Which description best defines the function of an interlock or safety switch on equipment?

• A. It prevents operation when a guard or access is open.
• B. It provides audible alerts when maintenance is due.
• C. It records operating hours for maintenance.
• D. It adjusts machine speed automatically.

Answer: (D)

Safety interlocks are designed to keep moving parts guarded by ensuring the machine can’t operate when a guard or access door is open. The switch is wired into the machine’s control circuit so that opening the guard immediately interrupts power or stops the machine, and it won’t restart until the guard is closed and the proper reset or start action is taken. This creates a fail-safe condition: the machine must be in a guarded state for safe operation.

So, the key idea is that the interlock prevents operation if access is open, rather than providing alerts, logging maintenance, or automatically changing speed.