Uncontrolled acceleration causes elevator damage
July 18, 2017
It was reported to Technical Safety BC that during maintenance troubleshooting, an elevator accelerated in an uncontrolled manner into the elevator shaft overhead.
Regulated industry sector
Elevating - Elevator
Site, system and components
Elevator controllers are designed to control the normal operation of the elevator. Elevator controllers can control speed, braking, acceleration and other functions. Elevator controllers have circuit boards that control certain functions of the elevator. Each circuit board has a designated slot in the controller. The elevator is designed to operate only with all of the circuit boards in their designated slots.
Elevator “motion control devices” are devices meant to shut down and arrest any uncontrolled motion of an elevator. Elevator “motion control devices” engage the elevator braking system. Elevator brakes are designed to hold 125% of the designed rated load. Elevator brakes are designed to stop an elevator that has gone into a uncontrolled motion state ( run-away/over speed).
Service and maintenance of elevator brakes are performed with the elevator cab at the top of the elevator shaft and the elevator counterweight on the buffers ( springs/hydraulic pistons) at the bottom of the elevator shaft (ground). The elevator in this position will not move with the brakes released as the elevator counterweight is heavier than the elevator cab.
Possible failure scenario 1. The maintenance personnel removed the controller circuit boards to perform a visual inspection. The maintenance personnel replaced the circuit boards into the incorrect slots ( positions) in the controller. The elevator was energized and a command to run was made. The circuit board in the incorrect position caused the elevator to run at high speed into the elevator shaft overhead causing the reported mechanical and structural damage.
Possible failure scenario 2. Adjustments made to the elevator brake while the elevator car was at the bottom portion of the elevator shaft allowed the elevator to move in an uncontrolled manner up the elevator shaft. The counterweight being heavier than the elevator car allowed the elevator develop significant velocity. The motion control devices may have actuated, but a reduction or lack of braking force allowed the elevator car to impact the upper structural members (overhead) of the elevator shaft causing the reported mechanical and structural damage.
Facts and evidence
Maintenance Personnel Statements:
The maintenance assistant stated that: They had removed the controller circuit boards (A3 speed supervision and A4 speed regulator) for cleaning.
On-Site Investigation Observations:
Original Equipment Manufacturer - Field Engineer- Test results and remarks:
Causes and contributing factors
Based on test results performed by the field engineer it is highly unlikely that the inadvertent misplacement of the controller circuit boards (A3 and A4) into the wrong controller slots caused the uncontrolled movement of the elevator.
It is plausible that the elevator brake system was inoperable or not providing designed braking power allowing the uncontrolled movement of the elevator.
The cause of this incident is unknown.