Electrical power equipment owned by California’s largest utility company appeared to have malfunctioned in an area where the state’s deadliest wildfire started last week, according to a PG&E Corp. securities filing.

The cause of the Camp Fire, which has burned through some 117,000 acres in Northern California’s Butte County, remains under investigation. At least 42 people have died in the fire and more than 6,500 houses have been destroyed, officials said.