(a) With respect to any or all customers, if the commission finds that the activities of such person have an adverse effect upon the customers of public utilities furnishing electricity or natural gas and the benefits of such regulation outweigh any adverse effect on the public generally; or
(b) With respect to any customer receiving service not exceeding 500 million British thermal units per year or any residential customer, if the commission finds that such person has engaged in unjust or unreasonable practices with respect to the services or rates available to the customer and the customer has no reasonable alternative to the services provided.
(2) The commission shall not regulate persons under subsection (1)(a) of this section with respect to contracts that became effective prior to the date of service of the complaint or with respect to heating systems already in place on the date of service of the complaint if the commission determines that continued expansion will increase the efficiency of those systems. [1989 c.999 §§4b,4d; 2003 c.82 §6]