PIEDMONT -- A fire that broke out at the Ace Hardware on Grand Avenue early Sunday morning caused about $20,000 in damage and temporarily closed the business along the city's Oakland border.

The fire was confined to a rear storage room at the store, which reopened Monday, and was likely caused by an electrical malfunction, Piedmont fire Chief Bud McLaren said. No one was hurt.

The fire tripped a security alarm about 4:15 a.m. and when police officers responded they found smoke coming from the rear of the business at 1221 Grand Ave. The fire also set off the store's sprinkler system, which helped minimize the damage, McLaren said.

The firefighters who forced their way into the building found most of the damage was near an electrical panel, which was also filled with water from the sprinkler, the chief said.

Two Piedmont fire engines and a paramedic responded.

As part of a mutual aid agreement between the cities of Piedmont and Oakland, the Oakland Fire Department provided two engines, a truck and a battalion chief.

Piedmont fire Capt. Jon Fitzpatrick was in charge at the scene.

Reach Peter Hegarty at 510-748-1654 or follow him on Twitter.com/Peter_Hegarty.