Overcurrent Protection Configuration
27
5.5
Instantaneous Fault Protection
The instantaneous pickup sets the level of high current at
which the trip unit will trip the circuit breaker without a time
delay. Non-delayed tripping, in response to a severe overcur-
rent condition, minimizes potential damage to electrical sys-
tems and equipment. The instantaneous pickup may be set to
a range of continuous current values depending on the breaker
rating. The pickup is independent of the long time setting.
To select instantaneous fault protection, from the
Protective
Menu
, select
Instantaneous
and press Enter
. The following
screen appears:
The pickup value is the only value to set. To program this value,
press the Up
or Down
Arrow key until the scale shows
the desired value. When displayed, press Escape
then
Enter
to accept this setting.
5.6
Ground Fault Protection
Trip units equipped with the protective ground fault option can
be configured to accommodate the following ground fault
sensing schemes:
•
Residual
•
Ground Return
To configure the trip unit to support these protection schemes,
the user is required only to set the ground fault selection switch to
the desired configuration. The selection switch is on the top right
side of the trip unit and must be set prior to the installation of the
trip unit in the circuit breaker. Refer to
Chapter 2, Installation
.
Two values must be set to provide the ground fault protection:
the Pickup value and the Delay value. The pickup value is used
to set the level of ground current at which circuit interruption
will be initiated. Together with the delay value, this setting
allows selective tripping between main and feeder or other
down-stream breakers. In compliance with the National Electric
Code (NEC 230-95), no trip point setting exceeds 1200A. A
complete listing of the available ground fault pickup settings is
given in a table in Appendix,
Parameter Settings
.
To select ground fault protection, from the
Protective Menu
select
Ground Fault
and press Enter
. The following screen
appears:
To program the pickup first make sure the Pickup scale is
selected, pressing Enter
as necessary to move the highlight
to the Pickup parameter. Then press the Up
or Down
Arrow key until the scale shows the desired value. When dis-
played, press Enter
to move to the delay parameter, or
press Escape
to accept these settings.
The Ground Fault Delay value is used to set the time interval
the breaker will wait before responding once the ground fault
pickup level has been reached. This setting has two modes of
operation: a fixed delay, and an inverse I
2
t ramp delay.
In the fixed delay mode, the Ground Fault Delay may be set to
0.1, 0.2, 0.3, 0.4, or 0.5 seconds. In the inverse I
2
t ramp delay
mode, the delay may be set to a calibrated value of 0.1, 0.2,
0.3, 0.4, or 0.5 seconds at a current equal to 0.5 times the MAX
RATING. The inverse I
2
t ramp delay reverts to a fixed delay of
the same value when the ground current (I
g
) exceeds 50 per-
cent of the MAX RATING.
10
1
0.1
T
ime (Seconds)
Current (Amperes)
Instantaneous
10
1
0.1
T
ime (Seconds)
Current (Amperes)
Ground Fault
