The art of locating is based upon detecting electrical current on a target conductor, usually a pipe or cable, underground. A transmitter is used to apply this current to the target line and a receiver is used above ground to detect the electrical fields generated by this current. In almost all cases, more current flowing through the target conductor, will provide a stronger signal that is easier to locate accurately.

Electrical current can only flow if a circuit is present. A locating circuit is a closed loop between a transmitter and a conductor. The loop is created when current flows from the transmitter, through the conductor (utility), and then back to the transmitter. The better the circuit (less resistance) the more efficiently the current can flow, and the stronger the locatable signal. In this article we will explore what makes a good locating circuit.