LIGHTNING PROTECTION OF BURIED TOLL CABLE 



287 



they may do so (i.e. many of the currents in excess of ii may arc to the 

 cable, although this is not essential in order to produce cable failure). 



1000 



00 



u 



s 



05 

 O 





500 



200 



100 



50 



20 



10 



=1 (2ta/2 

 q V ' 



100 



500 1000 



mi, 



Figure 9 — Solution of the equation: 





'"-"=:ey 



If strokes to ground not arcing to the cable were neglected as a source 

 of failures, the number of failures would equal: 



n,i = INsp'qHii,) (95) 



If, on the other hand, the dielectric strength of the earth were assumed 

 to be infinite, so that none of the strokes to ground would arc to the cable, 

 the number of failures would equal 



INsp^ (^-^ G{i,, 



mk) 



(96) 



