I.B. 29C891B
Page 33
Effective 11/98
To protect against the the cyclical ground fault condition
just described, all OPTIM Trip Units with ground fault
protection are provided with a ground fault memory
function. The time above pickup is retained in memory
and decays slowly. If another ground fault, high enough
to cause pickup, occurs before the time in memory total-
ly decays, the new time adds to the memorized time. It
is this cumulative time that determines whether the cir-
cuit breaker will or will not trip on these types of cyclical
ground fault conditions.
3-2.8 TIME-CURRENT CURVES
The specific time-current curves applicable to all Digitrip
OPTIM Trip Units are identified in Appendix A, Table
A.1
. Contact Cutler-Hammer for a specific curve.
3-3 SYSTEM MONITORING
Digitrip OPTIM Trip Units provide an electrical distribution
system with superior programmable protection and coor-
dination along with advanced warning capabilities, sys-
tem diagnostics, monitoring and communications. A sig-
nificant part of Digitrip OPTIM’s effectiveness is a result of
its system monitoring capabilities. A comprehensive list of
TIME
CURRENT
Note: Ground Fault Delay
represented by
dotted lines
Figure 3-17 Typical Ground Fault Time Delay
Adjustment, (I
2
t) Response
TIME
CURRENT
Note: Ground Fault Delay
represented by
dotted lines
Figure 3-16 Typical Ground Fault Time Delay
Adjustment, Flat Response
TIME
CURRENT
Note: Ground Fault Pickup
represented by
dotted lines
Figure 3-15 Typical Ground Fault Pickup Adjustment
Summary of Contents for Digitrip OPTIM 1050
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