See image below for an example of 3 wire control being used to pull in a contactor to start a 3 phase motor.
Start stop circuit contactor.
Basiclly you press start button which powers the coil which then pulls in the contactor once the contactor makes the feed from the stop button holds the coil in untill the stop button is pressed which breaks the circuit.
Note that one one of the contactor acts as a switch for the start button.
Step by step procedure for the basic stop start control wiring and diagram on a magnetic contactor with nc and no push button switch and how does it works.
The most common use of 3 wire control is a start stop control.
The contactor is operated by the control circuit energizing a coil as in the example above.
A simple circuit diagram either of the two start buttons will close the contactor either of the stop buttons will open the contactor.