BOSTON (WHDH) - A faulty power cable is to blame for the significant delays that snarled commuters on three subway lines during the evening commute on Friday, MBTA General Manager Steve Poftak said Monday.

A power cable near Causeway Street in Boston’s North End failed, creating signal problems across the system just as thousands of commuters were heading home for the weekend.

Trains on the Orange, Blue, and Green lines experienced delays of up to 30 minutes. Payment kiosks were rendered nonfunctional, some stops were in the dark, and T workers had to manually waive trains into stations.

Normal service was restored around 8 p.m.

Poftak said plans are in motion to make sure Friday’s “challenging evening commute” doesn’t happen again.

“It’s not an ideal situation for us,” Poftak said. “We know folks were inconvenienced.”

Resources have been put aside to implement a $170 million upgrade to the agency’s power systems, according to Poftak.

Work is expected to be completed by the summer.

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