That conclusion has been supported by the operator of Spain’s national grid, Red Eléctrica, which has located where outages began on Monday. Two separate incidents of power outages led to instability in the grid leading to a “breakdown in interconnections with France,” leaving the Iberian grid isolated.

It was the second serious European power outage in less than six weeks after a March 20 fire shut down Heathrow Airport in the U.K.