Abstract: A protection control circuit for a variable speed hoisting device driven by an induction motor includes, in addition to the inverter unit 1 for supplying power to the induction motor 2 and relays, a rotary encoder 16 and an abnormality detector 15. When the rotary encoder 16 does not generate output in spite of the fact that an operation instruction is input, the abnormality detector 15 opens the normally closed contact 15b2 to stop the inverter unit 1 and turns on the invertor abnormality display lamp 15d1 and rotation detector abnormality display lamp 15d2.

Abstract: A variable speed electric hoist includes an invertor unit for frequency-controlling the speed of rotation of a lifting motor, a brake on/off section for turning off a brake according to a command produced from the invertor unit while the invertor unit is supplying a three-phase AC current to the lifting motor. The electric hoist also includes an emergency brake turn-on section for detecting a condition that a command produced from the invertor unit is not stopped after a lifting/lowering command is stopped to thereby turn on the brake upon detection of the condition.