Shunts cannot be 0 ohms. They usually are a fraction of an ohm. Then the voltage drop across the shunt will determine the amount of current flowing. So on a shunt system, a volt meter is used and is calibrated to the current.
For example: A .01 ohm shunt will have a .01 volt drop across it when 1 amp is being drawn. 30 Amps will be .3 volts, etc. At 30 amps, the shunt will have to dissipate 9 Watts of heat that is wasted in the process.
Having said that, a calibrated piece of wire can function as a shunt. You will need an ohmeter that is capable of measuring fractional values. That is out of the realm of common digital multimeters out there. Just factoring out the test lead resistance in the measurement can be very complicated.
Craig
Determining the resistance of the shunt just requires measuring the current through it and voltage across it at the same time and using Ohm's Law. That's exactly what a regular ohmmeter does but the current is too low for the range of a normal meter and resistance of the shunt. With good instruments it's not that big of a deal.
