Section 120. Board of contract and supply

There  shall  be  a board of
  contract and supply, composed of the mayor, comptroller, commissioner of
  public works, corporation counsel and city engineer. Except as otherwise
  provided by law, it shall be the duty of such board, after public notice
  and in accordance with regulations to be prescribed by general ordinance
  of the common council, to let  to  the  lowest  bidder,  who  will  give
  adequate  security  therefor,  all  contracts for the performance of any
  work or for the supply of any material required by or for the use of any
  officer, board, body or department of the city, in all cases  where  the
  expense of such work or materials, or both, shall exceed the sum of five
  hundred  dollars, unless by ordinance of the common council adopted by a
  vote of not less  than  four-fifths  of  all  the  members  thereof  and
  unanimously  approved  by the board of estimate and apportionment, it is
  determined that a public emergency exists in which case  said  ordinance
  shall  state  the  circumstances  and conditions that created the public
  emergency, which shall be limited to those arising out of an accident or
  other unforeseen occurrence or  condition  affecting  public  buildings,
  public  property  or  the  life,  health,  safety  or  property  of  the
  inhabitants of such city require immediate  action  which  cannot  await
  public  bidding, and shall designate the officer, board or department to
  procure such  work  or  purchase  such  materials.  In  case  of  public
  emergency  involving  accident  or  other injury by which the heating or
  plumbing of  any  of  the  public  buildings  or  any  of  the  fire  or
  water-works  apparatus  or any of the machinery used in sewage-treatment
  plants,  or  for  garbage  disposal,  or  any  equipment  used  by   the
  water-works  or  department  of  public works shall become disabled, the
  commissioner having jurisdiction thereof shall cause repairs thereto  to
  be  made  without  a  letting by contract, upon filing with the board of
  contract and supply a certificate, approved by the mayor,  showing  such
  emergency and the necessity for such repairs. The board shall have power
  to  reject  all  bids  or  proposals if in its opinion the lowest bid or
  proposal is excessive. The said  notice  shall  describe  the  work  and
  materials for which contracts will be let and the day and hour and place
  of  the meeting of the board at which proposals therefor will be opened.
  Specifications for the performance of any work and for the supply of any
  materials shall be prepared and set forth  with  sufficient  details  to
  inform  all  persons proposing to bid therefor of the nature of the work
  to be done and of the materials to be supplied, and written  or  printed
  copies  thereof  shall  be  delivered  to all applicants therefor. Every
  contract for a public improvement shall be based upon an estimate of the
  whole cost  thereof,  including  all  expenses  incidental  thereto  and
  connected  therewith,  to  be  furnished by the proper officer, board or
  department having charge of such improvements. No bid or proposal  shall
  be  received  or contract awarded, other than for a local improvement or
  work to be performed by the city, which  involves  the  construction  or
  maintenance  of  any  structure,  erection,  obstruction  or  excavation
  within, under, over, along or upon any street or public place within the
  city, unless the person to whom such contract  shall  be  awarded  shall
  have a franchise permitting the same.