Attack on electric grid raises alarm

Shooters armed with assault rifles and some knowledge of electrical utilities have prompted new worries on the vulnerability of California's vast power grid.

A 2013 attack on an electric substation near San Jose that nearly knocked out Silicon Valley's power supply was initially downplayed as vandalism by Pacific Gas & Electric Co., the facility's owner.

Gunfire from semiautomatic weapons did extensive damage to 17 transformers that sent grid operators scrambling to avoid a blackout...

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