Unintended movement, and the protection that assumes it will happen

Most elevator failures are inconveniences: a car stops between landings, a door refuses to close, a call is not answered. One failure is not an inconvenience. It is the car leaving the landing while the doors are open and somebody is standing in the doorway.

Two failures, two protections

Unintended car movement is exactly that: the car moves away from the landing with the doors not closed and not locked, for a reason that has nothing to do with a call. A brake that does not hold, a rope that slips, a control that releases when it should not. The protection detects the movement and stops the car within a defined distance, independently of whatever failed.

Ascending overspeed is the other one, and it is less intuitive. A safety gear grips the guide rails when the car descends too fast, because that is the direction gravity pulls. But a counterweighted system can also run away upward with an empty car, and a descending safety gear does nothing about that. Ascending overspeed protection covers the direction the classic device does not.

What it costs the drawing

Both devices live in the hoistway, and both need somewhere to be. Depending on how the protection is resolved, it either integrates into the machine brake or arrives as a separate gripping device on the rails, and either way it asks for clearance in the head, in the pit, or along the rail line. This is why it is worth knowing about it while the shaft is still a rectangle on a drawing, and not once it is poured.

What else rides along

• Overload protection stops the car from starting when the load exceeds what it was rated for.
• The light curtain keeps the doors from closing on a person or an object in the doorway.
• An automatic rescue device brings the car to the nearest landing and opens the doors on a power failure, instead of holding passengers until service arrives.
• An earthquake sensor parks the car at the nearest landing before the tremor reaches full amplitude.

Unintended-movement and ascending-overspeed protection ship as standard on every Weston configuration. The certification set is in the Download Center.