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24
Operation and maintenance of
IZM low voltage air circuit breakers
MOELLER
www.moeller.net/de/support
10/09 AWB1230-1605
Effective October 2009
Figure 28. Pictorial Diagram of Typical Current Sensing, Processing, and Tripping System
A
B
C
N
G
A
B
C
N
01
02
03
Toroidal
Current
Sensor
Rating Plug
Trip Unit
Trip Actuator
Typical IZM Circuit
Breaker
Sensors
otee:
N
Alternate ground locations may be
required to meet installation requirements.
circuitry and the circuit breaker’s mechanical tripping action can be
verified through the trip unit’s test receptacle (
). This is
accomplished using a Digitrip Test Kit that provides a secondary
injection test that simulates the current sensors. A small hand-
held IZM functional Test Kit can also be used to check circuitry and
mechanical tripping functions (
When the circuit breaker is shipped from the factory, the trip
unit’s protective functions are normally set at minimum values.
For specific overload tripping characteristics and time/current
curves to coordinate with a load or system, refer to the trip unit
instruction book.
Microprocessor-based trip unit
IZM circuit breakers use any one of a family of Digitrip
E
RMS trip
units whose main features are summarized in
.
Table 4. IZM Digitrip Trip Units
Functions
520L
i
520
i
520M
i
a
520MC
i
a
1150
i
a
LSIG protection
No
Yes
Yes
Yes
Yes
Disable (I)
No
Yes
Yes
Yes
Yes
GF protection
No
Yes
Yes
Yes
Yes
GF alarm
No
No
Yes
Yes
Yes
Display
No
No
Yes
b
Yes
b
Yes
c
Programmable
No
No
No
No
Yes
Metering
No
No
Yes
Yes
Yes
Power and energy values
No
No
No
No
Yes
Power quality
No
No
No
No
Yes
Communication
No
No
No
Yes
Yes
a
Available control voltages are 24–48 Vdc, and 120 and 240 Vac.
b
One-line, (four characters per line) LCD display.
c
Three-line, (eight characters per line) LED display.
Phase, neutral, ground, and high load current only.
All the electronic trip units are self-powered with regard to their
protective functions. Current signal levels and the tripping energy
are derived from the current sensors integrally mounted in the circuit
breaker. Control power is required to operate certain optional display
and metering functions.
A functional local test of a major portion of the trip unit’s electronic