I have a chattering problem on the 3 phase contactor of a large water pump control circuit.
The cct is opperated by an 'manual off auto' switch. When energised in the 'manual' position the contactor holds firm. However when opperated in the 'auto' position I get 3 or 4 chatters and then a firm hold. Obviously over time this causes the contacts to fail. The contactor has been replaced twice already for the same problem.
The cct has two 3 phase contactors, one with an overload, an off timer, an on timer, an on off auto switch, and a relay which operates the two timers. Its probably a bit complicated to explain on here.
Just wondering does anyone know why it opperates perfectly in manual mode but not in auto??
Much appreciated!

Beau

I would be checking, or replacing the timers. I assume these are TDR relays.

Is it possible to measure the coil voltage in auto mode?

The chattering can be caused by low voltage, which could be a result of a bad contact in a TDR, or any loose wire termination.

Or a TDR has a weak coil, that pulls in slowly, causing the TDR contacts to make/break repeatedly, causing the main contactor coil to chatter.

If you can get your hands on a recording instrument, to measure and record voltage at various locations in the auto circuit, starting at the Main Contactor coil would be helpful to pinpoint the problem.