What is an interlock or safety switch on equipment?

• A. A safety device that prevents operation when a guard or access is open.
• B. A timer that stops operation after a set period.
• C. A sensor that records operating hours.
• D. An audible alarm for nearby workers.

Answer: (B)

An interlock or safety switch is a protective device that ensures the equipment cannot start or continue operating unless a guard or access door is fully closed. It works by sensing the door position and interrupting the control circuit if the guard is opened; this prevents exposed moving parts from causing injury and stops the machine in a safe state if someone tries to reach into the danger area. This is different from a timer, which merely controls how long a cycle runs and does not verify whether guards are in place before or during operation. So the purpose of an interlock is guarding access and stopping the machine when a guard is opened, not timing the operation.