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Op erations- Short Time Faul t Protection
Adjustable Short Time Pickup and Adjustable Short Time Delay
3.5
3
2
Short
Time
5
Pickup
xl,
. 2
8
7
Fixed
.3
Short
Time
.1
.1
Delay
.2
Sees
@8x I,
.3
Ft
Adjustable Short Time Pickup
The Short Time Pickup adjustment is used to set the level
of high current the breaker will carry for a short period of
time without tripping. This adjustment, together with the
Short Time Delay, allows downstream breakers time to
clear short circuit faults without tripping the upstream
breakers. On Siemens Electronic Trip Units, the Short Time
Pickup may be set to 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, or 8 times l
1000
100
({)
u
c
10
0
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u
<J)
E
f'=
. 1
. 01
5
8
7
Short Time Pickup
30
10
100
xl r
Swrtch S
t
n
Available
et
i
gs
Adjustable Short Time Delay
The Short Time Delay adjustment is used to set the time
interval the breaker will wait before responding to the
current value selected on the Short Time Pickup adjust
ment. There are two modes of operation of this adjustment
on all Siemens Electronic Trip Units; one is a fixed delay, the
other is an inverse l2t ramp delay. The 12t Delay has the
characteristic of being i nversely proportional to the square
of the magnitude of the overcurrent condition. This means
that higher overcurrent conditions have shorter delays and
conversely lower overcurrent conditions have longer de
lays. This characteristic allows for better coordination
with downstream circuit breakers and fuses. I n the fixed
delay mode, the Short Time Delay may be set to .07, . 1 ,
. 1 5, .2, o r . 3 seconds. I n the inverse 12t ramp Short Time
Delay mode, the delay may be set to a calibrated value of
.07, . 1 , . 1 5 , .2, or . 3 seconds at a current equal to 8 times lr.
1 000
;;;
·
100
r
i'
�
§
1 0
'!2
F
01
i'
8
10
�
E
Q)
F
Short Time Delay
xlr
Short Time
Fixed Delay
1
Available
Switch Settings
(All Frame Srzes)
xlr
Short Time
12t Delay
xlr
.3
.2
l't
Available
Switch Settrngs
(All Frame Sizes)
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