Section 6. Contracts under sections three and four (i) may be for a term or for an indefinite period and shall, unless otherwise provided therein, not be deemed terminated or to have been unauthorized by reason of termination of the New England power pool or of any membership therein or invalidation of any of the provisions of the New England power pool agreement; (ii) may provide for the sale or other disposition of by-products of electric power facilities; and (iii) may contain provisions for arbitration, delegation and other matters deemed necessary or desirable to carry out their purposes. Any party, public or private, desiring to purchase or use by-products of electric power facilities may enter into contracts therefor for short or long terms. Subject to clause (i) of paragraph (1) of subsection (b) of section nine, the obligation of a city or town under contracts referred to in this section shall not be included in the debt of the city or town for the purpose of ascertaining its borrowing capacity.