Lift chooses to take a holiday on Sunday!

Most of us may have heard the interesting story about a car breaking down every time its owner bought vanilla ice cream. (If not, you can read it here: Vanilla Ice Cream and Car Breakdown Story).

A similar incident happened to me early in my career.

Several years ago, when I was a rookie engineer at a lift company, we faced a curious issue. The owner of a commercial complex where we had installed a lift complained that the over-speed governor always trips on Sundays or public holidays.

For those unfamiliar, an over-speed governor is a critical safety device. It activates if the lift exceeds its normal speed due to abnormal conditions—such as the snapping of steel cables supporting the lift car—and brings it to a safe stop. However, resetting the governor is a cumbersome task, so false triggers can be a major source of irritation.

The building was located near my home, so my manager asked me to monitor the lift on the next Sunday. I was skeptical—how could a machine "choose" Sundays to act up? Nevertheless I agreed (not that I had much say in the matter).

Sure enough, on Sunday, the lift got stuck due to the over-speed governor tripping. After resetting it, I checked the incoming phase-to-phase voltage. To my surprise, the voltage was unusually high—about 460 volts.

Then it hit me! On Sundays, the building's electrical load was minimal, causing the transformer’s output voltage to rise. This increased voltage reduced the slip of the lift’s induction motor, making it run slightly faster than its rated speed. Because the over-speed governor was calibrated with very tight tolerances, even this minor increase triggered the safety device.

We reported the issue to the local electricity board, who adjusted the transformer settings to regulate the voltage. Once this was done, the problem vanished—the over-speed governor stopped tripping unnecessarily.

The moral of the story is that unexpected problems often have simple logical explanations. It also emphasizes the importance of understanding how interconnected systems behave, as small changes in one part of a system can have significant effects elsewhere.

Another important learning is that a customer's complaint often points to a real problem—listen carefully, investigate thoroughly, and address the root cause.