Quantcast Cable Placement

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TABLE 3-3
EXPECTED SOIL RESISTIVITIES






Resistivity

  


 OHM-Centimeters


OHM-Meters

  


 Soil Types
Minimum  Maximum
 Minimum
 Maximum


  
  
 Clay, Moist
 1,400    3,000



14
30
 Swampy Ground
 1,000    10,000

  100

10
 Humus and Loam
 3,000    5,000



30
50
 Sand Below Ground-Water Level
 6,000    13,000

  130

60
 Sandstone
 12,000   7,000,000

 70,000

120
 Dry Sand
 20,000   7,000,000

 70,000

200
 Broken Stone Mixed with Loam
 20,000   35,000

  350

200
 20,000   400,000

 4,000

200
 Dry Earth
 100,000  400,000

 4,000

1,000
 Dense Rock

 1,000,000

 10,000

 Crushed Rock
 300,000  400,000
 3,000
 4,000


  

(e) Oil circuit breakers require two grounds.
(f) Station fences require complete perimeter ground cables, located three feet outside
the fences, and are connected to the station grid. Ground spacing should not exceed 75 feet.
Fences require a fabric ground for approximately every 75 feet and a post ground for every third
post.
(g) All station gates require connection to both gate posts and copper braid to connect
the hinge posts to the gate.
3.8.1.4 Measurement of Soil Resistivity. An earth resistivity measurement of the soil is
important and should be carried out upon installation of the ground grid to assure accuracy of the
grid placement and to assure no loose ends or bad connections exist. The most common method
used to measure the soil resistivity is the four pin method.
3.8.2 Cable Placement. After the above ground connections are completed, the underground
cable, connecting cable, and ground rods should be placed. Cables should be laid in parallel lines
with reasonable spacing to connect these points. Ground rods should be placed at crossings and
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