The first thing you need to do is what pete01 wrote in the first reply - though I would turn each one on individually. Then you'll know which circuit has the problem.
Let us know the result and we can give further help.
You need a table that applies to the cable you use. It doesn't matter what the heading of the table is. 4E2 applies to H6242B - the manufacturer's data sheet says so.
https://www.tlc-direct.co.uk/Products/CACAT6EXTslash1.html
You need to make sure it is appropriately secured so that is doesn't move about and chafe in the wind etc.
You can get armoured versions both in CAT5E and CAT6:
https://www.tlc-direct.co.uk/Products/CACAT5EslashSWAslash1.html
For the...
Taking hand to hand resistance as typically 1000Ω, using your example above the touch voltage at the fault would be 52.5V and the current across the body 52mA - so very likely fatal, less likely but not impossibly so if RCD protected due to the route of the current through the body.
Ah, to me your post was suggesting that the regs required a neutral at the switch and that he would know that if he had read them.
The wonders of English, eh?
All the regs say is "Consideration shall be given to the provision of a neutral conductor, at each switch position ". He's considering it, hence his question!
My guess is that the electrician is proposing to add an extra (32A) MCB (not RCD or RCCB) to the existing RCD protected CU, which would indeed be about a tenner.
Satnavs use a modified version of Dikstra's Shortest Path First algorithm, which is the foundation of the OSPF routing algorithm used by Autonomous Systems in the Internet.
This is not really surprising, as the road system is a network too.