Despite a two-day blackout in the Back Bay that shuttered businesses and cost some wage-earners their pay, NStar officials said Friday the utility will not pay damages for lost business, income, or food. “If it’s a normal situation, we do not typically, when there is an outage, provide for losses,’’ Thomas May, the top official of the utility, said in an interview. “We do not typically do it for an event that lasts for a day, a day and a half.’’