Can I place a switch or contactor between the frequency inverter output and the motor?
As a general rule there should be no interruption between the drive output and the motor cable. The motor should be isolated by switching off power to the frequency inverter and then waiting for the drive bus to discharge.
A manually operated switch or contactor should never be placed between the drive and the motor as operation of the switch whilst the drive is running could result in damage to the system.
An output contactor could be used for motor disconnection provided that measures are taken to lock-in the contactor until the drive output has been disabled.