Section 115. Public letting of contracts

The  commission  is  hereby
  authorized, whenever it is  of  opinion  that  the  public  interest  so
  requires,  to  direct  any public utility subject to the jurisdiction of
  the commission to award contracts or agreements  for  the  construction,
  improvement  or  extension  of  its plant, works or system, exceeding in
  amount twenty-five thousand dollars in any calendar year, to the  lowest
  responsible  bidder,  after  a  public  offering has been made and after
  advertisement and notice of such  offering  have  been  given,  and  the
  commission   may  prescribe  rules  and  regulations  relative  to  such
  advertisement, notice and public letting.