve D-0 3, Curve F-0 5 second
nominal). As manufactured, the relay will have its long time delay connected for 0 1 second and a jumper from terminal 15
to 16 so its 0 055 second short time delay circuit is restrained.
Internally, the long time delay can be set at the other available values as follows:
1.
Disconnect 120 Vac power to GC-100 relay. Printed circuit board has 120 Vac on it when energized.
2.
Remove cover, exposing the printed circuit board.
3.
Carefully disconnect the flexible lead from the 0 1 second slip-on terminal and connect it to the slip-on terminal
marked with the desired time delay setting.
4.
Select proper pressure sensitive label (included with this booklet) and attach to nameplate to cover the Curve B
letter designation. Use A for 0 055, C for 0 2, D for 0 3, or F for 0 5 second.
5.
Replace cover and cover screws.
SHORT TIME DELAY
During the construction phase of a project, it is recommended that all ground fault relays use the shortest available time
delay. This is the time when faults are most likely to occur and when selective coordination of mains, feeders and branch
circuits is least necessary.
With the jumper from terminals 15 to 16 temporarily disconnected, the GC-1 00 relay will have 0 055 second nominal delay
(Curve A). Replace jumper when construction is complete.
If relay is to be operated permanently with jumper 15 to 16 removed, and without restraint input wiring, attach pressure
sensitive label A to nameplate.
ZONE SELECTIVE INTERLOCKING
With this connection system, each ground fault relay controlled disconnect will open after only 0 055 second relay delay
(plus disconnect operating time) when a ground fault occurs in the zone where it is the nearest to the supply source.
However, this disconnect will be restrained to its relay’s long time delay and will open only for back-up protection if the fault
occurs in a zone supplied by a downstream ground fault relay protected disconnect. Occasionally, the upstream
disconnect will be specified to be lock-out restrained (will not be ground fault tripped) when back-up protection is not as
necessary as continuity of supply to other circuits.
The major advantage of zone selective interlocking is that arcing fault damage can be kept to a minimum by having short
time delay tripping for faults which occur between a main and feeder, or possibly between a feeder and a branch
disconnect. However, great care must be taken in wiring and testing the installation to make sure it operates as intended.
Figure 5 shows a method of obtaining three level zone selective interlocked protection. For a fault occurring at location 3
GFR No 3 trips in approximately 0 055 second and restrains GFR No 2 to a 0 2 second delay. GFR’s No 2 and No 1
provide back-up protection.
For a fault at location 2, GFR No 2 trips in approximately 0 055 second and restrains GFR No 1 to a 0.5 second time delay
for back-up protection.
For a fault at location 1, GFR No 1 trips In approximately 0 055 second. Its 0 5 second long time delay still operates as a
back-up circuit if any component of the short time delay circuit fails.
(page 3-93)
