Most underground power line locators work on the principle of electromagnetism. The system typically consists of two main parts: a transmitter and a receiver.

• Passive Locating: The receiver unit detects a naturally occurring electromagnetic field that radiates from an energized (live) power line. This method is fast but may not provide high precision and only works for lines carrying a current.

• Active Locating: This method is the most precise. The transmitter applies a specific, traceable electromagnetic signal onto the target line. This can be done by physically connecting a lead to an access point (like a ground stake) or by inducing the signal from above the ground. The handheld receiver is then tuned to this specific frequency and can accurately trace the exact path and even estimate the depth of the buried cable.

Some advanced locators also use Ground-Penetrating Radar (GPR), which sends radio waves into the ground and creates a subsurface image based on the reflections. GPR is particularly useful for locating non-metallic utilities, but electromagnetic locators remain the primary tool for power lines.