Power+™ Trip Units
Short-Time Delay
Short-time delay is a lways provided when short-time pickup
is ordered. Short-time delay provides additional refinement in
providing coordination between upstream and downstrea m
protective devices. There a re three time delay bands that
provide delays from 100 ms to 350 ms of 1 ( M IN). 2 (I NT). 3
(MAX).
Short-time delay with l2t OUT
Selectable Short-time l2t Function
Selectable short-time l2t is always provided with the short
time option. The l2t helps the solid-state trip unit coordinate
with downstream thermal magnetic devices or fuses. This
function impacts the shape of short-time and short-time
delay time current curves, and may be programmed either IN
or OUT.
Short-time delay with l2t
IN
Normal Ground-Fault Protection (Optional)
G round-Fault Protection
The ground-fault function in the Power+™ trip unit is field up
gradeable. It is enabled and adjusted through the rating plug.
To upgrade to the ground-fault option, simply remove the
non-ground fault rating plug that does not have the ground
fault option and install a g round-fault rating plug. A ground
fault is an unintentional current fiow from a circuit through
a conductive path to ground. Ground faults usually have
intermittent or very low values of current fiow, as depicted in
G raph A . and are not detected by long-time overload protec
tion.
12
Some ground-fault trip systems may not detect this type
of fault because the intermittent nature of the fault never
exceeds the trip threshold as illustrated in G raph B.
The Power+ trip unit detects and integrates (adds a series of
a rcing and intermittent current pulses) the low-level cur
rent of a ground fault. This integration function provides a
memory response for g round fau lts to achieve preferred
g round-fault protection as shown in Graph C.
Fault Current
Ground Fault
�!!e_c!�!'
...................
_
.......................
_
Ground-fault memory circuit
The NEC requires that the maximum g round-fault setting not
exceed 1200 amps. G round-fault protection includes pickup
setting, ground-fault delay settings and selecta b le 12t func
tion.
G round-fault pick-up settings are based on multiples of S ,
the current sensor rating. The lowest setting is 2 0 % o f S, and
the highest setting is based on current sensor a m p ratings,
such that the maximum setting does not exceed 1200 amps.
There a re three ground-fault delay bands of 1 (M IN). 2 (I NT). 3
( MAX) ranging from 100 ms to 350 ms. The l2t function adds
an 12t slope to the square corner of the ground-fault time
current curve transition, from pickup to the constant delay
bands, to improve coordination with downstream devices.
(xS)
.24 .26
.20
Grou nd-fault pickup and g round fault time delay
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