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BELL SYSTEM TECHNICAL JOURNAL 



matter of judgment and is influenced somewhat by the local con- 

 ditions. In general, it is felt that depths between 16" and 20" 

 are adequate and that more shallow installations are justified only 

 under special conditions. 



The plow equipment that has been developed for this purpose is 

 shown in operation in Fig. 4 and in more detail in Fig. 5. The plow- 

 share is a vertical blade with a tube fastened to the back edge through 



Fig. 5 — -Wire plow in elevated position, showing duct for wires at back of plow-share. 



which one or two pairs of wires may be fed into the soil. The depth 

 of the blade in the ground is readily adjustable to meet local conditions. 

 It has been found that in fairly hard soil with a liberal supply of rock, 

 an equivalent of a 40 or 50 hp caterpillar tractor is required to draw 

 the plow. Across stretches of private right-of-way or at other locations 

 where it is not convenient to use tractors or trucks in direct traction, 

 however, alternative methods have been employed, such as using the 

 winch line of a construction truck to pull the plow. The speed at 

 which the plow may be operated is controlled largely by the number 

 and character of obstacles encountered. Under favorable conditions, 

 the plow may be operated at a speed of three or four miles an hour 

 but a much lower average is to be expected under the less favorable 

 conditions commonly found. 



