CHAPTER 11. 



PRINCIPLES OF DESIGN AND CONSTRUCTION OF 

 CABLES. 



The specification for a new cable generally exacts a guarantee 

 for the attainment of a certain speed of signalling. If the 

 cable is to be laid between shores already connected by other 

 cables, a higher rate of signalling than on any of the existing 

 cables is generally required. In order to calculate the weights 

 of conductor and insulator, to ensure the required speed being 

 attained when the cable is laid, information from the most 

 trustworthy sources as to the depths and temperatures of the 

 ocean along the proposed route must be at hand. If no cable 

 has been laid there before, the charts are referred to for depths. 

 The charts, however, do not give the data on bottom tempera- 

 tures, nor sufficient data on depths, and a margin has therefore- 

 to be allowed in the calculations. Where cables have been 

 laid the mean temperature of sea bottom can be accurately 

 calculated from measurements of the conductor resistance, and 

 the depths are fairly well known and checked during subsequent 

 repairs. A great deal of information of this kind has thus 

 become known which would not otherwise have been brought 

 to light. 



Principles of Design. — An important factor to consider in 

 design is what is termed the KR of the cable. This is the total 

 capacity of the cable in microfarads (K) multiplied by the total 

 resistance of the conductor in ohms (R). The total capacity of the 

 dielectric is the capacity per naut in microfarads (k) multiplied by 



