COOPERATIVE WORK ON JOINT USE OF POLES 233 



which have been recommended iind are the basis upon which practically 

 all cooperative work is being carried forward. 



It is the purpose of the following paragraphs to describe what has 

 been done and what is being done by the Joint Subcommittee on De- 

 velopment and Research in connection with the engineering and econ- 

 omic problems which have been encountered in joint use work. 



Construction Practises 



Joint use construction practises have undergone almost continual 

 change and improvement from the time joint use was first adopted and 

 continued development is to be expected in the future. However, 

 many of the fundamental requirements for securing satisfactory con- 

 ditions on jointly used poles were recognized at an early date and form 

 the basis for present day practise. 



In the matter of relative levels it has been recognized that power 

 wires should as far as practicable be carried in the upper position. In 

 general, they are larger and stronger than the telephone wires. This 

 is inherently so because of the current carrying capacity required. 

 Placing power wires in the upper position on jointly used poles avoids 

 the necessity of telephone linemen climbing through power circuits, the 

 exact nature and characteristics of which they are not always familiar 

 with. 



Clearances must be provided which give sufficient space below the 

 power wires so that power linemen will not have to come in contact 

 with telephone wires while they are working on power wires. This 

 neutral space must also provide sufficient clearances above the tele- 

 phone equipment so that telephone linemen may work on the telephone 

 plant without danger of coming in contact with power equipment. 

 Clear climbing space must also be provided so that linemen may climb 

 poles without having to be extremely careful to avoid falls or contacts 

 with circuits from which they may receive physical injuries. 



Fig. 1 shows one method for securing satisfactory conditions on a 

 jointly used pole carrying circuits which both the power and telephone 

 groups have recognized as being suitable for joint use. 



In the matter of mechanical strength, joint use follows the practise 

 in the construction of separate lines. That is, strength of construction 

 should be provided such as to stand, with reasonable factors of safety, 

 storm conditions which experience indicates are likely to occur from 

 time to time in any particular area. 



With regard to the matter of insulation and electrical strength, prac- 

 tises as to the size and type of power insulators hiive followed develop- 

 ments in the general field of power construction. Wires to street lights 



