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A fleet vehicle makes its way into the the Hydro One Claireville Transfer Station in Vaughan, Ontario Monday March 9, 2015.Tim Fraser/The Globe and Mail

The mystery of the flickering lights that affected residents across Ontario has been solved.

According to Hydro One, contact between two transmission lines caused the flicker Monday night that prompted confusion across the province.

Residents from areas including Toronto, Ottawa, Waterloo and Richmond Hill took to social media Monday night to report the flickering, which occurred at 9:26 p.m. At the time, Hydro One had no explanation for the occurrence.

They confirmed Tuesday afternoon that an insulator, which holds transmission lines off transmission towers, broke.

This caused a transmission line to fall to the ground, hitting another transmission line along the way, causing the flicker.

Hydro One is still investigating what caused the insulator to break, and whether or not salt contamination or the weather could have anything to do with it, says Tiziana Baccega Rosa, spokesperson for Hydro One.

Reza Iravani, an electrical and computer engineering professor at the University of Toronto, says that the touching of the two transmission lines created a flicker across Ontario because the contact between the lines caused a fluctuation of voltage.

He says that any change to Hydro One's system that creates a fluctuation of voltage beyond the limit that the system expects can cause flickering.

Another example of a large change could be a large industrial unit, such as a mining system, suddenly switching on. The mining system would absorb a substantial amount of energy, and cause a change in Hydro One's system, says Mr. Iravani.

Usually, Hydro One is aware of large consumers of energy, and has countermeasures set in place to "counteract" the voltage change as the large energy consumer turns on or turns off, Mr. Iravani says.

"[Monday night's incident] is a scenario that cannot be predicted," he says. "As a result, there's no countermeasure system in place to mitigate that change."

The incident occurred in Etobicoke, near Hydro One's Richview Transformer Station, a press release states.

Ms. Baccega Rosa says there were no power outages caused by the incident.

Meanwhile, thousands in the Greater Toronto Area were hit with unrelated power outages Monday evening and Tuesday morning.

At around 8:30 Monday night, Toronto Hydro began to report outages in the city. At its peak, 5,000 customers were affected, says spokesperson Tori Gass. There are 200 customers still left without power, she says.

This morning, PowerStream also reported 8,400 customers without power in Barrie, and around 1,000 in Vaughan. Power has been restored in both cities, according to PowerStream's Twitter page.