I have asked the question to some engineers and researched on the internet no one can tell me for sure why in a surge protection device (like the type we use in our switchgear) the supply fuse is rated at 63A but we use 35mm cable this seems a bit much. I was told this is because a large surge will create a back EMF in the center of the cable causing the current to flow round the outside. could someone shed some light on this subject PLEASE

 

High energy transients can be modeled as high frequency electromagnetic phenomena. At high frequency the cable impedance could be significative if it is not properly designed. Cable could be big for DC current flow but its design was made considering the complete transient electro magnetic phenomena.