Starting in May , National Grid customers will start getting relief from soaring electric rates.The Department of Public Utilities announced Tuesday that it has approved basic service rate reductions that will lead to a roughly 40 percent reduction in a typical residential customer's monthly bill. The utility serves nearly 1.4 million electric customers."The Department knows that these rate reductions will provide much-needed relief to families and businesses," DPU Acting Chair Cecile Fraser said in a statement. "We continue to work with utilities and stakeholders to help transition our energy supply to clean energy sources at a stable and affordable cost."The approval came quickly. National Grid filed its summer rate adjustment last week, projecting it would drop the bill for a typical residential customer by $115.39, from $297.22 to $181.83.The utility warned that summertime bills will be higher than last year, even after the rate reduction, and said lower demand for natural gas in the summer helps bring rates down.National Grid's basic service rates change each year on May 1 and November 1.