Effective 8/13/99
Page 4
I.L. 70C1037H02
The Digitrip 220, 520, and 520M trip units may be applied
on both 50 and 60 Hz systems.
Digitrip DT20 family of trip units are microprocessor-
based ac protection 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 protec-
tion. 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
adjustments 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 Digitrip DT20 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 through 3.9.
NOTE: The Digitrip 220 (LI model), 520 (LSI model), and
520M (MLSI model) can be used on 3-pole or 4-pole
circuit breakers for the protection of the neutral circuit.
Only these three models can provide neutral protection,
although models MLSIA,MLSIG, and MWLSIG can
provide neutral metering (see Figures 3.7, 3.8, and 3.9).
Refer to the National Electric Code (NEC) for the appro-
priate application for 4-pole breakers.
1.2 Mode of Trip and Status Information
On all DT20 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 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.
