2026 Cable Avoidance Guide: CAT & Genny & HSG47 Compliance
The 2026 Ultimate Guide to Cable Avoidance (CAT & Genny)

The 2026 Ultimate Guide to Cable Avoidance (CAT & Genny)

• 11 min read • 2 views

The Vital Importance of Cable Avoidance in 2026

In the high-stakes environment of UK construction and utilities, the adage "safe by accident" simply does not exist. Utility strikes hitting an underground cable or pipe remain one of the most persistent and lethal risks in the industry. As we progress through 2026, the complexity of our underground infrastructure is growing exponentially, with fibre optics, high-voltage renewables connections, and district heating pipes crowding already congested easements. For Site Managers, Surveyors, and Civil Engineers, the reliance on accurate Cable Avoidance Tools (CAT) and Signal Generators (Genny) is not merely a box-ticking exercise; it is the cornerstone of site safety and legal compliance under the Health and Safety Executive's HSG47 guidance.

This authoritative guide serves as your complete handbook for 2026. We move beyond basic button-pushing to explore the physics of detection, the nuances of the Radiodetection C.A.T4 series, and the professional methodologies that separate a safe site from a disaster zone. Whether you are calibrating a fleet of gC.A.T4+ locators or training an apprentice on their first sweep, this guide provides the definitive standard.

Table of Contents

HSG47: The Legal Framework for Safe Digging

The Health and Safety Executive (HSE) publication HSG47: Avoiding Danger from Underground Services is the primary guidance document in the UK. Failure to adhere to its principles is not just poor practice; in the event of an accident, it can be cited as evidence of negligence under the Health and Safety at Work etc. Act 1974.

The Three Pillars of HSG47

HSG47 outlines a robust workflow that must be followed for every excavation, no matter how minor:

  1. Planning the Work: This involves obtaining current utility plans ("stats") from asset owners (DNOs, Water Boards, Telecoms). In the context of PAS 128, this constitutes a "Level D" survey. These maps provide an indication of what is present, but they are never 100% accurate. Cables differ from plans, depth is rarely recorded, and "dead" cables may still be live.
  2. Locating and Identifying: This is where the CAT and Genny come into play. It involves actively sweeping the ground to confirm the presence of mapped utilities and, crucially, to identify unmapped services. This corresponds to PAS 128 Level B (Detection).
  3. Safe Excavation: Once lines are marked, excavation must proceed with extreme caution. This typically means hand-digging or using air-vacuum excavation within 500mm of the indicated line. Mechanical excavators (JCBs) should never be used directly over a marked utility.

The Science of Detection: How CATs Actually Work

To use a locator effectively, one must understand what it is detecting. A C.A.T does not "smell" copper or plastic; it detects Electromagnetic Fields (EMF).

Passive vs. Active Signals

Passive Signals are naturally occurring fields that exist on a cable without you doing anything.

  • Power Signals (50Hz): Created by current flowing through a live power cable. Crucial Note: A live cable with no current flowing (e.g., a street light during the day) emits no power signal. It is "live" but invisible to Power Mode.
  • Radio Signals (VLF): Very Low Frequency radio waves from distant transmitters permeate the ground. Long metallic conductors (like pipes or telecom cables) act as antennas, re-radiating these signals.

Active Signals are artificially created fields that you, the surveyor, apply using the Genny.

  • Induction: The Genny broadcasts a signal into the ground, which induces a current onto any nearby conductors.
  • Direct Connection: A physical metal-to-metal connection injects the signal directly into the specific pipe or cable. This is the "Gold Standard" of locating.

Hardware Deep Dive: The Radiodetection Ecosystem

Radiodetection remains the market leader in the UK, and their C.A.T4 (Cable Avoidance Tool Gen 4) is the site standard. However, the range is split into specific models, each serving a different purpose.

1. C.A.T4 (Standard Model)

The baseline safety tool. It features the classic Power, Radio, and Genny modes, plus "Avoidance Mode" (A) which scans all three simultaneously. It includes "StrikeAlert," a shallow cable warning system that alerts the user to shallow power cables (typically <300mm depth).

2. C.A.T4+ (Depth Estimation)

The "Plus" denotes the addition of Depth Estimation. When used with a Genny4 in Genny mode, holding the button down provides a depth reading. Note: Depth is only accurate on a clean, solitary signal (Active Mode). Never trust depth readings on passive power signals due to distortion.

3. gC.A.T4+ (GPS & Data Logging)

The "g" stands for GPS/GNSS. This model records every trigger pull, mode change, and swing speed, geotagging the data. This allows managers to review usage patterns remotely, ensuring teams are actually scanning rather than just walking about.

The Genny4 Difference

The Genny4 is a significant upgrade over previous signal generators. Its key innovation is the Dual-Frequency Output.

  • 33kHz Signal: The standard utility frequency, excellent for general induction.
  • Small Diameter Locate Frequency: A secondary high-frequency signal is simultaneously transmitted to "jump" onto smaller, non-continuous cables like telecom pairs or street lighting feeds, which 33kHz often misses.

Essential Accessories: Clamps, Sondes & Flexitrace

A CAT and Genny alone cannot find everything. Accessories are required for non-conductive or complex utilities.

Signal Clamps

A Signal Clamp allows you to apply a Genny signal to a live cable (up to 100mm diameter) without shutting off power. By clamping around the sheath, you induce a signal safely. This is essential for tracing specific cables in a crowded trench or substation.

Sondes (The "Mouse")

Sondes are self-contained battery-powered transmitters. They are screwed onto the end of a drain rod (Cobra) and pushed up a non-metallic pipe (like a plastic sewer or clay drain). The C.A.T4 acts as the receiver, tracking the Sonde's progress to map the pipe's route and depth.

