I am not sure what to think of this one. It occurred around the time of the Boston Marathon attack, but does not appear to be linked. It took a little while for the news to percolate to a national level.
Sounds sort of Uni-Bomber-like to me, but within a group setting.
Shane Harris, Foreign Policy, 27 December 2013 (hat tip: NC)
Around 1:00 AM on April 16, at least one individual (possibly two) entered two different manholes at the PG&E Metcalf power substation, southeast of San Jose, and cut fiber cables in the area around the substation. That knocked out some local 911 services, landline service to the substation, and cell phone service in the area, a senior U.S. intelligence official told Foreign Policy. The intruder(s) then fired more than 100 rounds from what two officials described as a high-powered rifle at several transformers in the facility. Ten transformers were damaged in one area of the facility, and three transformer banks -- or groups of transformers -- were hit in another, according to a PG&E spokesman...
"These were not amateurs taking potshots," Mark Johnson, a former vice president for transmission operations at PG&E, said last month at a conference on grid security held in Philadelphia. "My personal view is that this was a dress rehearsal" for future attacks.
Having done a little work around utility systems, I can second the articles comments that this is not the work of neophytes to the power grid.