INSURANCE

20th Century Ratings Downgraded: Swamped by an estimated $475 million in insurance claims costs from the Northridge earthquake, Woodland Hills-based 20th Century Industries had its financial strength rating downgraded Wednesday by A.M. Best Co. to A- (“excellent”) from A+ (“superior”). The Best downgrade followed similar action last week by Standard & Poor’s, which dropped 20th Century from AA (“excellent”) to BBB+ (“adequate”). Both rating agencies cited 20th Century’s record $256-million first-quarter loss, which reduced the company’s surplus--or cushion against losses--by 42%.