Trip Devices
Continued
High Range Instantaneous
Ground Fault Pickup and
Ground Fault Delay
(Optional)
The ground fault pickup
adjustment controls the level
of ground fault current at
which circuit interruption will
occur. To comply with the
1 981 National Electrical
Code (NEC 230-95), no
trip point exceeds 1 200
amperes. The common
square knee of the curve
can be replaced with an l2t
function to facilitate coordi
nation with downstream
devices such as thermal
magnetic breakers and
fuses whose time-current
curves do not easily relate to
the square-shape sensing
characteristics common to
solid state trip devices.
Memory Circuit
Because of the highly inter
mittent and erratic nature of
arcing ground faults, a mem
ory circuit has been incorpo
rated in all MicroVersaTrip
ground fault sensing circuits
as standard. The memory
circuit integrates arcing fault
current with time, essentially
summing the intermittent
ground current spikes. In the
20
Includes adjustable short
time pickup, adjustable
short-time delay and a high
level instantaneous setting
is adjustable in four steps
from 40 to 1 00 percent of
the circuit breaker frame
The ground fault delay
adjustment is used to add a
pre-determined delay in time
to the trip point once the
ground fault pickup level has
been reached. This provides
tripping selectivity between
main and feeder or other
downstream breakers.
The ground fault unit also
includes as standard an
inverse 12t ramp to substan
tially improve coordination
with downstream protective
devices such as fuses and
thermal magnetic circuit
breakers.
diagrams, it can be seen
how the memory function
works.
Diagram
A
shows a typical
ground fault with half-cycles,
whole cycles and multiple
cycles missing, as normally
occurs.
Diagram B
shows trip
response of a typical ground
fault function which does not
include memory. The
short-time rating permitting
maximum use of the
breaker's short-time capa
bility. This high level instan
taneous function increases
system protection without
losing selectivity.
GROUND FAULT PICKUP
.35 .355
.. 255
®
.45
25
�
.455
OFF
.55
.65
GROUND FAULT
PICKUP
GROUND FAULT DELAY
12T IN
12T OUT
MAX MAX
GROUND FAULT
DELAY
breaker never trips because
the time delay circuits are
reset with every missing
cycle.
Diagram C
shows response
@
of Micro Versa Trip ground
B
fault circuits to the same
ground fault; the circuit's
memory carries through the
©
missing cycles and gener-
ates a trip Signal after the
With Memocy
preset time delay.
www . ElectricalPartManuals
. com
www
. ElectricalPartManuals
. com
