Thanks for the advice Andy, very useful. No, I'm not a part time electrician and although not scared of tackling most DIY stuff, you may have said enough to make me re-think this one!
Very new to electric bikes/conversions but am thinking of buying a used motor hub and having a wheel builder fit it to a 20" rim for a folding bike conversion. The issue I'm a bit uncertain over is whether hub motors are built specifically for particular wheel sizes? Apparently this particular motor was originally used on a 29" MTB wheel so does it follow that it can just as easily be used on a 20" rim? Or is that ignorant thinking?!