table   6-1.   Neutral   polarity,   where   it   exists,   is identified by the white conductor. Isometric  Wiring  Diagram An isometric wiring diagram is supplied for each shipboard electrical system. If the system is not too large,  the  diagram  will  be  on  one  blueprint  while  larger systems may require several prints. An isometric wiring diagram shows the ship’s decks arranged in tiers. It shows bulkheads and compartments, a marked center- line, frame numbers usually every five frames, and the outer edge of each deck in the general outline of the ship. It shows all athwartship lines at an angle of 30 degrees to the centerline. Cables running from one deck to another are drawn as lines at right angles to the center- line. A single line represents a cable regardless of the number of conductors. The various electrical fixtures are identified by a symbol number and their general location is shown. Therefore, the isometric wiring dia- gram shows a rough picture of the entire circuit layout. "Figure   6-2   (four   pages   at   the   end   of   this chapter)   shows   an   isometric   diagram   of   a s e c t i o n    o f    t h e    s h i p ' s    s e r v i c e    a n d emergency   lighting   system   for   a   DLG."   This figure shows the forward quarter of the decks con- cerned, whereas the actual blueprint will show the entire decks. Note the reference to another isometric diagram at the top of the figure. It shows that the diagram of the complete  lighting  system  for  this  ship  required  two blueprints. All electrical fittings and fixtures shown on the isometric wiring diagram are identified by a symbol number as stated previously. The symbol number is taken  from  the  Standard  Electrical  Symbol  List, NAVSHIPS 0960-000-4000. This publication contains a  complete  list  of  standard  symbol  numbers  for  the various  standard  electrical  fixtures  and  fittings  for  ship- board applications. For example, look at the distribution box symbol 615 located on the second platform star- board  at  frame  19  (fig.  6-2).  It  is  identified  in NAVSHIPS 0960-000-4000 as a type D-62A four- circuit  distribution  box  with  switches  and  midget  fuses. Its federal stock number is 6110-152-0262. Cables shown on the isometric wiring diagram are identified by the cable marking system described earlier in this chapter. In addition, cable sizes are shown in circular mils and number of conductors. Letters show the number of conductors in a cable; S for one-, D for Table 6-1.—Color Code for Power and Lighting Cable Conductors System 3-phase  ac No. of Conductors in Cable 3 2 2 2 Phase of Polarity A B C AB BC AC Color Code Black White Red A,  black B, white B, white C,  black A,  black C,  white 3-wire  dc 3 2 2 2 + +/- + and +/- +/- and - + and - Black White Red +, black +/-,  white +/-,  white -, black +, black -,  white 2-wire  dc 2 + Black White 6-4