TELEPHONE SYSTEM OF THE UNITED STATES 



53 



at intervals of 1,830 meters and at an average interval of about 70 

 kilometers are provided with telephone repeaters which renew the 

 power of the attenuated voice currents. A single standard full size 

 cable 6.7 cm. in diameter when so equipped is capable of providing 

 between 250 and 300 long distance telephone circuits. 



The toll cable system includes various types of construction. For 

 the routes having the most rapid growth, multiple duct subway is 

 used. At the present time with the development of very heavy toll 

 demands in many parts of the country, this type of construction is 



Fig. 43 — ^Typical aerial toll cable construction showing loading point. 



being extended very rapidly on a number of important routes. Mul- 

 tiple tile duct with small splicing manholes located at intervals of 

 229 meters and large manholes for loading coil pots at intervals of 

 1,830 meters are generally used. 



For routes on which the growth is relatively light, for example, 

 40 or 50 circuits a year and where underground construction is de- 

 sirable, two other types of construction have been used to a limited 

 extent. In one type the cable is placed in a single duct of fibre and 

 in the other type of construction cable covered with a double layer of 

 steel tape is placed directly in the earth. With both of these types 

 of construction, manholes are built only at loading points. 



