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INTERIOR ELECTRICAL WIRING   SYSTEM
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Engineering Aid 3 - Beginning Structural engineering guide book
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Figure  9-9.—Underground  service  to  building. transformer   to   the   junction   box   and   to   the service    equipment. Service  Entrance The  starting  point  for  interior  wiring  is  the SERVICE  ENTRANCE,  which  brings  power from the service conductors to the service equip- ment. Refer again to figure 9-8. As shown in this figure,   the   service   entrance   conductors   are connected   to   the   service   drop   at   a   point   just outside   the   building.   These   conductors   may be   approved   single   conductors   run   through a   protective   raceway,   such   as   rigid   metallic or   nonmetallic   conduit.   The   service   entrance conductor   may   also   be   an   approved   type   of service  entrance  cable  that  does  not  need  raceway protection  unless  it  is  likely  to  be  damaged  by abrasions or from being struck by passing equip- ment.   Where   single   conductors   are   used,   they must  be  insulated  as  require  by  the  NEC®.  The NEC®  also  specifies  the  size  wire  that  may  be  used as  service  entrance  cable. Also  shown  in  figure  9-8  is  a  SERVICE HEAD.   A   service   head,   frequently   called   a WEATHERHEAD,  is  used  with  a  raceway  to provide  an  entrance  for  the  conductors  into  the building. The weatherhead is designed to prevent the  entrance  of  rain  into  the  raceway.  It  is  also designed  to  reduce  abrasion  to  the  insulation. A  SERVICE  ENTRANCE  SWITCH  (left- hand   side   of   fig.   9-10)   provides   a   means   of brings  the  power  to  the  building,  are  called  the service  lateral.  Sometimes  these  conductors  are tied to an overhead distribution system, and they run  down  the  pole  into  the  ground  before  they are run to the building. In other cases, the entire distribution  system,  except  for  the  transformers, is  underground.  The  service  lateral  may  be connected to a secondary main, or, if the building is served by separate transformers, it is connected to  the  transformers. The  service  lateral  may  be  installed  in  rigid conduit,  either  metallic  or  nonmetallic,  or  it  can be  installed  with  underground  service  entrance (USE)  cable.  The  figure  shows  the  layout  of  an underground   service   lateral   run   from   the Figure 9-10.—Typical layout for entrance switch, lighting panel, and power panel. 9-7







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