Effective 2/2/2001
Page 4
I.L. 70C1037H03
All trip unit models are microprocessor-based ac protec-
tion devices that provide true RMS current sensing for the
proper coordination with the thermal characteristics of
conductors and equipment. The primary function of the
Digitrip Trip Unit is circuit protection. The Digitrip analyzes
the secondary current signals from the circuit breaker
current sensors and, when preset current levels and time
delay settings are exceeded, will send an initiating trip
signal to the Trip Actuator of the circuit breaker.
In addition to the basic protection function, the Digitrip 520
family of trip units provides mode of trip information such
as:
•
Long Time trip (overload)
•
Short Time trip
•
Instantaneous trip
•
Ground (Earth) Fault trip (if supplied).
The current sensors provide operating power to the trip
unit. As current begins to flow through the breaker, the
sensors generate a secondary current which powers the
trip unit.
The Digitrip 520 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 adjust-
ments is optional. The short delay and ground fault pick-up
adjustments can be set for either FLAT or I
2
t response. A
pictorial representation 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.
1.1 Protection
Each trip unit is completely self-contained and requires no
external control power to operate its protection systems. 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
and Figures 3.2.1 through 3.4.4.
NOTE
: The Digitrip 220 (LI model), 520 (LSI model), 520M
(MLSI model) and 520MC (CLSI model) can be used on 3-
pole or 4-pole circuit breakers for the protection of the
neutral circuit. Only these four models can provide neutral
protection, although models MLSIA,MLSIG, MWLSIG,
CLSIA, CLSIG and CWLSIG and can provide neutral
metering (see Figures 3.7, 3.8, and 3.9). Refer to the
National Electric Code (NEC) for the appropriate applica-
tion for 4-pole breakers.
1.2 Mode of Trip and Status Information
On all models, 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
also blink at a faster rate if the Digitrip is in a pick-up, or
overload, mode.
Red LEDs on the face of the 520 family of trip units (for
Long Delay, Short Delay, and Instantaneous) 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/Battery Test button is pushed.
The battery is satisfactory if its LED lights green when the
Battery Check button is pushed
(See Section 6)
.
NOTE:
The Digitrip 520 family provides all protection
functions regardless of the status of the battery. The
battery is only needed to maintain the automatic trip
indication.
1.3 Installation and Removal
1.3.1 Installation of the Trip Unit
Align the Digitrip unit with the guide pins and spring clip of
the Magnum Circuit Breaker. Press the unit into the
breaker until the pins on the trip unit seat firmly into the
connector housing and the unit clicks into place
(See
Figure 1.2).
1.3.2 Rating Plug Installation
WARNING
DO NOT ENERGIZE THE MAGNUM BREAKER WITH
THE DIGITRIP REMOVED OR DISCONNECTED FROM
ITS CONNECTOR. DAMAGE TO INTERNAL CURRENT
TRANSFORMERS MAY OCCUR DUE TO AN OPEN
CIRCUIT CONDITION.
CAUTION
IF A RATING PLUG IS NOT INSTALLED IN THE TRIP
UNIT, THE UNIT WILL TRIP WHEN IT IS ENERGIZED.
Insert the rating plug into the cavity on the right-hand side
of the trip unit. Align the three pins on the plug with the
sockets in the cavity. The plug should fit with a slight
insertion force.
