We are about to move our hot tub in our garden and need some cable to power it in it's new location, my local electrical factors stock armoured cable that is just the job but they don't know what gauge it should be, the electrician that is going to re wire it is on holiday till Saturday and I need the cable on the job for Monday. The tub is rated at 32 amps and the cable length will be around 25 mts.
You need to work out the volt drop as dresribed in the new IEE BS 7671 17th edition regs.
6mm SWA at 25 metres, which is millivolts per amp per mtr/1000
so 7.3 * 32 * 25/1000 = 5.84 volts which is just in the regulations of 6 volts drop.
Now are you running this cable straight from your main incoming supply or adding onto the cable which is already there as this will make a difference....