SONOMA COUNTY, Calif. (AP) — Investigators say a deadly 2017 wildfire that killed 22 people in Northern California wine country was caused by a private electrical system, not equipment of embattled Pacific Gas & Electric Co.

The state's firefighting agency said Thursday that the fire started next to a residence. The agency did not find any violations of state law.

The fire was one of more than 170 fires that torched the state in October 2017. It destroyed more than 5,600 structures over more than 57 square miles (148 sq. kilometers) in Sonoma County.

The cause came as a relief to PG&E, which plans to file for bankruptcy protection next week, citing billions of potential damages from other deadly and destructive wildfires.

CalFire did not immediately release its full fire cause report.