26
I.B. 8926-1A
CONTACT WEAR AND REPLACEMENT
Contactors are subject to both mechanical and
electrical wear during their operation. In most cases
mechanical wear is insignificant. The erosion of the
contacts is due to electrical wear. During arcing,
material from each contact is vaporized and blown
away from the useful contacting surface.
A critical examination of the appearance of the
contact surfaces and a measurement of the
remaining contact over-travel will give the user the
information required to get the maximum contact life.
OVER-TRAVEL MEASUREMENT
Contact life has ended when the over-travel of the
contacts has been reduced to .020 inch.
Over-travel of the contact assembly is that part of
the stroke which the moving contacts would travel
after touching the fixed contacts if they were not
blocked from movement by the fixed contacts.
A method of measuring over-travel is as follows:
A. Place a .020 inch feeler gauge between the
armature and magnet, with the armature held
tightly against the magnet.
B. Check continually in each phase, i.e.,
determine if circuit from terminal-to-terminal for
each pole is open under these conditions.
C. If there is continuity through all phases, the
remaining over-travel is sufficient. If there is not
continuity through all phases, replace all
stationary and moving contacts plus moving
contact over-travel springs. After replacing
parts, manually operate contactor to be sure
binding does not occur.
DEFECT
CAUSE
REMEDY
Short contact
life
Low contact
force
Adjust overtravel, replace
contacts, and replace contact
springs as required to correct
contact force.
Contact bounce
on opening or
closing
Correct improper voltage
applied to coil. Correct any
mechanical defects or
misalignment.
Abrasive dust
on contacts
Do not use emery cloth to
dress contacts.
Load current is
too high
Reduce load. Use larger
contactor.
Jogging cycle
is too severe
Reduce jogging cycle. Check
factory for more durable
contact material. Use larger
contactor.
CONTACTOR TROUBLESHOOTING CHART
DEFECT
CAUSE
REMEDY
Overheating
Load current
too high
Reduce load. Use larger
contactor.
Loose
connections
Clean discolored or dirty
connections and retighten.
Replace poorly crimped lugs.
Over-travel
and/or contact
force too low
Adjust over-travel, replace
contacts, and replace contact
springs as required to correct
defect.
Ambient
temperature
is too high
Reduce load. Provide better
ventilation. Relocate starter.
Use larger contactor.
Line and/or
load cables
are too small
Install terminal block and
run larger conductors
between contactor and
terminal block.
CONTACTOR TROUBLESHOOTING CHART
Welding of
contacts
Overtravel
and/or contact
force is too low
Adjust overtravel, replace
contacts, and replace contact
springs as required to correct
contact force.
Magnet
armature stalls
or hesitates at
contact touch
point
Correct low voltage at coil
terminals as coil draws inrush
current.
Contactor
drops open to
contact-touch
position
because of
voltage dip
Maintain voltage at coil
terminals. Install low voltage
protective device, sometimes
called "Brownout Protector".
Excessive
contact bounce
on closing
Correct coil overvoltage
condition.
MAINTENANCE OF MOTOR CONTROLLERS
AFTER A FAULT
=
In a motor branch circuit which has been properly
installed, coordinated and in service prior to the
fault, opening of the branch-circuit short-circuit
protective device (fuse, circuit breaker, motor short-
circuit protector, etc.) indicates a fault condition in
excess of operating overload. This fault condition
must be corrected and the necessary repair or
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