Magnetic Contactor

When you say the contactor is burned, I assume you mean the contacts. Are they pitted or welded? My experience is that contacts are often crappy; the days of silver on silver-carbide are about gone.

You might look at adding some arc suppression. Is there any possibility the pump is starting under load, or that the contactor is bouncing during operation (maybe the 120 V is dropping low)?

thank a lot for you reply...

In simpler terms:

45A is not a very common industrial size contactor rating, you may have something special, such as a "definite purpose" contactor. Contactors are rated for more than just amps. You must know the duty as well. A contactor rated for 45A as a resistive load will not necessarily handle a 9kW inductive load such as a motor, and if the motor is turning on and off rapidly, it may be severely under sized. You need to investigate your application better.

As mentioned by others, a common problem with early contactor failure is rapid cycling. This can be caused by a poor control circuit connection, or a failing device such as a float/pressure/flow switch in another part of the circuit, or a bad control system design where there is no "hysteresis", a difference between the On and Off points, sufficient to avoid this problem.

thanks a lot for your comment ,yes, your right because our level sensor is failing- the sensitivity isn't in good setting.

hi,

your explanation is unclear, what was burned & what you've changed ...if the coil burnt then you have to check the voltage that could be unstable or different freq with the magnetic coil.

you also stated that the pump motor is 9000 Watts in which if it is 3 ph equal to 43 Amp or 75 Amp for 120 V/1Ph , meaning that your contactor rating was under capacity so my suggestion is try sizing the contactor for at least 1.5 times of load capacity & choose the heavy duty AC 3 type, if the pump is 1 phase, it's best wiring contactor outputs serially. thanks