(Reuters) -Britain's National Grid said on Monday it had filed a three-year rate plan proposal with the New York Public Service Commission for its upstate New York electric and natural gas distribution business.

Niagara Mohawk Power Corporation ( NMPWP ) , which serves 1.7 million electric and 600,000 gas customers, represents around 15% of National Grid's regulated asset base.

If the proposed plan is approved, residential electricity customers using an average of 625 kilowatt-hours (kWh) per month would see monthly bills rise by $14.32 in the first year, $6.44 in the second, and $4.34 in the third. 

Residential natural gas customers using an average of 78 therms per month would see monthly bills rise by $7.66 in the first year, $8.08 in the second, and $9.18 in the third, the company said.

The plan, which will run from May 2025 to March 2028, includes a return on equity of 9.5%, and capital investment of $1.43 billion in electricity and $351 million in gas for NIMO in the first rate year, National Grid said.

It also includes more than $290 million in bill discounts, and retirement of about 112 miles (180 km) of leak-prone natural gas pipe in the next three years, the company added.

A final decision from the commission is expected in the next few months.