A. Unless exercised within a period designated by the commission, exclusive of any delay due to the order of any court, authority conferred by a certificate of convenience and necessity issued by the commission shall be void. The beginning of the construction of a plant or system, in good faith, within the time prescribed by the commission and the prosecution of the same with reasonable diligence in proportion to the magnitude of the undertaking, shall constitute an exercise of the authority.

B. The holder of a certificate shall render continuous and adequate service to the public and shall not discontinue, reduce or impair service to a certificated area, or part of a certificated area, except ordinary discontinuance of service for nonpayment of charges, nonuse and similar reasons in the usual course of business, unless and until there shall first have been obtained from the commission a certificate that neither the present nor future public convenience and necessity will be adversely affected thereby; except that the commission may, upon appropriate request being made, authorize temporary or emergency discontinuance, reduction or impairment of service, without regard to the provisions of this section; provided, however, that nothing in this section shall be construed as requiring a certificate from the commission for any installation, replacement or other changes in plant, operation or equipment which will not impair the adequacy or quality of service provided.