The limit switch is operated by contact with the crane hook block. When activated, the limit switch interrupts power to the lift motor. This prevents the hook block from colliding with the cable drum, which could cause a dropped load or other unsafe situation.
Limit switches were introduced to the industrial market in the 1920s by manufacturers such as Square D and Cutler -Hammer. Many of these designs are still in use today.
Limit switches may be remanufactured using specialized parts that are currently available.