(CNN) -- A power system failure caused an explosion at the University of California Berkeley on Monday, injuring one person and trapping 20 others in elevators, authorities said.
College spokesman Dan Mogulof said the explosion is believed to have been caused by copper wire thieves. Last week, thieves used equipment to dig up and steal copper lines, he said.
Monday night's explosion was in an electrical vault and appeared to be related.
The power went out on campus about 4:30 p.m. local time (7:30 p.m.). Two hours later, an explosion went off on the north side of California Hall, he said.
The campus was closed, and students and staff cleared.
One person was taken to a hospital with minor injuries, Mogulof said. Authorities found 20 people trapped in elevators around campus.