Florida Power & Light Co. has announced preliminary findings of its ongoing investigation into the cause of an outage affecting approximately 584,000 customers on Tuesday, Feb. 26.

While still preliminary, the results of the investigation so far indicate that human error was the primary factor immediately responsible for the event, which began at 1:08 p.m. Eastern Time.

A field engineer was diagnosing a switch that had malfunctioned at FPL’s Flagami substation in west Miami. Without authorization, the engineer disabled two levels of relay protection. This was done contrary to FPL's standard procedures and established practices. Standard procedures do not permit the simultaneous removal of both levels of protection.

During the diagnostic process, a fault occurred and, because both levels of relay protection had been removed, caused an outage ultimately affecting 26 transmission lines and 38 substations. One of the substations affected serves three of the generation units at Turkey Point, including a natural gas unit as well as both nuclear units, which, as designed, automatically and safely shut down due to an under-voltage condition. Also affected were two other generation plants in FPL’s system. Total impact to the system was a loss of 3,400 MW of generating capacity.

“First, I want to reiterate my apology to our customers and the communities we serve. We understand that this event caused a significant inconvenience. We also understand that reliability and safety are cornerstones of our commitment and accountability. While in this instance we failed to perform to our expected standards in regard to reliability, safety was never an issue and the safeguards built into our system worked as intended. Because of this, and the experience, training and practice drills of our work force, we were able to restore power to our customers quickly,” FPL President Armando Olivera said.

“These preliminary findings address the most pressing questions that have been posed. We are committed to completing a full and thorough investigation, to cooperating fully with the appropriate regulatory agencies and to sharing our findings publicly when the investigation is completed. We will address any issues that are identified in order to prevent a recurrence,” Olivera said.

"While the investigation is ongoing, to this point we have no indication that there are any deficiencies with the design of our facilities or with our maintenance procedures. However, out of an abundance of caution, we have implemented interim changes governing relay protections to prevent a recurrence," Olivera said.

The final account of customers affected by this incident totals 584,000 customers, or 13 percent of FPL’s total. Of these, 66 percent had power restored within an hour, 90 percent within two hours and virtually all customers whose service was affected by this event had service restored by 4:30 p.m. Some FPL customers who participate in On Call, a program that cycles off major appliances during peak demand, did not have their appliances turned back on for as many as several hours thereafter.