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Fixture Symbols
Overhead Power Distribution

Engineering Aid 3 - Beginning Structural engineering guide book
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CHAPTER 9 ELECTRICAL SYSTEMS AND PLAN It is important for an EA working on a set of drawings  or  plans  to  convey  his  ideas  (or instructions)  effectively  to  a  skilled  craftsman (CE) who is to install the electrical system. It is also  equally  important  for  you,  as  an  EA,  to understand and be thoroughly familiar with the methods and basic functions associated with the different  materials  and  fixtures  used  in  the installation  of  an  electrical  system. This chapter, when used in conjunction with the   previous   chapters   on   wood,   concrete   and masonry, and mechanical systems and plan, will enable   you   to   prepare   construction   drawings (discussed  in  the  next  chapter),  revise  as-built drawings   in   the   field,   and   incorporate   minor design changes with ease. ELECTRICAL  SYSTEM Each building requires an electrical system to provide  power  for  the  lights  and  to  run  various appliances  and  equipment.  At  Navy  bases,  the electrical  (or  power)  system  consists  of  three  main parts: the power plant that supplies the electrical power,  the  electrical  distribution  system  (external) that   carries   the   electrical   current   from   the generating  station  to  the  various  buildings, and  the  interior  electrical  wiring  system  that illuminates  the  building  and  feeds  the  interior electrical power to the appliances and equipment within the building. In  this  section,  we  will  discuss  only  the external  power  distribution  and  the  various materials and fittings used in the installation of an electrical system. For more information, refer to the latest edition of  Construction   Electrician 3 & 2, NAVEDTRA  10636,   National    Electrical Code® (NEC®),  and  Army  Technical  Manuals (TMs). ELECTRICAL  (POWER) DISTRIBUTION SYSTEM Electrical distribution is defined as the delivery of power to building premises, on poles or placed underground, from the power plant or substation through  feeders  and  mains. The power system is generally considered to be  a  combination  of  two  sections:  the  transmission and the distribution. The difference between the two  sections  depends  on  the  function  of  each  at that particular time. At   times,   in   a   small   power   system,   the difference  tends  to  disappear,  and  the  trans- mission   section   merges   with   the   distribution section.  The  delivery  network,  as  a  whole,  is referred  to  as  the  distribution  section  and  is normally used to designate the outside lines and frequently  continues  inside  the  building  to  include power  outlets. Most land-based power systems use alternating current  (ac)  rather  than  direct  current  (dc), principally   because   transformers   can   be   used only  with  ac.  An  ac  distribution  system  usually contains   one   or   more   generators   (technically known  as  ALTERNATORS  in  an  ac  system);  a wiring  system  of  FEEDERS,  which  carry  the generated power to a distribution center; and the DISTRIBUTION CENTER, which distributes the power  to  wiring  systems  called  PRIMARY MAINS  and  SECONDARY  MAINS.  A  repre- sentative transmission and distribution system is shown  in  figure  9-1. Figure 9-1.-Electrical transmission and distribution system. 9-1







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