The lift system is designed to work well only when the power supply is stable (it means that the power supply system has to be the infinite bus system). It is quite common that the lift maybe not recovery itself after incoming power supply has resumed if it has detected any abnormal situation/behavior in the drive system which resulting from the power surge (usually the surge will happen when power supply ON or OFF) e.g.
1. Voltage surge
2. Current surge
3. Speed difference
4, etc
When the lift blockage from above factors it requires to do a manual reset by lift engineer to ensure that the lift is still in the good condition and safe for normal operation.
The highest chance of lift blockage from power supply failure is when the the lift running on full speed because the control system is monitoring the behavior of voltage, current and speed of the drive system and if anything go wrong the lift control system will shutdown the lift from normal operation to prevent a serious damage on the drive system and other related components.