21
Instructional Book
MN01301003E
Effective July 2011
Series NRX Low Voltage Power (Air)
Circuit Breakers User Manual
EATON CORPORATION
www.eaton.com
Section 4: Circuit Breaker Features and Accessories
Introduction
Series NRX low voltage circuit breakers are available in both drawout
and fixed mounting configurations (
Figure 3
and
Figure 5
). All circuit
breakers are available as three-pole or four-pole breakers with the
available connection configurations and specific ratings dictated by the
applicable standards.
All features and accessories common to both the drawout and
fixed configurations are covered briefly in this section. Details and
installation instructions on trip units and individual accessories are
covered in their respective IL’s.
Arc chambers
An arc chamber, one for each pole, includes an arc chute mounted
around a set of primary contacts. The chambers act to quench arcs and
channel gases up and out of the breaker during interruption.
Electronic tripping system
Series NRX circuit breakers use a four-part tripping system:
•
Microprocessor-based trip unit
•
Rogowski coil type current sensors
•
Trip actuator
•
Rating plug amperes
All four parts of the tripping system are discussed here in general. For
detailed information pertaining to the different available trip unit models,
refer to IL01301051E (Digitrip 520) or IL01301064E (Digitrip 1150), which
are dedicated to the trip units and are available on Eaton’s web site.
Microprocessor-based trip unit
Series NRX circuit breakers use any one of a family of Digitrip RMS
trip units whose main features are summarized in
Table 4
.
The electronic trip units are self-powered devices (
Figure 25
). The
protection settings can be set from the front. When the circuit breaker
is closed, no external power is required to operate their protective
systems. Current signal levels and the control power are derived
from the current sensors. All trip units are true RMS current sensing
devices.
A functional local test of the trip unit’s primary electronic circuitry and
the circuit breaker’s mechanical tripping action can be verified through
the trip unit’s test port receptacle (
Figure 6
).
Figure 25. Installed Digitrip 520 Trip Unit
Table 4. Series NRX Digitrip Trip Units
Functions
Digitrip 520
Digitrip 520M
Digitrip 1150
LSIG protection
Yes
Yes
Yes
Disable (I)
Yes
Yes
Yes
GF protection
Yes
Yes
Yes
GF alarm
No
Yes
Yes
Display
No
Yes
Yes
Programmable
No
No
Yes
Metering
No
Yes
Yes
Power/energy
No
No
Yes
Power quality
No
No
Yes
Communication
No
Yes
Yes
