What is Elevator Unintended Car Movement (UCM)?
What is Elevator Unintended Car Movement (UCM)?
What is Elevator Unintended Car Movement (UCM)?
UCMP Educational Series – Part 1 of 6
This is the first installment in a 6-part series on Unintended Car Movement Protection (UCMP). In this series, we will address some of the most common questions we receive about UCMP.
Unlike other industry nicknames, the phrase Unintended Car Movement (UCM) comes directly from the code. Both ASME A17.1 (new elevators) in sections 1.3 and 2.19.2.2 and ASME A17.3 (existing elevators) in sections 1.4 and 3.13.3.2 define the Unintended Car Movement protected against by UCMP in very similar terms. From A17.1:
“any movement of an elevator car that is not intended car movement, resulting from a component or system failure […] in either direction away from the landing with the hoistway door not in the locked position and the car door or gate not in the closed position.”
So what does that mean in real life?
In most cases, and in many of the videos showing this behavior online, it looks like a car drifting up or down after it has stopped at a landing. That drift can create several serious hazards:
- A tripping hazard at the landing
- The risk of falling into the hoistway
- The chance a passenger becomes trapped between the car and the floor
The code goes further by spelling out what kinds of failures meet the definition of UCM. From ASME A17.3 Section 3.13.2:
Car movement as a result of failure in any of the following:
(a) electric driving-machine motor, brake, coupling, shaft, or gearing
(b) control system
(c) any other component upon which intended car movement depends, except suspension means and drive sheave of the traction machine
In other words, if the car moves because the motor, brake, control system, or another one of these critical components fails, it is UCM.
Because of the safety impact of these failures, both A17.1 and A17.3 also spell out the solution.
In the next post, we will move from the definition of UCM to the code’s solution: Unintended Car Movement Protection (UCMP).
