Disconnector switches interlock takes 3 basic forms in substations:
- Mechanical cam-action type (figure left): used to interlock a disconnect switch and its integral grounding blades to prevent the disconnect switch from being closed when the grounding blades are closed and to prevent the grounding blades from being closed when the disconnect switch is closed.
- Key type (middle figure): a mechanical plunger extension and retraction only or electromechanical equipment consisting of a mechanical plunger and either electrical auxiliary switch contacts or an electrical solenoid. It is used in a variety of applications including, but not limited to, interlocking a disconnect switch and its integral grounding blades, interlocking the grounding blades on one disconnect switch with a physically separate disconnect switch in the same circuit, or interlocking a disconnect switch with a circuit breaker (to ensure that the circuit breaker is open before the disconnect switch is allowed to open).
- Solenoid type (right figure): most commonly used to ensure that the circuit breaker is open before the disconnect switch is allowed to open.