Look up magnetic/relay starters. They are used on lots of machine tools with switches that provide only momentary contacts. Basically, you have a relay with the coil in series with a set of N.O. contacts. Thus, once the coil is energized, it stays energized. But once the circuit is broken, you must hit the "on" switch to start it again. If there is power interruption, as when you turn that monster off, the relay opens so the circuit will not start until you tell it to start. John