Shower Cable - to be 6mm2?

whats the maximum lenght for a radial circuit in 2.5 on a

20amp mcb
16amp mcb

where can i find this out ?

 

whats the maximum lenght for a radial circuit in 2.5
on a

20amp mcb
16amp mcb

where can i find this out ?


30metres for 20A, (TN supplied)

pro rata for 16A..?

 

What are the odds that the shower maker is quoting the rating of his product at 240V, and that if you want to do the 230V calculation you should use the lower number that you might find in the small print, or which you might need to calculate as 9500x230²/240²....?