It could be several days before Maritime Electric knows why the power went out for about 20,000 customers on P.E.I. Wednesday morning, the utility said Wednesday

The blackout started at 9:21 a.m. AT, affecting parts of Charlottetown — the downtown and the University of Prince Edward Island  — and from the capital east across the north of the province to East Point.

The power came back on gradually, and the blackout ended entirely a little more than an hour after it started.

Officials with the power company say they still don't know what happened.

"It did originate at UPEI," said Kim Griffin, Maritime Electric spokeswoman. "We know that some of the problem happened on one of the lines there.

"But what we believe happened is that the problems at UPEI also triggered our system to protect itself. So basically the transmission line started to shut itself down from Charlottetown to East Point to protect itself thinking that there was a major problem in the city.