Flexitrace

A Flexitrace is a continuous fibreglass rod with copper conductors inside. The entire rod can be energized by the Genny. This is used to trace the entire path of a plastic pipe, effectively turning a non-conductive utility into a detectable one.

The Perfect Survey: A Professional Standard Operating Procedure

To achieve a "Quality Level B" survey result, discipline is key. Follow this proven workflow:

Phase 1: The Passive Sweep

Before unpacking the Genny, walk the site in Avoidance Mode. This gives you a "mental map" of the easy targets main power, shallow feeds, and energized lines. Mark these with paint (Red for Power, White for Telecoms/General). Do not record depth yet.

Phase 2: The Inductive Search

Place the Genny4 flat on the ground, aligned with the expected direction of services. Turn it on to full power. Sweep the area in a grid pattern at least 10 metres away from the Genny (to avoid air-coupling). Mark any new lines that appear. Move the Genny every 20 metres to ensure coverage.

Phase 3: Direct Connection (Precision Tracing)

Identify access points: stop taps, valve covers, lamp posts, or cabinets.

  1. Connect the Red Lead to the metal utility (ensure a good metal-to-metal contact).
  2. Connect the Black Lead to an independent earth stake pushed into the soil 2-3 metres away at a 90-degree angle.
  3. Select Genny Mode on the C.A.T4.
  4. Trace the signal. This is where you measure depth. The signal will be clean, strong, and confirm the exact route.

Phase 4: The 360-Degree Sweep

Finally, perform a sweep at the proposed excavation point. Rotate the CAT 360 degrees on the spot. This checks for cables running "across" your path that you might have missed if you only walked in one direction.

UK Utility Colour Codes (NJUG)

When marking out services, it is critical to use the standardized NJUG (National Joint Utilities Group) colour codes to prevent confusion.

Utility Type Colour
Electricity (HV & LV) Red
Water Blue
Gas Yellow
Telecommunications (Fibre/Copper) Green or White
Sewer/Drainage Black

Always mark the depth (if known) and the date of the survey alongside the line.

Phase 3: Safe Excavation Techniques

Even with the best survey, you must dig safely. The "Safe Digging Zone" is defined as 500mm either side of the marked line.

Vacuum Excavation vs. Hand Digging

Hand Digging: Traditional and reliable, but risky if the spade is sharp. Use insulated tools and dig alongside the line (creating a pilot trench) rather than directly on top of it. Never use a pickaxe.

Vacuum Excavation: The modern gold standard. A "Suction Excavator" uses high-velocity air and a flexible hose to suck the soil away from the pipe without damaging it. This eliminates the risk of a strike almost entirely and is increasingly required by Tier 1 contractors.

Data Logging & GPS: Managing Fleet Compliance

In 2026, data is as important as the dig. The gC.A.T4+ connects to the C.A.T Manager mobile app. This ecosystem solves a major industry problem: falsified surveys.

Common bad habits include "swings" (swinging the CAT like a metal detector instead of keeping it vertical) and "racing" (walking too fast). The data log captures this. A Fleet Manager can pull a report showing:

  • Swing Analysis: Was the unit kept vertical?
  • Mode Usage: Did they only use Power mode and ignore the Genny?
  • Time on Site: Did a 1-acre survey take 5 minutes (impossible) or 45 minutes (realistic)?

Using this data for training (not just punishment) raises standards across the team.

Field Troubleshooting: Ghost Signals & Distortion

Field Distortion: If the electromagnetic field spreads onto nearby fences or other pipes, the signal becomes "confused." If your depth reading fluctuates wildly (e.g., 0.5m to 1.5m in a single step), trust the horizontal position but discard the depth reading. The field is distorted.

Ghost Signals: Sometimes a signal appears to "move" when you raise the CAT. This often happens near chain-link fences which act as massive inductors. To test, lift the CAT 30cm off the ground. If the signal remains strong and steady, it's likely a true utility. If it vanishes instantly, it may be a ground reflection or surface clutter.

Frequently Asked Questions

Can a C.A.T4 detect plastic water pipes?

No. A standard C.A.T4 simply cannot detect plastic (MDPE/HDPE). Plastic is an insulator and does not carry an electromagnetic charge. To find plastic water pipes, you must use a Transsonde (if access allows), a Flexitrace, or Ground Penetrating Radar (GPR).

What does the "StrikeAlert" warning mean?

StrikeAlert detects a shallow, high-current power cable. If the alarm sounds (a distinctive warble) and the display flashes, you are likely standing directly over a power cable less than 300mm deep. Stop digging immediately and re-verify the depth using safe trial holes.

What is the difference between Power and Radio mode?

Power mode listens for 50Hz mains electricity. Radio mode listens for VLF radio signals. You need both because some cables (like telecoms or balanced HV lines) do not emit a 50Hz hum but will re-radiate radio waves effectively. Ignoring Radio mode misses a huge percentage of telecom infrastructure.

Can I use a Genny4 with an older C.A.T3?

Technically yes, on the standard 33kHz setting. However, you will lose the benefit of the "Small Diameter Locate" frequency and the "Signal Boost" features. It is highly recommended to pair Generation 4 tools together for maximum sensitivity.

Conclusion

Cable avoidance is a discipline that tolerates no shortcuts. The cost of a CAT and Genny kit is infinitesimally small compared to the cost of a life, a lawsuit, or a repaired high-voltage main. By adopting the "4-Mode" survey mentality, integrating the Genny4 as standard practice, and leveraging the data-logging capabilities of the gC.A.T4+, you protect not just your project's bottom line, but the people who make it happen.

For more detailed insights on specific components, read our guides on Calibration Standards and Overcoming Detection Limitations.

In This Series

Dive deeper into specific topics: