What is a shunt?

Just had a great customer call in and ask a seemingly easy question: What is a shunt? Well, 3 office people later, I had to call in the NACE C. P. Specialist big gun to answer the question.

A shunt is a precision resistor that allows you to measure the amperage or current in a circuit by measuring the voltage drop across the shunt. A shunt is important because you can measure the current without breaking the circuit. Breaking the circuit is generally frowned upon (it's what protects the metal substructure!), and can be time consuming: instead of clipping your multimeter's alligator clamps onto the shunt, you need to remove the test leads from each of the terminals, connect them to the meter, then remove them from the meter and put them back on the test station. Repeat that 20x a day and tell me if it isn't worth a $5-$9 little instrument?

Ideally when selecting a shunt, you would choose one with the least amount of resistance; particularly for sacrificial systems you would want to choose a 0.01-ohm or 0.001-ohm resistance shunt. An impressed current system can handle the resistance better and a 0.1-ohm resistance shunt may be appropriate.