Hongkong Electric (HKE) said on Monday that a blunder that plunged parts of Hong Kong Island into darkness last month could have been avoided if adequate documentation on electrical circuits had been in place.

During routine maintenance at the power company's Cyberport station on 19 April, an engineer inadvertently ran electricity to an undocumented backup cable without verifying that it was connected to the circuit.

HKE submitted an investigation report on the outage on Monday, which said the power disruption lasted for up to 48 minutes and affected about 44,000 customers.

That means under its current Scheme of Control Agreements, the power company can earn a reward of 0.015 percent of earnings for restoring the power in less than 65 minutes, even though it was responsible for the outage.

Francis Cheng, HKE's operations director, refused to comment on the reward mechanism or confirm whether affected customers would receive compensation.

The government has urged the company to use any reward to compensate households hit by the blackout.

Cheng said the engineer responsible conducted an on-site inspection as required. However, he said the bottom of the cable connection tank was covered, and the engineer was not "alert" enough to ensure that the backup cable was connected to the circuit.

But he also admitted that adequate documentation of the electrical circuits would have prevented the power outage.

“We know that if he [the engineer] is not sufficiently aware enough, we can use site labels to improve the situation,” Cheng said.

“We can use the circuit diagram to make it clearer so that everyone at the site will instantly know that there are spare cables connected,” he added.

He added that the engineer involved has been reassigned to the support team to "regain confidence," and that he will have to pass an assessment before returning to his original duties.

Cheng said all the four spare cables have been disconnected for the time being.

“But if we have to completely segregate the cable from the switch gear, we have to have some spare parts from the manufacturers. So to complete that part, we have to wait for the spare part. And our expected completion date is July,” he said.

A general manager, Ip Sung-tai, said HKE will pause all related projects until new guidelines are formulated, spare cable labels are added, and the energy management system circuit diagram for engineers is updated.

He added that more resources will be allocated to inspect the critical infrastructure of the company's transmission network, with engineers required to double-check before conducting maintenance work.