Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

An abrupt loss of power generation at a substation in Granada, followed by failures seconds later in Badajoz and Seville, triggered an unprecedented blackout across Spain and Portugal on April 28, Spain's energy minister said on Wednesday.

An abrupt loss of power generation at a substation in Granada triggered an unprecedented blackout across Spain and Portugal, authorities said.