The state Public Utilities Regulatory Authority has approved Connecticut Light & Power’s $300 million plan to strengthen its poles, lines, and other infrastructure against large weather events, authorities say. 

The improvements were required as part of the merger agreement between CL&P parent Northeast Utilities and Boston-based NStar, CL&P said Wednesday.

The condition arose after Tropical Storm Irene and the October 2011 nor’easter separately knocked out power to the majority of CL&P customers, some for up to 11 days.

The system resiliency plan approved by PURA focuses on enhanced tree trimming to prevent downed branches from falling onto wires; using thicker-coated wires; and using stronger poles, crossarms, and other electrical equipment. 

The advanced tree trimming work has already begun, with CL&P investing $32 million to expand the program this year. The thicker wires will be installed next year, and the remaining work will begin this spring.