Nearly 4,000 Pacific Gas & Electric customers are without power in Menlo Park following a widespread outage in San Mateo County late this morning.

About 21,000 customers lost power earlier in the day when a metallic wire used to support a transmission tower touched an overhead transmission line at 11:45 a.m. in or near Los Altos or Stanford, according to Pacific Gas & Electric Corp. spokesman Joe Molica.  Crews working on the problem brought the number of affected customers down to 3,900 by the afternoon.

“Anytime anything metallic comes into contact with a transmission line, that particular line will shut itself off as a safety precaution,” Molica said. “Repairs are being made now.”

PG&E is still working to restore power to 3,900 Menlo Park customers, many of whom are located along Santa Cruz Avenue and Alpine Road, according to Molica.