Choosing the correct locating tool is the first step in significantly decreasing the risk of utility damage and personal injury on-site. Whether you are searching for a buried power cable, a plastic water pipe, or a lost manhole cover, using the right technology is critical.
This guide breaks down the three primary types of underground locators: Magnetic Locators, Electromagnetic (Pipe & Cable) Locators, and Ground Penetrating Radar (GPR).
Quick Selection Chart
Use this table to identify which technology suits your specific needs:
| Need to Find? | Magnetic (MAG) | Electromagnetic (EML) | Ground Radar (GPR) |
| Iron or Steel Pipes | Yes | Yes | Yes |
| Copper Pipes | No | Yes | Yes |
| Live Electrical Cables | No | Yes | Yes |
| Telecommunication Wires | No | Yes | Yes |
| Non-Metallic / Plastic Pipes | No | With Sonde | Yes |
| Manhole Covers / Steel Lids | Yes | No | Yes |
| Survey Pins / Nails | Yes | No | No |
| Septic Tanks (Rebar) | Yes | No | Yes |
1. Magnetic Locators (MAG)
Magnetic locators sense and react to ferrous metals (iron or steel) only. They do not detect copper, aluminum, or plastic.
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Best For: Finding survey pins, nails, manhole covers, valve boxes, and reinforced septic tanks.
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Depth: Can locate small items like nails at depths of up to 5.48m (depending on soil conditions).
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How it works: It detects the magnetic field of the earth as it is distorted by a ferrous object.
- See: Schonstedt Locators
2. Electromagnetic Locators (EML)
This is the most common type of locator used by utility contractors. It consists of two main parts: a Transmitter (to apply a signal) and a Receiver (to pick up the signal).
- See Radiodetection Locators
Key Features:
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Active Locating: You connect the transmitter to a pipe or cable to "energize" it with a specific frequency.
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Passive Locating: The receiver can detect "natural" signals, such as the 50Hz hum of live power cables, without using the transmitter.
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Sondes: To locate plastic pipes, a battery-powered "Sonde" (mini transmitter) is pushed through the pipe using a rodder. The receiver then tracks the Sonde from above.
Essential Accessories:
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Signal Clamps: Allows you to apply a signal to a cable safely without interrupting the service.
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A-Frames: Used specifically for finding sheath faults (breaks) in buried cables.
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Trace Rodders: Flexible rods with internal wires used to trace the path of non-metallic conduits.
3. Ground Penetrating Radar (GPR)
GPR is the most versatile tool because it can "see" both metallic and non-metallic objects.
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Best For: Locating plastic (PVC) pipes, concrete pipes, and underground storage tanks where no tracer wire is present.
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Visual Interface: Provides a real-time "map" or cross-section of what is beneath the ground on a digital screen.
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Limitation: Performance is highly dependent on soil type. It works best in sandy, dry soils and struggles in heavy clay or highly conductive wet soils.
- See Sensors & Software Detectors
Understanding Frequencies
Choosing the right frequency is vital for Electromagnetic Locators:
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8kHz & 33kHz: The "standard" frequencies that cover most general locating tasks.
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131kHz: Ideal for the telecommunications industry to induce signals on small copper pairs.
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Low Frequencies (512Hz / 640Hz): Typically used for deep-target locating or with specific Sondes.
Conclusion
Selecting the right locator depends entirely on what you are trying to find and the ground conditions you are working in. For most utility work, an Electromagnetic Locator is the gold standard, but for "blind" locates where no connection is possible, GPR is your best ally.
Need Expert Advice?
If you're still unsure which locator fits your project, contact our technical team for a consultation.