An attack on the Metcalf power station near Silicon Valley, Calif., in April 2013 was “the most significant incident of domestic terrorism involving the grid that has ever occurred,” said Jon Wellinghoff, who was chairman of the Federal Energy Regulatory Commission (FERC) at the time, in an article published by the Wall Street Journal this week.

After the Metcalf attack, Wellinghoff gave briefings to high-level federal and utility officials, but he’s become frustrated that there have been no arrests, so he’s gone public with his story, citing concern that the nation’s electric-grid isn’t adequately protected against attacks.

Despite the fact that much of the US electric grid sits out in the open, often in remote areas, attacks on the grid are fairly rare. Last August in Arkansas, someone climbed a 100-foot-high transmission tower and severed an Entergy power line alongside a Union Pacific railroad track. Ultimately, the Arkansas attack failed, but there seems to be increasing concern about the security of the power grid. A television series Revolution is based on the premise of life without electricity after a worldwide blackout.

The North American Electric Reliability Corporation (NERC) conducts periodic grid security exercises to prepare the electricity sector to respond to a cyber incident and strengthen utilities’ crisis response functions. But Wellinghoff says he’s more concerned about a physical attack on the grid than a cyber attack.

This week, Wellinghoff was in the news for becoming the strategic counsel of a new trade association, The Advanced Energy Management Alliance (AEMA), which has been formed to advocate for policies that favor demand response.