Electrical Principles and Operation of Electric Hoists

Mar 2, 2026

The electrical schematic diagram of an electric hoist is shown in Figure 2-2. In this system, M1 is the hoisting motor, responsible for lifting and lowering the hook, while M2 is the traverse motor, responsible for moving the hook forward and backward.

Hoisting Motor (M1) Control

When the “Up” button switch SB1 is pressed, the electromagnetic coil of contactor KM1 is energized, closing its main contacts and causing motor M1 to rotate forward to lift the hook. Releasing SB1 de-energizes the KM1 coil, resetting its contacts and stopping motor M1.

When the “Down” button switch SB2 is pressed, the electromagnetic coil of contactor KM2 is energized, closing its main contacts and causing motor M1 to rotate in reverse to lower the hook. Releasing SB2 de-energizes the KM2 coil, resetting its contacts and stopping motor M1.

Traverse Motor (M2) Control

When the “Forward” button switch SB3 is pressed, the electromagnetic coil of contactor KM3 is energized, closing its main contacts and causing motor M2 to rotate forward. Releasing SB3 de-energizes the KM3 coil, resetting its contacts and stopping motor M2.

When the “Reverse” button switch SB4 is pressed, the electromagnetic coil of contactor KM4 is energized, closing its main contacts and causing motor M2 to rotate in reverse. Releasing SB4 de-energizes the KM4 coil, resetting its contacts and stopping motor M2.