TM 5-3895-374-24-1
RELAY SETTINGS
The GC-100 Ground Fault Relay has adjustable trip settings of 100 to 1,200 amperes RMS. Figure 6 shows the five delay
curves available. To allow time for fault clearing, the minimum recommended difference in time delays between any two
GFRs is 0.1 second. If a ground fault protected bolted pressure contact switch is used downstream from any ground fault
protected device, the minimum time delay difference should be 0.2 second.
FIGURE 6
High trip settings on main and feeder circuits are desirable to avoid nuisance tripping. High settings usually do not reduce
the effectiveness of the protection If the ground path Impedance is reasonably low. Ground faults usually quickly reach a
value of 40% or more of the available short circuit current in the ground path circuit.
COORDINATION WITH DOWNSTREAM CIRCUIT BREAKERS
It is recommended that the magnetic trips of any downstream circuit breakers which are not equipped with ground fault
protection be set as low as possible.
Likewise, the ground fault relay trip settings for main or feeder circuits should be higher than the magnetic trip settings for
unprotected downstream breakers where possible. This will minimize nuisance tripping of the main or feeder breaker for
ground faults occurring on downstream circuits.
(page 3-95)
