PITTSBURGH—Three dorms that lost power at Duquesne University in Pittsburgh on Thursday have reopened—but they will again be without power for several hours, this time due to a planned outage.

About 1,300 students at the private, Catholic school were forced to stay off-campus, with friends in other residence halls, or in temporary spaces equipped with cots in other university buildings after the outages at St. Ann, St. Martin and Assumption halls.

The dorms reopened Sunday, but school officials say all three will lose power from 10 a.m. to 3 p.m. Monday so crews can switch from backup generators back onto the newly repaired power system.

The power failed after a circuit breaker on a gas compressor at the school's on-campus energy center failed and workers traced the problem to a faulty underground cable.