Hi Bob
That is an interesting table. I was using the figures normally quoted for thinwall cable which appear to be very similar to the column labelled "85 to 90c" from the table.
So I agree, a 10mm2 cable is the one to go for (I am rewiring my Plus 2, adding relays and fuses etc. and this is what I am doing). As to the fuse, I am putting one midi fuse straight after the power lead comes from the solenoid. The information I have is that these fuses don't quite work as we all imagine. Take a look at this page:
http://www.littelfuse.com/data/en/Data_Sheets/498.pdfSo a 50amp fuse will last for at least 100 hours at a continuous 50 amps (and that is quite a long journey!!). But to blow within a guarranteed 15 secs it needs to be handling 150amps! Even at 75amps it would last a minimum of 90 secs. So I have been conservative and gone for a 50amp fuse rather than a 70amp one on the basis that I want to protect my wiring.
I have worked out that it is theoretically possible to draw 70-80 amps from the battery but you would need everything to be on continuously (lights, ignition, indicators, heated rear screen, reversing lights, stop lights, heater fan, wipers etc.) and not have got roung to starting the engine (and thus get some current from the alternator). In that situation the 50amp fuse would blow in 90 secs - and it would have been my fault for being stupid.
I suppose the other comforting thing is that if there is a catastrophic short circuit through the alternator, or a chafed wire, the current is likely to go very very high and thus blow any fuse pretty quickly.
Finally, all the above is a good reason not to get an 80amp alternator - you will need to put in even thicker wire to cater for the event that the alternator tries to charge a flat battery. Stick to the 45amp variety.
Richard