Lightning caused both power outages in Porter Creek and beyond Thursday evening, officials have confirmed.

Meanwhile, Yukon Energy crews are still trying to determine why the largest hydro unit at the Whitehorse Rapids Dam went down early this morning, triggering a grid-wide blackout except in Mayo.

Yukon Energy spokeswoman Janet Patterson said Mayo stayed powered up because of protection features built into the system.

Everybody else lost power just before 2 a.m.

Yukon Energy and ATCO Electric Yukon crews had power to the grid fully restored by 6:13 a.m., she said.

“Whitehorse unit number four should be online very soon,” Patterson said in an interview late this morning.

“They are working on it right now.”

Patterson said the crews are trying to determine if the two outages caused by lightning strikes Thursday evening had anything to do with the failure of unit number four this morning.

The fourth wheel, as it’s commonly referred to, has a generating capacity of 20 megawatts, accounting for half of the total hydro capacity at the dam.

As result of the fourth wheel going down, Patterson said, four backup diesel generators at the dam and one of the new LNG units were fired up to augment generation by the three other hydro units.

All three diesel units in Dawson were also brought on line as well as one in Faro, she said.

Patterson pointed out the Aishihik hydro facility is unavailable because the 40-year-old elevator that moves staff from the surface to the generating floor 110 metres below is being replaced.

Carla Howard of ATCO Electric said this morning the first outage yesterday occurred at 5:53 p.m. Thursday when lightning struck in the Kulan industrial area, affecting some 2,400 customers in Porter Creek.

Power was fully restored an hour later, she said.

At 7:45 p.m., however, another lightning strike on a Yukon Energy line jarred ATCO’s distribution system and caused a second outage in Porter Creek. Power to ATCO customers was fully restored by 8:33.

Patterson said the second strike knocked out power all along the transmission line running north to Carmacks, and to the Minto Mine.

But those customers were restored within 15 minutes, she said.

Patterson said the lightning strike tripped a breaker, and when crews tried to re-energize, it held.