Specifications

Operations – Ground Fault Protection
Adjustable Ground Fault Pickup and Adjustable Ground Fault Delay
17
Adjustable Ground Fault Pickup
The Ground Fault Pickup adjustment is used to set the level
of ground current at which circuit interruption will be initiated.
Together with the Ground Fault Delay, this adjustment allows
selective tripping between main and feeder or other down-
stream breakers.The available ground fault pickup settings as
a percent of the SB breaker MAX ampere rating are listed
below. In compliance with the National Electric Code (NEC
230-95), no trip point setting exceeds 1200A.
Adjustable Ground Fault Delay
The Ground Fault Delay adjustment is used to set the time
interval the breaker will wait before responding once the
ground fault pickup level has been reached.There are two
modes of operation for this adjustment for Siemens Electronic
Trip Units; one is a fixed delay and the other is 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 percent of the MAX rating.
Ground Fault Memory Circuit
Electronic Trip Units with ground fault protection come
equipped with a ground fault memory circuit.This circuit inte-
grates ground fault currents with time.This provides added
protection by preventing ground fault delay circuits from being
reset to zero when the ground fault currents are intermittent
and erratic.Time constants for the current integration are pre-
set within the unit as a function of the Ground Fault Delay.
Ground Fault Sensing Schemes
The trip unit can be configured to accommodate the following
ground fault sensing schemes:
• 3-Phase, 3-Wire Residual
• 3-Phase, 4-Wire Residual
• Source Ground
All that is required of the user to configure the trip unit to
support these protection schemes is to set the ground fault
selection switch to the desired configuration.The selection
switch is on the right side of newer version trip units and the
left side of earlier versions.The selection switch must be set
prior to the trip unit being installed in the SB breaker.
Ground Fault Delay
Ground
Fault
Delay
.5
.1
.2
.3
.4
.5
.1
.2
.3
.4
I
2
t
Fixed
MAX RATING
= 2000A
Ground
Fault
Pickup
30
20
21
22
23
24
25
26
27
28
lg=
% MAX
RATING
Secs
@1000A
MAX Rating Available Setting = %MAX Rating
400A 20 25 30 40 50 60 70 80 90 100
800A 20 25 30 40 50 60 70 80 90 100
1200A 202530405060708090100
1600A 202632384450566268 75
2000A 202327303540455055 60
2500A 20 23 26 29 32 35 38 41 44 48
3200A 20 21 23 25 27 29 31 33 35 37
4000A 202122232425262728 30
5000A – – – (SETTING FIXED AT 1200A) – – –
Fixed Ground
Fault Delay
Available Switch
Settings
(All Farme Sizes)
Adjustable Ground
Fault 1
2
t Delay
Available Switch
Settings
(All Farme Sizes)
.1
.2
.3
.4
.5
10
1
0.1
0.01
0.1 1 10 100 xl
n
Time In Seconds
0.1
10
1
0.1
0.01
110100xl
n
Time In Seconds
.5
.1
.2
.3
.4
I
2
t
Ground
Fault
Pickup
Ground Fault
Fixed Delay
Ground
Fault
Pickup
Ground Fault
l
2
t Delay
Secs
@.5 MAX
Rating