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3.
The ground fault detection pickup level with an action
of trip may also be selected using the rotary switch.
With detect and trip selection, this set is labeled
"Trip" . If a ground fault causes the circuit breaker to
trip, the "GND" indicator will blink and the "Ground
Fault Trip" message will be displayed when auxiliary
power is present.
N
ote:
Your application may require ground fault
protection. Please consider NEC and/or applicable
codes to determine required mode of operation
("OFF" , "Alarm" , or "Trip")
4.4.2 Ground Fault Time
The PT trip unit provides selection for two different
ground fault slopes: a fixed time (flat) or I
slope should be chosen to match selective coordination
needs. The I
t response provides a longer time delay
2
for current below 0.625 x In than the fixed time (flat)
response.
The time delay and slope are selected on a corresponding
rotary switch. The I
t response time selections are
2
indicated with an asterisk (*) while the fixed time (flat)
response time selections are indicated without an
asterisk. Both have a range from 0.1 seconds to 0.5
seconds. An external current sensor is required when a
3-pole circuit breaker performs ground current sensing.
The ground pickup current is a multiple of the
•
corresponding current when the rated current is less
than 1200A.
The ground pickup current is a multiple of 1200
•
(maximum by NEC) when the rated current is greater
than or equal to 1200A.
4.4.3 Ground Fault Thermal Memory
In addition to standard ground fault protection, the PT trip
unit also has a ground fault memory function that serves
to protect loads in the event of a sputtering arc to ground.
Without this function, the ground fault protection timer
resets each time the arc goes out, so that a sputtering
fault may not trip the circuit breaker. With the ground
fault memory function, the trip unit "remembers" the
sputtering ground current. The memory decays with time,
the time interval equals 6.25 times the ground fault time.
For example, with a 0.4 second setting, the function will
reset in 2.5 seconds.
The thermal memory function can be enabled or disabled
on PT10 using the PTM software.
4.4.4 Ground Fault Relay
If the Ground Fault Alarm option is selected on the LSIG
style trip unit, a red ground Alarm indicator will illuminate
to show the presence of ground current in excess of the
Ground Alarm setting.
You must then push the "RESET" button in order to reset
the relay contact.
PT 10 TrIP UnIT User ManUal Power TrIP (PT) UnITs MN013021EN January 2024 www.eaton.com
4.5 Ground Fault Sensing
The PT 10 trip unit provides for three modes of sensing
to detect ground fault currents: Residual, Source Ground,
and Zero Sequence. The ground sensing mode (Residual
or Source/Zero Sequence) is selected using the display
and navigation buttons or by using the PTM software.
Neutral protection is provided independent of the Ground
Fault function.
4.5.1 Ground Current Sensing
Ground current sensing is the standard mode of ground
fault sensing for PT units. This mode uses one current
sensor on each phase conductor and one on the neutral
for a four-wire system. This mode of sensing sums the
t response. The
2
outputs of the three or four individual current sensors.
If the sum is zero, then no ground fault exists. Residual
ground fault sensing features are adaptable to main and
feeder circuit breaker applications. If an external neutral
sensor is used with reverse feed breaker applications, the
proper polarity of the neutral needs to be considered.
4.5.2 Source Ground Sensing
The ground return method is usually applied when ground
fault protection is desired only on the main circuit breaker
in a simple radial system. This method is also applicable
to double-ended systems where a mid-point grounding
electrode is employed.
For this mode of sensing, a single 400 A current sensor
mounted on the equipment-bonding jumper will directly
measure the total ground current flowing in the grounding
conductor. Setting the ground fault type will enable this
protection. Refer to Table 5 for sensor style number.
4.5.3 Zero Sequence Sensing
Zero Sequence sensing, also referred to as vectorial
summation, is applicable to mains, feeders, and special
schemes involving zone protection.
4.6 High Instantaneous
The PT trip unit provides a high instantaneous trip
function that will trip the circuit breaker at the withstand
rating of the circuit breaker frame. This function is factory
set within the frame module and reacts to the peak
current level. It is always active regardless of the user's
instantaneous adjustment selection, including "OFF" . The
instantaneous ("INST") indicator shows this cause of trip.
4. PT Protection Settings
7
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