HK Electric said a voltage dip happened on Thursday morning during a fault with an interconnection circuit between the company and CLP Power and apologised for any inconvenience caused.

While supply voltage resumed as normal immediately after the incident at 9.22am, HK Electric said electrical appliances such as lifts, computers, air-conditioning systems, etc that are sensitive to voltage changes might be affected.

"After the voltage is back to normal, it may require the responsible electrical personnel to reset the affected appliances and restore them to normal operation," it wrote on its website.

The firm, which serves Hong Kong Island and Lamma, did not specify the affected locations and number of customers.

Meanwhile, the Fire Services Department received around 100 reports of people trapped in lifts on Hong Kong Island between 9am and 10am.

Electrical and building services engineer Ho Wing-ip said the circuit in question is designed to offer mutual support among the two power companies in emergency situations.

He told RTHK that the interconnection's protection mechanism is activated when there is a fault along the line.

"The system's protection mechanism instantly disconnects that line to prevent the damage from spreading or affecting respective grids. The end result is a momentary [voltage] fluctuation," Ho said.

"However, some equipment like lifts and fire alarm systems are highly sensitive to voltage change. Even such a brief fluctuation could trigger the protection mechanism and stop them from operating."


Edited by Thomas McAlinden