Ammeter Shunt -150/150AMP - 60mV Input - 12/24VA shunt is a resistor that causes a small voltage drop. This voltage drop in mVolt is proportional with the current in ampere that goes through the resistor. This voltage is measured by the Ammeter. The advantage of the shunt is that thick wires are no longer needed at a high current (>10 A). To measure the total flow you only need two thin wires from the measuring instrument to the shunt in the earth connection of the main system.