2006 New York Code - Power Source.

 
    § 27-384 Power source. (a) Where a total of more than four exit and/or
  directional  signs  is  required,  the  signs  shall  be connected to an
  emergency power source or  to  storage  battery  equipment  meeting  the
  requirements  of  the  commissioner, provided, however, that in existing
  buildings, the signs may be on  circuits  that  are  separate  from  the
  general lighting and power circuits, taken off ahead of the main switch.
    (b) Existing high rise buildings classified in occupancy group C, D or
  H  and  existing  buildings  classified  in  occupancy group E, G or J-1
  (except for "residential  hotels,"  as  such  term  is  defined  by  the
  commissioner  pursuant  to  rules and regulations) shall comply with the
  requirements of this section on or before April first, nineteen  hundred
  eighty-seven.
    (c)  Notwithstanding the foregoing, in the existing buildings required
  to comply with subdivision (b) of this section, all such  existing  exit
  and/or  directional signs on circuits taken off ahead of the main switch
  shall be connected to an emergency power source or  to  storage  battery
  equipment meeting the requirements of the commissioner on or before July
  1, 2007.