220 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



CABLE 



Choice of Design 



Since 1930, when the Key West-Havana No. 4 cable was constructed,^ 

 it has been usual to extrude the insulation of coaxial submarine cables 

 to a diameter of about 0.62 inch, and most of the cables in the waters 

 around the British Isles are of this size. The experience of the British 

 Post Office with submerged repeaters'^ in its home ^vaters, dating from 

 1944, when the first repeater was laid between Anglesey and the Isle 

 of Man,* has therefore been mainly with 0.62 inch cables, first with para- 

 gutta as a dielectric and later with polyethjdene. Most of these cables 

 were originally operated without repeaters, and the 60-circuit both-way 

 repeaters which are now installed on the routes were designed to match 

 their characteristics. 



In planning a new system, the size of cable will be determined by one 

 of the following considerations: 



(i) Minimum annual charges for the desired number of circuits. 

 (ii) Terminal voltage required to feed the requisite number of re- 

 peaters. 



(iii) Maximum number of repeaters or minimum repeater spacing 

 which is considered permissible. 



(iv) Maximum (or minimum) size of cable which can be safely handled 

 by the laying gear in the cable ship. 



Fig. 3 • — Cross-section of cable across Newfoundland showing make-up. A. 

 Centre conductor, 0.1318-inch in diameter copper. B. Three 0.0145-inch copper 

 surround tapes. C. Polyethylene to 0.620-inch diameter. D. Six 0.016-inch copper 

 return tapes. E. 0.003-inch overlapped copper teredo tape. F. Impregnated cotton 

 tape. G. Five iron screen tapes. H. Impregnated cotton tape overlapped. J. Poly- 

 ethylene sheath to 1.02-inch diameter. K. Inner serving of tanned jute yarn. L. 

 Armour wire 29 x 0.128-inch diameter. M. Outer serving of tarred jute yarn. 



