f)Excessive pitting

A) Excessive pitting and welding of contacts chattering is caused by following reason

1) Reasons: Coil not picking due to low voltage

Remedy: Ensure correct voltage conditions In case of persistent low voltage change coil to lower voltage or change control transformer tapping

2) Reason: Broken Short circuit ring (Shading ring)

Remedy: The mechanical life of contactor is over. Replace the contactor

3)Chattering in switching device
Remedy: Check & correct the condition in the control circuit


4)Reason: Small cross section/long length
Remedy: Select sizes as per guideline in sect on of control cable control wiring

5)Reason: Improper termination of control cable
Remedy: Use proper lugs for termination

6)Inadequate capacity of control transformer
Remedy: Use correct control transformer



7)Reason: Capacitor switching
Remedy: Use correct contactor & follow guidelines

8)Reason: Short circuit during star delta changeover
Remedy: – Use 7PU 60 20 timer

9)Reason: Reversing application (cranes)
Remedy: Use interlocked contactors with electrical interlocking


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