Glossary
Interlock
A combined mechanical latch and electrical contact on each landing door that prevents the door from opening unless the car is present, and confirms to the controller that the door is fully closed and locked.
The door interlock is one of the most important safety devices on an elevator. Every landing door (hoistway door) has an interlock assembly consisting of a mechanical latch that physically locks the door panels shut and an electrical contact that signals the elevator controller when the latch is engaged. The elevator cannot move unless every interlock in the system is proven closed — this is an absolute safety requirement enforced by code.
When the car arrives at a floor, the door coupler on the car engages the interlock mechanism and unlocks the landing door. The door operator then opens both the car doors and the landing doors simultaneously. When the doors close, the interlock re-latches and the electrical contact closes, completing the safety circuit and allowing the car to travel. Dirty, pitted, or misadjusted interlock contacts are one of the most common causes of door faults and service callbacks.