What is Unintended Car Movement Protection (UCMP)?
What is Unintended Car Movement Protection (UCMP)?
What is Unintended Car Movement Protection (UCMP)?
UCMP Educational Series – Part 2 of 6
In the last post, we defined Unintended Car Movement (UCM) and looked at what causes it. Now, we turn to the code’s solution: Unintended Car Movement Protection (UCMP).
UCMP is designed to detect UCM and stop the car before it creates a safety hazard for passengers. Both ASME A17.1-2022 and ASME A17.3-2023 require that new and existing elevators include this protection.
From ASME A17.3 Section 3.10.14 and A17.1 Section 2.19.2:
“Protection shall be provided with a means to detect unintended car movement […] and stop the car movement […under certain conditions]”
There are two parts to this requirement:
- Detecting UCM
From the code:
“Detect unintended car movement 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.”
In other words, if the car begins to move up or down from a landing when it is not supposed to, and that movement exceeds the normal range of expected motion, the system must detect it quickly enough for the emergency brake to stop the car within the defined limits, while still allowing for minor, expected motion such as ropes’ stretch or relaxation during car loading and unloading.
- Stopping UCM
From the code:
“Upon detection of unintended car movement, stop and hold the car […] by applying an emergency brake […]. The stopped position of the car shall be limited in both directions, to a maximum of 1220 mm (48 in.) as measured from the landing sill to the car sill.”
Once UCM is detected, the car should not move more than 48 inches up or down.
Reset requirement:
Once activated, “the car shall not start or run unless the emergency brake provided for the unintended movement protection is reset.”
UCMP watches the elevator constantly and acts the moment something goes wrong, completely indent of the other control logic. Think of it as a safety layer built on top of the standard elevator controls. Even if a motor, brake, or other critical component fails, UCMP reduces the risk of injury by preventing the car from drifting more than 48 inches.
In the next post, we will discuss why UCMP was added to the code and how it helps prevent real-world accidents.
