Joe T. wrote:They make plastic coated copper tubing for underground use.
Is the plastic rated for high enough voltage insulation factor for the voltage your system will run at? If it's not marked as rated for a voltage, you'd have to find out what kind of plastic it is, then what thickness, then look up what voltage that would insulate against. (or just take it as it is and hope it's enough).
Also note that some plastics have very low melting or distortion points, so that if the wiring gets warm or hot in use, the insulation could come off. The stuff used on some 18650 cells and on electrolytic capacitors is one example of that--I've seen a number of those that have heated up and split their plastics, and the 18650s have caused pack failures from shorting cells (or cells to tabs) together when that happens.
I am assuming the price for 1/2" tubing is cheaper than 1/2" stranded wire.
I don't know about the price, but 1/2" tubing won't have nearly the same copper crosssection (and thus current-carrying ability) as 1/2" wire. You have to use tubing with the same copper crosssection as the wire you'd otherwise have used. That's going to be a lot larger diameter than the wire would be, depending on wall thickness.
I seem to remember from school, many decades ago, current traveling on the surface of the conductor.
At very high frequency AC, yes (like RF). With motor control, it's still effectively all DC as far as that goes.
I have not researched it much since. I figured I would comment here and get a head start. You mention cross section. Obviously tubing is hollow but would have the same diameter and thus, surface area.
It does not have the same crosssection, meaning it does not have the same amount of conductive material, so it can't carry nearly as much current as a wire (solid or stranded) of the same diameter.
So the pipe will have to be more than twice the diameter of the wire, depending on wall thickness. (thinner wall = larger diameter required).
I figured some one here would have explored this long ago.
It's probably been tried for watercooling motors, using the tubes to carry the cooling fluid in as well as the power, but I don't know what thread it would be in. You'd probably have to search on the word "pipe" or "tube" along with maybe "copper" and "motor" to find them, and then see what comes up and sort thru it. :/
But I don't see any advantage (and more than one disadvantage) to the tubing over the wire, other than stiffness (which is usually also a disadvantage in a moving vibrating vehicle).