ANSWER

If you would care to read the electrical notes on www.TB-Training.co.uk you will find both a description of the calculation you need to do. Although I could tell you the cable size required for 12 amps (6 x 2) you need to
concern yourself with voltdrop, so a calculation is required.

Please remember that you should use multi-strand cables with at least 16 strands for new RCD compliant work.

2mm sq, 28/030 cable will be fine in short lengths (say up to 2 or 3 metres) otherwise do the calculations to ensure you do not build in spurious "flat battery" symptoms because of voltdrop on long cable runs.

Using over size cables is only detrimental to your chequebook, electrically its fine.

Tony Brooks