It's all in the jargon.

The "Auto" cable has its dimensions measured over the outside of the insulation - it gives no indication of the actual size of the copper within.
I think what Collyn might be trying to emphasise is that for ELV (Extra Low Voltage e.g. 12 volt ) systems the cross-section of the conducting material, usually copper, must be very much greater than that required for normal domestic 240 volt circuitry.
To arrive at the same power transmission, a 12volt wire needs to be 20 times greater in cross-sectional area than for 240 volts.

Remembering that heating within a cable is a function of resistance and current, that thinner wires have greater resistance than thicker ones, and that lower voltage needs more current for the same power needs, you can see that heavier cable is required to both prevent power loss and to reduce the risk of overheated wires setting fire to things.

Here's a link to comparative wire sizing, it helps a bit to cut through the confusion that different standards have created over time.

http://www.powerstream.com/Wire_Size.htm

I hope that this helps.

Rolly

Thanks for clearing that up

Coyotte

240V houshold wire has another problem too. It has much heavier strands and fewer of them. That can lead to snapping of the copper due to fatigue caused by movement and vibration. The use of fine, multistrand able is much more reliable. DO NOT solder joints for the same reason. Use a good quality crimper. Use this formulae (from Collyn) to make sure the cable size is big enough for the current. Voltage drop should be kept well under 0.5V. Any voltage drop is pure loss of power. VOTLAGE DROP = [cable length (in metres) X current (in amps) X 0.0164] divided by cable cross-section in mm.sq. Cheers, Peter