Thousands of Molokai residents were without power for more than seven hours Sunday night and early Monday morning after an islandwide power outage that began at 10:04 p.m., Maui Electric Co. officials said.
The initial cause of the outage was a pole top fire at the Palaau substation that appeared to have started from a contaminated insulator, said MECO spokeswoman Kau'i Awai-Dickson.
"Over time, insulators that hold the electric line to the pole can become soiled by salt spray and dust," she said. "When light rain falls on a contaminated insulator, the rain water creates a path from one end of the insulator to the other, causing an arc that can result in a fire."
The fire triggered a fault on the electric lines that "resulted in a sudden drop in frequency, which set in motion an automatic generation load shed," she said.
A load shed is a safety mechanism that protects the electrical system during severe disruptions by turning off power to some customers.
In Molokai's outage, the result was an islandwide outage.
Overall, 3,156 customers were affected by the blackout, an official said. Power was restored to residents incrementally, with the first customers getting power back on at 5:13 a.m., or after seven hours and nine minutes without power.
The last customers had their power returned at 6:28 a.m., or after eight hours and 24 minutes.
Awai-Dickson said MECO crews worked through the night to replace the burned pole and make repairs.