COOPERATIVE WORK OX JOINT USE OF POLES 235 



the supply circuit may maintain the arc. This results in the transfer 

 of power into the telephone plant at voltages which may be well above 

 that for which it is insulated and may cause trouble on both the power 

 and telephone system. This sort of abnormal belongs to the general 

 class that includes insulator flashovers, short circuits on cables, tree 

 grounds and similar power system occurrences that always carry the 

 probability of damage to the power system or service. 



While vertically run attachments with improper clearances have 

 played a large part in causing such occurrences, any situation where 



fc-* 



Fig. 2 — Frayed insulation showint^ breakdown of insulation between power and 



telephone plant.* 



insufftcient clearance between power and telephone facilities is pro- 

 vided may result in similar trouble. 



Emphasis has, therefore, been placed in present day standards on the 

 necessity of maintaining proper clearances as well as strength of con- 

 struction to prevent this kind of abnormal. Experience has shown that 

 where these clearances are adhered to this type of abnormal is kept to a 

 reasonable minimum. 



The Joint General Committee is giving careful consideration to the 



matter of construction standards on jointly used poles. Pending the 



development of complete specifications covering recommended prac- 



* In order to obtain a satisfactory photograph of the points of arc the vertical 

 drop has been straightened out so that the clearance shown is much greater than 

 existed at the time of the arc. 



