Magnum
1812.900A
49
Figure 6-2: Bottom View of Arc Chute
1. Alternating “V” Shaped Plates
Figure 6-3: Primary Contacts with Circuit Breaker Open (Not
Used for Contact Wear Inspection)
WARNING
ARC CHUTES MUST ALWAYS BE SECURED
PROPERLY IN PLACE BEFORE A CIRCUIT BREAKER
IS INSTALLED IN A CIRCUIT BREAKER
COMPARTMENT. FAILURE TO DO THIS COULD
RESULTS IN EQUIPMENT DAMAGE, BODILY INJURY
OR EVEN DEATH.
When the inspections are complete, position each arc
chute down over its respective set of primary contacts,
and secure in place with the screw removed earlier.
Torque the arc chute screws to 4 to 5 Nm.
6.4.3
Primary contact inspection
With the arc chutes removed, visually inspect each
primary contact structure for signs of wear and/or
damage. The primary contacts with the circuit breaker
open can be viewed by looking directly down into the arc
chamber (Figure 6-1 and Figure 6-2).
A contact wear indicator is provided for each primary
contact and indicates whether or not the contact should
be replaced. Inspection of the contacts using the contact
wear indicators is conducted only with the circuit
breaker closed (Figure 6-5: ).
(Side View)
Figure 6-4: Contact Inspection Area with Circuit Breaker
Open
1. Arcing Contact (Toe)
2. Integral Arc Runner
3. Stationary Main Contact
4. Moving Main Contact
NOTICE
WHEN MAKING A CONTACT WEAR INSPECTION,
ALWAYS MAKE THE INSPECTION BY LOOKING
STRAIGHT DOWN INTO THE ARC CHAMBER FOR
THE PROPER PERSPECTIVE. VIEWING THE
CONTACT WEAR AREA FROM AN ANGLE COULD
DISTORT THE VIEW.
The contact wear indicator is the relative position of the
individual contact fingers to a narrow, side-to-side ledge
inside the arc chamber. The ledge is actually part of the
arc chamber. When the circuit breaker is closed and the
contacts are in good condition, the narrow ledge is
covered by the back end of the contacts (Figure 6-5: ). If
the back end of the contacts do not totally cover the
ledge, the contacts should be replaced.
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