4(1)The Board shall, when approving or fixing just and reasonable rates and tariffs under section 52 of the Act for each class of customers, adopt the cost of service method or technique, with a revenue to cost ratio not exceeding 1.2:1 for any class of customers, provided that the rates and tariffs for any class of customers shall not exceed the rates and tariffs that would apply to that class of customers if determined through the application of the market based method or technique.