Suffolk County Police Arson Squad detectives say the fire that forced 15 residents of a Holbrook condo complex out of their homes the day before Christmas started after a Friday fire at the same complex rekindled.

Detectives say the Friday fire started about 3:45 p.m., probably because of an electrical “event” between floors at the Woodgate Village Condominium on Springmeadow Drive.

That fire affected only one unit. But the fire that rekindled 3:50 a.m. Saturday in the ceiling of the complex spread to two units and forced authorities to shut off electricity in six more.

The fire forced families to alter holiday plans, but some said they were focusing on how no one was injured and how the fire could have been more destructive.

Several fire departments responded and extinguished the blaze, authorities said.

Eight families were displaced and assisted by the Red Cross, said Red Cross volunteer spokeswoman Jessica Kirk. The group includes six children.

The Red Cross early Saturday provided housing for three or four of the families, said Craig Cooper, spokesman for the American Red Cross on Long Island. A poodle named Cupcake also was housed, he said.

“It’s heartbreaking any day,” Cooper said of the fire and displacement. “It’s even more frustrating when it’s the day before Christmas.”

The charity “is prepared to provide overnight support again if needed,” he said.

All eight families were given debit cards to buy clothing and other necessities, he said.

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Police said Sunday morning that the cause of the fire remained under investigation, but that authorities believe it was accidental.

Islip Town spokeswoman Caroline Smith said earlier that the fire marshal’s office was investigating both fires.

Complex management did not immediately return a call seeking comment Sunday morning.