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6.
Fig.
Moving Contact Assembly (4000A)
Detailed Inspection
Make sure that all bolts, nuts, terminal connections, etc. are
fastened securely. Check for evidence of wear or improper
adjustment and operation of the various parts.
The machined surfaces of the armature and holding magnet
should be inspected carefully to make sure that they are free
of dirt or magnetic particles. The surfaces should be cleaned
occasionally with a clean cotton cloth dipped in kerosene. Cot
ton waste should be avoided since loose fibers may be left on
the magnet surfaces.
After a long period of service or exposure to moist or corrosive
air, the magnet surfaces may be rusted or corroded to some
extent. A small amount of rust will not interfere with breaker
operation. If rust or distortion occurs to the extent of interfering
with proper holding, the surfaces may be trued as follows:
1. Holding magnet- use a fine grit, flat stone and carefully
rub it over the surface of the magnet until flatness is restored.
2. Armature surface- remove the armature from the breaker.
Lay a sheet of polishing cloth or very fine emery paper with
the grit side up on a surface plate. Lay the ar � ature ? n the
polishing cloth and move it about carefully w1th a c1rcular
motion until all high spots are removed.
1.8. 201
7.
Fig.
ARC Chute
CAUTION
The arc chamber contains ceramic material. Handle
carefully. Do not drop, tip over or bump.
Insulating parts of the arc chamber must withstand more than
the full line potential when the breaker is interrupting. Suc
cessful breaker operation depends largely on the care given
to the arc chambers. Periodically, they should be removed and
inspected for worn or broken ceramic parts and for excessive
metallic spray deposits.
Since fault currents vary in severity , the life of an arc chamber
cannot be predicted accurately. Renewals should be deter
mined by inspection. If the ceramic plates are eroded to sharp
edges, or if the slot s in the plates have increased more than
%inch in width in the widest portion, the arc chamber should
be replaced. If any of the ceramic plates are badly cracked, the
arc chamber should be replaced.
When installing the arc chamber on the breaker, make certain
that the rear arc-runner connection engages the clips on the
blow-out magnet assembly, Fig. 7.
5
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