PLYMOUTH, Mass. — The Pilgrim nuclear power plant in Plymouth remains off line a day after it was shut down because of a problem with the electrical system that runs the pumps that supply cooling water to the reactor core.

A spokeswoman for the Pilgrim Nuclear Power Station’s owners said the plant remains off line Friday morning, after being shut down at about 8 a.m. Thursday.

The Nuclear Regulatory Commission says it appears as if the main feedwater power supply breaker tripped.

The NRC and plant operators said there was no threat to public safety.

Pilgrim owner Entergy said backup pumps automatically activated and plant systems performed as designed.

The cause of the fault is under investigation and there is no timetable for the plant to restart.