CAT and Genny Not Pick Up

← Part of the Series: The 2026 Ultimate Guide to Cable Avoidance (CAT & Genny)

What Can a CAT & Genny NOT Detect? (The Invisible Dangers)

The Radiodetection C.A.T4 is a marvel of engineering, but it is not magic. It operates on the laws of physics—specifically electromagnetism. If a buried asset cannot conduct electricity, or if it doesn't have a tracer wire, a standard CAT and Genny will not find it.

Believing your locator finds "everything" is the fastest way to a utility strike. In this guide, we expose the invisible dangers—the limitations of electromagnetic location—and how to overcome them using 2026 best practices.

Table of Contents

The Core Rule: Conductivity

A C.A.T (Cable Avoidance Tool) is essentially a radio receiver. It listens for a signal running along a line. Therefore, for a line to be detected, it must be metallic (conductive). Anything that insulates electricity is invisible to the standard modes (Power, Radio, Genny).

The Plastic Problem (Water & Gas)

Since the 1990s, the UK utility industry has aggressively switched to MDPE (Blue/Yellow Plastic) and PVC pipes for water and gas mains. They are durable, cheap, and completely invisible to a C.A.T4.

The Danger: You scan a footpath. You get no signal. You assume it's clear. You dig, and you hit a high-pressure 125mm gas main. The plastic pipe didn't carry a power hum, didn't re-radiate radio waves, and couldn't carry your Genny signal.

Clay, Concrete & Fibre Optics

Plastic isn't the only enemy.

  • Clay Pipes (Victorian Sewers): Verify common in London and older UK cities. Invisible to EMF.
  • Concrete Culverts: Large storm drains often have no metallic reinforcement that is continuous enough to trace.
  • Fibre Optic Cables: While the data travels as light (undetectable), most fibre cables have a metallic "armoured" sheath or a copper tracer wire. However, if this sheath is broken or not earthed, the fibre line becomes effectively invisible.

Signal Masking & Distortion

Even when cables are metallic, they can hide.

The "Big Signal" Masking Effect

Imagine trying to hear a whisper at a rock concert. If you have a massive high-voltage (HV) cable radiating a screaming 50Hz signal, it can "drown out" the tiny signal from a nearby telecoms cable. The CAT will lock onto the big signal, and you might assume that's the only thing there. Solution: Always scan in Genny Mode using a high frequency (like Small Diameter Locate) to try and pick out the smaller lines from the background noise.

Pot-Ended Cables

A "Pot-Ended" cable is a live cable that has been cut and capped (e.g., for a future house build). Because no current is flowing through it to a house, it generates no magnetic field. It is live, deadly, but silent in Power Mode. Only a Genny signal (Induction) stands a chance of lighting it up.

How to Find the "Unfindables"

So, how do we find plastic and clay? We have to introduce something metallic into them.

  1. FlexiTrace: This is a 50m-80m fibreglass rod with copper conductors. You push it up the plastic pipe. You connect your Genny to the rod. The entire rod lights up, and you trace the rod from above ground.
  2. Sonde (The Mouse): A small battery-powered transmitter. Screw it to a drain rod, push it up the sewer. The C.A.T4 tracks the "beep beep" of the mouse deep underground.
  3. Ground Penetrating Radar (GPR): For when access isn't possible. GPR (like the LMX100) sends radar pulses into the soil. It detects the density change between the soil and the pipe. It can see plastic, concrete, and even voids.

Conclusion

Never rely on a "Silence is Safe" mentality. If your plans show a water main but your CAT is silent, it is almost certainly plastic. You must switch tactics—use a Sonde, GPR, or trial holes. Knowing the limitations of your kit is the hallmark of a true professional.

Recommended Gear

  • CAT4 - View Professional Range
  • Genny - View Professional Range
  • Sonde - View Professional Range
  • Flexitrace - View Professional Range

Why Professional Equipment Matters

In the field of utility surveying and safety, "cheap" equipment is arguably the most expensive mistake you can make. False readings leading to a cable strike, or a failed gas monitor in a sewer, can cost lives and millions in liability.

At Cable Locators & Survey, we stock only the verified industry standards—Radiodetection, C.Scope, Abtech, and Leica. Every unit is checked, calibrated, and field-ready.