circuit breakers, refer to the specific trip unit instruction book
for details.
3-7.1 Electronic Trip Unit
Types DSII and DSLII circuit breakers, whether manually
or electrically operated, are supplied with a state-of-the-art
electronic, microprocessor-based trip units. True RMS sens-
ing is provided for proper correlation with thermal character-
istics of conductors and equipment.
In addition to circuit protection, electronic trip units provide
information and integral testing functions. Optional remote
communications and energy monitoring functions are also
available.
The electronic trip units are completely self-contained and,
when the circuit breaker is closed, no external power is
required to operate their protection systems. They operate
from current signal levels and the control power is derived
from current sensors integrally mounted in the circuit
breaker.
When the circuit breaker is shipped from the factory, the
trip unit’s protective functions are normally set at nominal
values. For specific overload tripping characteristics to coor-
dinate with the load or system, refer to the specific trip unit
instruction book.
3-7.2 Sensors
Three current sensors are installed at the rear of the circuit
breaker on the lower studs, directly behind the main discon-
necting contacts (Figures 3-1 and 3-2). The sensors produce
an output current proportional to the load current. Under
preselected conditions of current magnitude and time, the
sensors furnish the electronic trip unit with a signal and the
energy required to trip the circuit breaker.
Since the continuous current rating for any frame size
breaker is associated with both the sensors and the trip unit
itself, a complete tabulation of available current sensors is
presented in the specific trip unit instruction book, not this
instruction book for the circuit breaker.
3-7.3 Trip Actuator
The electronic trip unit provides a pulse to the trip actuator,
which produces a mechanical force to trip the circuit breaker
(Figure 3-11). The actuator is comprised of a permanent
DTA Plunger
Trip Shaft
Lever
Untripped
Tripped
Trip
Shaft
DTA Reset
Lever
Breaker
Open
Pole Shaft
Lever
Breaker
Closed
Actuator Reset
DTA
Actuator
Frame
Figure 3-11 Type DSII Trip Actuator
Effective July 2010
Instructional Book
IB694C694-03
22
eaton corporation
www.eaton.com
