The electromechanical safety switch fitted to every landing door and car door that is wired in series in the elevator safety circuit and prevents the elevator from moving unless all doors are fully closed and mechanically locked.
Full Definition
The door contact (also called door interlock, door safety switch, or door lock) is one of the most critical safety devices in an elevator installation. Every landing door is fitted with a mechanical locking device (latch bolt or hook bolt) and an electrical contact that can only confirm a closed and locked state when the landing door is fully shut and mechanically engaged. EN 81-20 requires: (1) Every landing door contact wired in series in the safety circuit — if any single door contact opens (door ajar), the safety circuit breaks and the elevator stops or cannot start; (2) The electrical contact must not close until the mechanical lock is fully engaged (called an interlock sequence); (3) The car door(s) have separate contacts; (4) The contact must be rated for the electrical conditions and be of a positive-break design (spring-return to open). In a typical 10-floor building there are 20 or more door contact points in the safety circuit. A door contact failure is one of the most common causes of elevator stoppages. Modern digital safety circuits (e.g. PESSRAL — Programmable Electronic Systems in Safety-Related Applications for Lifts, per EN 81-20/50) may use safety-rated microprocessor monitoring of door states instead of traditional series-wired contacts, but must meet SIL (Safety Integrity Level) requirements.
