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Effective 10/2004
Page 7
I.L. 70C1036H05
If you have any questions or need further information or
instructions, please contact your local representative or
the Cutler Hammer Customer Support Center.
1.0 GENERAL DESCRIPTION OF DIGITRIP TRIP UNITS
The Digitrip Trip Units are circuit breaker subsystems that
provide the protective functions of a circuit breaker. The trip
unit is in a removable sealed housing, installed in the
circuit breaker, and can be replaced in the field by the end
user.
This instruction book specifically covers the application of
Digitrip Trip Units, as illustrated in Figure 1.1, installed in
Magnum and Magnum DS Breakers. Throughout this
Instructional Leaflet, the use of the term “Magnum Break-
ers” refers to both the Magnum and Magnum DS low-
voltage, AC power circuit breakers.
The Magnum Digitrip line of trip units consists of the 1150
which conforms to UL standards, and model 1150
i
con-
forming to IEC standards. Throughout this Instructional
Leaflet, the use of the term Digitrip 1150 trip units refers to
both models unless otherwise stated.
The Digitrip 1150 trip units may be applied to either 50 or
60 Hz systems.
Digitrip DT1150 family of trip units incorporate two micro-
processors in their design. One processor is devoted
totally to the task of current protection functions. This
processor provides true RMS current sensing for the proper
coordination with the thermal characteristics of conductors
and equipment. The Digitrip analyzes the secondary
current signals from the circuit breaker current sensors
and, when preset current levels and time delay settings are
exceeded, sends an initiating trip signal to the Trip Actua-
tor of the circuit breaker. The current sensors provide
operating power to the trip unit. As current begins to flow
through the circuit breaker, the sensors generate a sec-
ondary current which powers the trip unit.
The second microprocessor provides the voltage protection
display, communications, metering, harmonic calcula-
tions, alarming and auxiliary relay functions. These
additional features require that auxiliary power be provided
to the circuit breaker.
1.1 Protection
Each Digitrip DT1150 Trip Unit is completely self-contained
and requires no external control power to operate its basic
over current protection functions. It operates from current
signal levels derived through current sensors mounted in
the circuit breaker. The types of protection available for
each model are shown in Table 1.1.
The Digitrip 1150 family of trip units provides five phase and
two ground (time-current) curve-shaping adjustments. To
satisfy the protection needs of any specific installation, the
exact selection of the available protection function is
adjustable. The short delay and ground fault adjustments
include either a FLAT or I
2
T response. A pictorial represen-
tation of the applicable time-current curves for the selected
protection functions is provided, for user reference, on the
face of the trip unit as shown in Figure 1.1.
NOTE
: The Digitrip 1150 (11LSI ,11PLSI style) and Digitrip
1150
i
(11IEC, 11PIEC) are the styles that can be used on
3-pole or 4-pole circuit breakers for the protection of the
neutral circuit. For a 3-pole circuit breaker an external
sensor of the same rating as the phase sensor needs
wired to the circuit breaker. Only these styles can provide
neutral protection, although all styles can provide neutral
metering and alarming (one exception is that there is no
metering for source or zero sequence Ground Fault
application). These styles also have a protection setting
called Neutral Ratio. The 100% setting is the default and
is used when phase and neutral conductors are of the
same ampacity. The 50% setting is for a half sized neutral
conductor and essentually shifts the Long Time thermal
curve to the left making it more sensitive. Refer to the
National Electric Code (NEC) for the appropriate applica-
tion for 4-pole circuit breakers.
1.2 Mode of Trip and Status Information
On all DT1150 units, a green light emitting diode (LED),
labeled Status, blinks approximately once each second to
indicate that the trip unit is operating normally. This Status
LED will blink at a faster rate if the Digitrip is in a pick-up,
or overload, mode.
Red LEDs on the face of the 1150 family of trip units flash
to indicate the cause, or trip mode, for an automatic trip
operation (for example, ground fault, overload, or short
circuit trip). A battery in the Digitrip unit maintains the trip
indication until the Reset button is pushed. The battery is
satisfactory if its LED lights green when the Battery Test
button is pushed
(See Section 6).
NOTE:
The Digitrip 1150 family provides all protection
functions regardless of the status of the battery. The
battery is only needed to maintain the automatic trip
indication on the mimic curve of the Digitrip when auxiliary
power is not available.
1.3 Installation and Removal
1.3.1 Installation of the Trip Unit
Align the Digitrip unit with the molded guide ears on the
platform and spring clips of the Magnum Circuit Breaker.