Mike Nicoloro, the wiring inspector for the city of Cambridge, said the explosion could have been caused by a variety of causes, from an aging electrical cable to an abnormally high demand for electricity from the surrounding buildings.
"It's cold today, and all the heating units are running," Nicoloro said.
By 2:30 p.m., the fire trucks were gone, but work was just beginning to fix the electrical problem.
Crews from NSTAR worked well into the night, re-routing power so that workers could repair the burned cable.
Wicks was concerned that repairs might prove so difficult that all of Harvard Square would lose power.
"This whole area could be knocked out," he said. "But we can't tell until we get down there."
But as of 7:30 p.m. yesterday, NSTAR workers said power had been successfully re-routed, and they did not expect any significant interruptions in service as they repaired the damaged cable.
--Staff writer Joyce K. McIntyre can be reached at jmcintyr@fas.harvard.edu.