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BELL SYSTEM TECHNICAL JOURNAL 



and underground connections to aerial plant require vertically run 

 wires on jointly used poles. The location, insulation and mechanical 

 protection of these have received special consideration to eliminate 

 hazards to workmen. 



Sufficient clearances between vertically run circuits of one type and 

 the equipment of another utility on jointly used poles have also been 



a a 



Communication 

 Cable Terminal 



Fig. 1 — Typical jointly used pole. 



found to be very important from the standpoint of avoiding interrup- 

 tion to power and telephone services. 



In the course of electrical storms, lightning may induce high voltages 

 on either supply or communication wires. If the separation between 

 the supply and communication facilities is not adequate at any point, 

 these induced voltages may break down the insulation and arc between 

 the two as illustrated in Fig. 2. Damaged plant may, of course, result 

 from lightning alone. However, when lightning has established an arc 

 between the power and communication circuits the normal voltage of 



