Four people suffered minor burns. One of them was treated at a hospital and released. The explosion occurred in an underground utility vault outside California Hall as crews were trying to restore power on campus shortly before 7 p.m.
With many buildings in the dark, fire crews also freed about 20 people stuck in dormitory elevators as a result of the outage that also led to the mandatory evacuation on campus.
Officials say it may have been caused by a theft of underground copper wire last week from an electrical substation.
The visible damage was repaired over the weekend, but it may have been more extensive than they thought.
The Associated Press contributed to this report.