An interlock mechanism for preventing or enabling the operation of a handle operator or a contactor in certain circumstances comprises a system of mechanical linkages which interact to determine whether a lock-out mode or an enabling mode exists with respect to the electric motor being controlled. In the handle assembly, the lock-out bar has a circular aperture that receives a push rod in the enable mode and blocks the push rod in the lock-out mode. The push rod is connected to a blocking bracket which must be depressed by a human operator prior to cycling the handle operator. If the blocking bracket cannot be fully depressed by the human operator because the push rod is blocked by the lock-out bar, then the human operator can not cycle the handle operator between its OFF and ON positions, thus a first half of the interlock is achieved. Conversely, the interlock is also designed to prevent the contactor from supplying power to the electric motor if the handle operator is being cycled. If the switch has been closed (handle operator is in the ON position) and power has been supplied to the contactor but not yet to the electric motor, and the blocking bracket has been activated successfully such that the push rod has engaged the lock-out bar, then the contactor pawl assembly is unable to move and thus the contactor cannot be command to supply power to the electric motor. Thus a two way mechanical interlock is achieved.