On June 24, 2013, at 9:20 PM PDT, Diablo Canyon experienced a loss of offsite power to the startup transformers of both units due to a failure on the 230 kV transmission system. At the time, none of the startup transformers were loaded as both units were online and their electrical systems were at the time being powered by the plant's turbine generators. However, the emergency diesel generators were started with no load during the outage as a precaution in case either unit tripped offline while offsite power was unavailable. The electrical output of the plant via the 500 kV transmission system was not interrupted, allowing both units to remain online during the outage.