For the purpose of enabling the commission and the department of energy to perform their duty to keep informed as provided in N.H. Rev. Stat. § 374:4, every public utility, before making any addition, extension, or capital improvement to its fixed property in this state, except under emergency conditions, shall report to the commission and the department of energy the probable cost of such addition, extension, or capital improvement whenever the probable cost thereof exceeds a reasonable amount to be prescribed by general or special order of the commission. For this purpose, the commission may classify public utilities according to the amount of their respective fixed capital accounts, and prescribe a reasonable limitation for each such classification. In no case shall the minimum amount prescribed be less than
1/4 of one percent of such fixed capital account as of December 31 of the preceding year, or $10,000, whichever is the smaller amount. Reports shall be filed in writing within such reasonable time as may be prescribed by the commission before starting actual construction on any addition, extension, or improvement. The commission shall have discretion to exclude the cost of any such addition, extension, or capital improvement from the rate base of said utility where such written report thereof shall not have been filed in advance as herein provided.