That's why I also wrote "A flat wide copper strip has a smaller impedance than a round conductor with an identical cross section." A 6" wide, 0.003" thick piece of copper strip has a cross section of 22.918 MCM or about the same cross section as a 7AWG wire. A 6" wide .098" thick copper strip has a cross section of 748 MCM, 4/0 cable is 250 MCM. 4" wide by .003" has about the same cross section as 8AWG wire Copper strip comes in numerous gauges in between these two extremes and in widths as wide as 12" (on special order) and smaller. Just as you correctly stated, "the voltage is just a product of high current flowing through an impedance..." any reduction of the impedance reduces the EMF while the current remains the same so a large cross section conductor is needed to handle the current. This can be achieved along with low(er) impedance with a wide, thin (flat) conductor. This is why copper strip is often found in the grounding systems of commercial facilities.