23
Instructional Leaet IB2C12063H03
Effective March 2012
Instructions for Installation, Operation and
Maintenance of Magnum SB Insulated Case
Low Voltage Power Circuit Breakers
EATON CORPORATION www.eaton.com
Figure 28. Circuit Breaker Closing Springs Being Manually Charged
Electrical Operation
For electrically operated circuit breakers, the springs are
normally charged through the use of an electrical operator
(Figure 29). The springs can, however, be charged manually as
just described in the previous paragraph (Figure 28).
Like the manually operated circuit breaker in the previous
paragraph, electrically operated circuit breakers can also be
manually closed and opened through the use of the front
mounted Manual “ON” and Manual “OFF” buttons.
An electrically operated circuit breaker from the factory is also
equipped as standard with a spring release to close the circuit
breaker electrically. An optional shunt trip and undervoltage
release are also available to trip (open) an electrically operated
circuit breaker. Refer to “Accessory Devices” on page 48 for
more details on both standard and optional devices.
Anti-Pump Feature
The Magnum SB circuit breaker has both mechanical and
electrical 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
spring release, it will not make subsequent attempts to close
until the close command is removed and reapplied. Note that
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 (Refer to page
49 for details) which will block the application of the electrical
close command until the breaker is ready to close.
Electrical Motor
Operator
Figure 29. Electrical Motor Operator to Charge Closing Spring
Arc Chambers
The Magnum SB circuit breaker utilizes arc chambers to
insulate and isolate individual poles from one another, from the
rest of the circuit breaker, and from operating personnel (Figure
17). Arc chambers are molded and integral parts of the circuit
breaker frame. Enclosed within each arc chamber is an arc
chute which mounts over each set of primary contacts.
After the main contacts part, any remaining current is driven to
the arcing contacts (Figure 30). Magnetic action draws the arc
to the arc chute. As the arcing contacts separate, the moving
arcing contacts discharge into the arc chute plates while the
integral arc runner also helps to draw the arc into the arc chute
(Figure 32).
Arc Chute
The Magnum SB arc chute mounts down over the arcing
contact. V-shaped arc chute plates attract the arc and interrupt
it. The top arc plate, which is a part of the arc chute itself, also
helps to attract the arc away from the moving arcing contact
and up into the arc chute’s V-shaped plates (Figure 31). Arc
chute components are assembled in an insulating jacket, which
is removable from the top of the circuit breaker. Each arc chute
has a baffled top cover.
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