GE EntelliGuard G Application Manual page 20

Section 3. EntelliGuard TU Trip Unit System
Making Current Release (MCR)
This form of Instantaneous protection is provided
on all EntelliGuard G circuit breakers. This function
provides protection in case the circuit breaker is
closed on an unusually high current. A circuit breaker
that experiences 15 times (15x) or more its plug rating
is possibly closing in on a fault caused by incorrectly
wired conductors, forgotten grounding cables or
some other type of unusual low impedance fault.
Alternatively, it is closing on a very low impedance
arcing fault. In either case, there is a possibility that
equipment may be damaged by the high fault
current or an arc flash hazard has been inadvertently
created. The Making Current Release (MCR) provides
very fast protection when the circuit breaker is
closed and for the first 6 cycles thereafter. After the
6 cycles have elapsed, the Making Current Release
(MCR) is turned off and the circuit breaker reverts
to its adjustable Instantaneous pick up and HSIOC
if provided.
The Making Current Release (MCR) will clear fault
current in 40 milliseconds or less.
Reduced Energy Let-Through (RELT)
Instantaneous Trip
The EntelliGuard TU trip unit provides an optional
second, user-adjustable, RELT Instantaneous trip.
This trip provides an alternate Instantaneous setting
that allows a user to temporarily set a circuit breaker
to a more sensitive pick up to provide better pro-
tection, only when better protection is needed and
some selectivity may be sacrificed. The RELT pick
up is adjustable from 1.5X to 15X of plug rating,
independently of the normal adjustable selective
Instantaneous. It may be set higher or lower than
the selective Instantaneous.
The user must make two entries at the trip unit: (1)
Pickup settings (1.5-15X of the plug) and (2) ON, OFF
or REMOTE. ON/OFF enables or disables the pickup
setting. REMOTE allows the RELT Instantaneous
pick up to be enabled via application of 24vdc or ac
at the RELT input terminals or serial communications
via the Modbus or Profibus communication port. The
RELT pickup may be enabled via serial communica-
tion or remote 24v signal, but both need to be
indicating "OFF" for the RELT Instantaneous pick
up to be disabled. The RELT input command may
be wired to a manual switch, automatic sensor or,
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via external logic, to one or more signal sources.
When the EntelliGuard TU trip unit has the RELT
Instantaneous pick up enabled, the trip unit pro-
vides a feedback signal via an optically isolated dry
contact and serial communication. This provides
positive feedback that the trip unit has received
and reacted to the RELT Enable command.
The EntelliGuard TU trip unit's RELT capability pro-
vides the ultimate in user flexibility for wiring and
controlling an alternate Instantaneous setting for
temporary use to reduce personnel hazard. The
RELT Instantaneous pick up clears fault current in
42 milliseconds or less.
RELT capability may be provided on a trip unit with
or without control power. If 24 volts is provided to
the RELT input, the trip unit will use the RELT
Instantaneous trip setting. However, without control
power connected to the trip unit permanently,
indication that the trip unit is in the RELT mode
may not be reliably communicated. If reliable
communication that the trip unit is in the RELT mode
is desired, it is suggested that the trip unit be per-
manently connected to 24v dc control power.
Zone Selective Interlocking (ZSI)
The EntelliGuard TU trip unit's Zone Selective
Interlocking (ZSI) capability differs from that
found in other circuit breaker trips in two
significant ways:
1. It allows independent and separate settings of
the unrestrained (in zone protection) and the
restrained (back up protection) bands.
2. It provides simultaneous and independent ZSI
of both the Short Time and Instantaneous
protection. This allows each circuit breaker to
zone interlock with upper tier circuit breakers
between ST band to ST band, Instantaneous to
Instantaneous, or Instantaneous to Short Time.
The EntelliGuard TU Trip Unit may offer the fastest
Zone Selective Interlocking (ZSI) system in the
industry. It is able to interlock Ground Fault, Short
Time and Instantaneous clearing times, and to
allow for separately set bands, including the
sloped I 2 t bands for both Short Time and Ground
Fault. The trip unit allows independent setting of
time bands so any circuit breaker will have a base,
unrestrained time band and a restrained time