Elevators keep trapping passengers over and over again. Maintenance crews get called out right away, and technicians inspect door locks, safety circuits and brakes-only to find every component working perfectly. Power is reset, the elevator resumes operation, and everything seems fine. Yet the problem strikes again that same evening or a few days later, with no clear root cause. These recurring malfunctions wear on people's patience and make residents lose confidence in the building's safety.
Many maintenance teams jump to conclusions and suspect the drive mainboard, or even replace the entire door operator controller. Still, the trouble continues. The real issue often has nothing to do with the elevator hardware itself-it stems from unstable power supply. Today's elevators rely on sophisticated electronic systems, not basic relay circuits. Their control boards, frequency inverters and communication buses are highly vulnerable to poor power quality. Even a power fluctuation lasting just tens of milliseconds can confuse the control system, activate safety protection and lock passengers inside the car.
Standard multimeters and regular power meters cannot catch these issues. They only measure steady power conditions, while the real trouble comes from transient power anomalies. For instance, When either a water pump, a central air conditioning compressor or a nearby factory press is turned on, the power supply will experience an instantaneous drop in voltage of as much as 15% (below its nominal level) for just over 100 ms. The drop in voltage at the power supply pulls down the voltage of the DC bus within the elevator's inverter, turns on undervoltage protection and causes the elevator to stop. By the time technicians arrive and conduct their routine checks, the grid voltage has stabilized, and there is no evidence of an issue. Other types of disturbances that occur for short periods of time include line-coupled oscillation transients, commutation notches and lightning voltage spikes. All of these disturbances occur in an instant and cannot be detected by traditional methods.
So how do you solve this? Install a dedicated monitoring device at the elevator's main power switch. Use a high-speed power quality logger built to capture transients. It samples voltage waveforms at the microsecond level around the clock. Set up custom trigger rules: start recording if instantaneous phase voltage drops below 90% of the rated value, or capture any voltage pulse exceeding 1.5 times the normal peak. Leave the device running for a week or longer.
The next time the elevator traps people, you won't have to guess. Just pull up the logger's event log to view full waveform data from the exact moment of failure. You'll see how severe the three-phase voltage drop was, how long it lasted, whether oscillations occurred, and how electric current shifted-every detail is fully recorded.
These waveforms reveal the true cause. If every entrapment lines up with a voltage drop greater than 20%, and the timing matches the startup and shutdown cycles of large equipment nearby, you have found the source. You can even pinpoint which heavy load on the same distribution transformer is causing the problem. If the waveforms show obvious commutation notches or strong high-frequency oscillations, nearby thyristor regulators or other inverter-based equipment are emitting harmonics that disrupt the elevator's communication and encoder signals. All data is precise down to the millisecond and exact percentage, far more reliable than guesswork.
This approach turns hidden electrical faults into clear, measurable data. There is no need to randomly swap circuit boards or install generic voltage regulators. With timestamped screenshots and event logs showing exactly when and where the power anomaly occurred, you can map out targeted fixes: install input line reactors, run dedicated power circuits for the elevator, or work with the AC equipment vendor to adjust soft-start settings. One thorough diagnosis delivers a permanent fix.
We designed this power quality logger with transient detection as its core feature, since these brief power disturbances have become a top hidden hazard for smart buildings and industrial facilities. The unit includes internal trigger modules for voltage swells, dips, transient overvoltage, and rapid voltage changes. Running this device does not require detailed understanding of the IEC 61000-4-30 standard. Simply start the onboard elevator fault diagnosis wizard, and it will fine-tune the optimal thresholds that are highly sensitive to elevator control circuits autonomously.
You can check real-time waveforms and event summaries on your phone via Bluetooth. It also supports PQDIF file export for in-depth analysis by power engineers. Compact enough to mount inside a distribution cabinet, this small device acts like a 24/7 electrical heart monitor for your entire building's power system.
