A shunt is a low-ohm resistor that can be used to measure current. Shunts are always employed when the measured current exceeds the range of the measuring device. The shunt is then connected in parallel to the measuring device. The entire current flows through the shunt and generates a voltage drop, which is then is measured. Using Ohm's law and the known resistance, this measurement can then be used to calculate the current (I = V/R). To keep power loss - and thus heat generation - to a minimum, shunts must have a very low resistance value measurable in milliohms.

Shunts are basically suitable for any type of current measurement - be it with a direct or alternating current.