Electromagnetic locating: tracing buried cables and pipes from above

Electromagnetic locating traces a buried cable or pipe by the magnetic field around an alternating current flowing along it. The locator’s receiver finds the peak of that field at the surface, and the service is marked along its run.

OpsChase’s utility locating software records the method used for every service, so the report says how each one was found.

Passive and active signals

Published guidance from the United States Federal Highway Administration describes two kinds of signal:

• Passive: currents already on a line, such as those in live power cables.
• Active: a signal put on the line by the locator’s transmitter, by connecting directly to the line, by induction from the surface, or with a clamp around an accessible section.

Non-metallic pipes carry no signal of their own. They are traced with a tracer wire, or with a sonde, a small transmitter pushed through the pipe and followed from above.

Limits worth reporting

• Plastic, fibreglass or clay pipes without a tracer may not be detected.
• A signal can couple onto a nearby service, especially in a shared trench, and lead to the wrong line being marked.
• A passive locate depends on current, not voltage. A live cable with no load may show no signal and is still dangerous.

Where it sits in quality levels

The Before You Dig Australia (BYDA) Best Practice Guide treats electronically located services as Quality Level B under AS 5488, the Australian Standard for subsurface utility information. Services need exposing to reach Quality Level A. See quality levels.

How OpsChase records it

For each service the locator picks the method, adds depth where known and the quality level, and attaches photos of the paint and pegs. The report sets methods and limitations out the same way on every job.

On OpsChase: one queue for your team and contractors, follow-up when a job goes quiet, and photos or sign-off before it closes. Book a demo — one site or many.