Updated at 2 p.m.
The track fire at BART's Balboa Park Station early Friday morning that triggered major delays throughout the system was caused by the same kind of equipment failure that prompted the closure of the Walnut Creek station two weeks ago.
On Friday, the blaze slowed down trains to and from the Peninsula.
Agency spokesman Taylor Huckaby said the fire at the Balboa Park stop, located in San Francisco between the Glen Park and Daly City stations, was caused by an electrical arc involving the high-voltage third rail around 4:45 a.m.
A porcelain insulator that covers the third rail caught fire and ignited nearby debris, Huckaby said. The insulators are supposed to prevent electricity that runs through the third rail from grounding and starting a fire, he said.