other  existing  utilities,  there  should  be  existing utilities maps that can be used in the design of the new utility  line.  Consequently,  in  cases  such  as  this, reconnaissance and preliminary surveys are seldom necessary. On the other hand, a power transmission line  or  other  utility  running  through  open  country  on a large military installation may require reconnais- sance and preliminary surveys in addition to the final- location  survey. For   discussion   purposes,   let’s   consider   route surveys  for  overhead  electrical  lines. Route Surveys for Overhead Electrical Distribution  and  Transmission  Lines The  reconnaissance  survey  for  electrical  power lines  employs  many  of  the  same  principles  and practices that you studied for highway work; however, the design considerations are different. For a power line, the design engineer considers principles that you studied in chapter 2 of this TRAMAN to select one or more tentative routes over which the line will pass. For convenience, those principles are listed as follows: 1. Select the shortest possible route. 2.  Follow  the  highways  and  roads  as  much  as possible. 3.  Follow  the  farmer’s  property  or  section  lines. 4.  Route  in  the  direction  of  possible  future  loads. 5.  Avoid  going  over  hills,  ridges,  swamps,  and bottom  lands. 6.  Avoid  disrupting  the  environment. During the reconnaissance phase, you should first study all available maps of the area to gain a general understanding of the landscape. If a portion of the line is off the military installation, determine the owner- ship of the lands through which the line will pass. That is necessary to obtain permission to run the line. Look for  any  existing  utilities  that  may  already  exist  in the area. If there are existing utilities, then look for existing  utilities  maps.  Visit  the  area  to  examine  the terrain and look for any natural or man-made features that may hinder or help the construction. In short, gather all information that the engineer will need to select  one  or  more  general  routes  for  the  power  line. With the tentative route or routes selected, you are ready to conduct a preliminary survey from which a map  is  prepared  showing  the  country  over  which  the line will pass. Since the final location is not known, a wide strip of land needs to be mapped. When running the  preliminary  survey,  incorporate  all  pertinent topographic  information  into  the  field  notes.  Note particularly  any  existing  overhead  or  underground lines  and  indicate  whether  they  are  power  or communications lines. Locate such features as hills, ridges,  marshes,  streams,  forests,  roads,  railways, power  plants,  buildings,  and  adjacent  military  camps or bases. When  the  preliminary  mapping  is  completed,  the engineer selects the final route. Again, the engineer considers  the  principles  listed  above  to  select  the route. POLE  LINE  SURVEYS.—  When the route has been selected, a plan and profile are plotted. The plan shows the route the line will follow and the significant topography adjacent to the route. The profile shows the ground elevation along the line and the top eleva- tions  of  the  poles.  These  elevations  are  set  in  accord- ance  with  minimum  allowable  clearances  specified  in the National  Electrical  Safety  Code  (NESC),  ANSI C2,  and  the  most  recent  edition  of  the  National Electrical   Code^® (NEC^®). For distribution lines, poles should be placed on the side of the street that is most free of other lines and trees. Try to keep off the main streets. As much as possible, you should use the same side of the road throughout the length of the line. For straight portions of lines, the usual spacing between poles is about 125 feet  (100  feet  minimum  and  150  feet  maximum); however, to make the poles come in line with property lines  or  fences,  the  span  length  may  need  to  be adjusted.  The  engineer  will  determine  the  spans. Along roads, poles should be placed 2 feet from the inside edge of the curb or 2 feet from the edge of the road  surface  where  curbs  do  not  exist.  On  open roadways or highways, poles should be set 18 inches from the outside of fences. For  transmission  lines,  poles  should  be  located  in high places so that shorter poles can be used and still maintain the proper ground clearance at the middle of the  span.  Avoid  locating  poles  along  the  edge  of embankments  or  streams  where  washouts  can  be expected. In rolling country, the grading of the line should  be  considered  when  determining  pole locations. A well-graded line does not have any abrupt changes up or down the line and will appear nearly horizontal regardless of small changes in ground level. Sometimes, by shifting a pole location a few feet, a standard length pole can be used where otherwise an odd-sized   pole   would   be   needed.   In   addition, transmission line poles should be located at least 2 feet 10-2