The U.S. electric system is in danger of widespread blackouts lasting days, weeks or longer through the destruction of sensitive, hard-to-replace equipment. Yet records are so spotty that no government agency can offer an accurate tally of substation attacks, whether for vandalism, theft or more nefarious purposes. ... Most substations are unmanned and often protected chiefly by chain-link fences. Many have no electronic security, leaving attacks unnoticed until after the damage is done. Even if there are security cameras, they often prove worthless. In some cases, alarms are simply ignored. ... the Federal Energy Regulatory Commission, which regulates the country’s interstate power system, began requiring that utilities better protect any substation that could disable parts of the U.S. grid if attacked. ... FERC’s new rule, however, doesn’t extend to tens of thousands of smaller substations ... The grid was cobbled together during the electrification of the U.S. over the past 125 years. It is a fragile, interdependent system generally more vulnerable in summer when it is running closer to its limits. It is also at risk during low-demand periods, when power-plant operators and linemen perform maintenance. Fewer plants and transmission lines operating mean fewer options for delivering electricity during emergencies.