Electrical Operation; Anti-Pump Feature; Section 4: Circuit Breaker Features And Accessories; Introduction - Eaton NRX Instruction Manual

Section 4: Circuit breaker features and accessories

Figure 27. Step 3.
Optional electrically operated accessories are available to
automatically close/trip a manually operated breaker.

Electrical operation

The springs on an electrically operated circuit breaker are
normally charged automatically through the use of an electri-
cal operator. The springs can, however, be charged manual-
ly as just described in the last section. Electrically operated
circuit breakers can also be manually closed and opened
through the use of the front mounted ON and OFF buttons.
An electrically operated circuit breaker can be equipped with
an optional spring release (closing coil) to close the circuit
breaker remotely. The breaker can also be equipped with a
shunt trip (opening coil) to open the breaker remotely.
IMPORTANT
!
Different degrees of access to pushbuttons on the front
of the circuit breaker can be achieved through the use of
optional accessory devices.

Anti-pump Feature

Series NRX circuit breakers have both mechanical and elec-
trical anti-pump features. If the circuit breaker is closed on
a fault condition and trips open while the CLOSE signal is
maintained (using either the mechanical pushbutton or the
electrical close coil), it will not make a subsequent attempt
to close until the close command is removed and reapplied.
N ote: If the close signal is applied prematurely (before the
breaker is completely charged and latched), the close
command will be ignored until it is removed and
reapplied.
For electrical closing, a Latch Check Switch (LCS) option is
available that will block the application of the electrical close
command until the breaker is ready.
16
Series NRX with PXR - type RF low voltage power (air) circuit breakers instruction manual MN013002ENH03 September 2016 www.eaton.com
Section 4: Circuit breaker features and accessories

Introduction

The features and accessories of the drawout and fixed con-
figurations are covered briefly in this section. Details and
installation instructions on trip units and individual accesso-
ries 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 three-part tripping system:
Microprocessor-based trip unit connected to a frame
●
rating module;
Rogowski coil type current sensors; and
●
Trip actuator.
●
All three parts of the tripping unit are discussed here in
general. For detailed information pertaining to the different
available trip unit models and other breaker or accessory
information, refer to Eaton's website www.eaton.com/
seriesnrx.
See important frame rating module information on next
page regarding the tripping system.

Microprocessor-based trip unit

Series NRX circuit breakers utilize the PXR family of elec-
tronic trip units whose main features are summarized in
Table 2. Digitrip trip units are still available for purchase on
IEC breakers.
The electronic trip units are self-powered devices (Figure
24). The protection settings can be set from the front panel.
When the circuit breaker is closed, no external power is
required to operate their protective systems. Current sig-
nal levels and the control power are derived from the cur-
rent 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 performed through the trip unit's USB receptacle
(Figure 5).