Understanding Pot-Ended & Abandoned Cables: Why They’re Almost Impossible to Detect (And What That Means for Your Site)
Educational guidance for contractors, project managers and site engineers
When you’re planning excavation or construction works, one of the biggest hidden risks on any site is not the services you can see or trace — it’s the ones you can’t. Pot-ended and abandoned cables are a perfect example. They sit underground, look identical to live services, rarely appear correctly on records, and — crucially — do not respond to standard CAT & Genny equipment.
Understanding why they’re so difficult to identify is essential for highways, civils and infrastructure projects across the UK.
Accurate survey control starts with solid on-site setup. Our Lead Site Engineer Ashish Chauhan carrying out precise measurements in Bishops Stortford, Herttfordshire for Bishops Stortford Town Council.
What Are Pot-Ended and Abandoned Cables?
A pot-ended cable is one that has been disconnected and sealed at one end. Once capped, it no longer carries electrical current. Because CAT & Genny equipment relies on electrical or induced signals, these cables instantly drop below the radar:
No Power (“P”) signal
No Radio (“R”) signal
No Genny (“G”) signal (no complete return path)
Abandoned cables present an even bigger challenge. These may have been taken out of service decades ago, partially removed, rerouted or simply left in the ground. Many still appear on old utility drawings despite being inactive — and others never appear at all.
For contractors relying on survey data to plan excavations, these “ghost cables” create uncertainty, delays and potentially unsafe working conditions.
Why Standard Detection Methods Fail
This is the heart of the issue — and the main thing project teams must understand.
A CAT or electromagnetic locator works by detecting current or electromagnetic signals in a conductive cable. But a pot-ended/abandoned cable:
Has no current
Has no earth return path
Often has no accessible point to inject a signal
May be surrounded by multiple parallel services that interfere with readings
Even high-output generators struggle because the induced signal cannot travel along a cable that is electrically open.
This means the equipment is working correctly — the data simply cannot show what isn’t detectable.
As stated in the HSE guidelines on underground services non-detectable utilities are one of the leading causes of service strikes.
Can Pot-Ended or Abandoned Cables Be Found? (The Honest Reality)
In most cases: not reliably.
Some techniques may help in favourable conditions, but none guarantee detection:
1. Passive multi-mode scanning
Occasionally you may detect weak interference from adjacent live cables — but this is inconsistent and site-dependent.
2. Ground Penetrating Radar (GPR)
GPR can pick up the physical presence of ducts or trenches, but:
Clay soils
Reinforced concrete
Deep services
Moisture content
…all severely reduce accuracy. Even in good conditions, GPR cannot confirm whether a cable is live, dead, abandoned or pot-ended.
3. Record research & site observation
Historic plans, redundant cabinets, old jointing pits, telecom markers and legacy service routes offer clues. But records across the UK are not complete, not always accurate, and often decades out of date.
4. Direct access & signal injection
Only possible where a cable is physically exposed — a luxury most sites don’t have.
Why This Matters for Construction Projects
Misidentifying buried services can lead to:
Unexpected obstructions during excavation
Delays while redesigning foundations or drainage
Damage to client relationships
Safety risks if a supposedly “dead” cable feeds another site
The emergence of the National Underground Asset Register (NUAR) is improving records across the UK, but it cannot retrospectively fix decades of undocumented changes.
Understanding the Limits of PAS 128 Surveys
PAS 128 sets out quality levels and detection methods — but even a high-quality PAS 128 survey cannot detect what has no detectable signal.
A responsible utility survey must clarify:
What has been detected
What has not been detected
Where uncertainty remains
Where pot-ended or abandoned cables are suspected but unconfirmed
This transparency helps project managers plan realistic safe-dig strategies rather than relying on a false sense of security.
If you want to learn more about utility surveys you can read more here.
Key Takeaway for Contractors and PMs
Pot-ended and abandoned cables are one of the biggest “unknowns” on UK construction sites. Standard detection equipment cannot locate them — not because the survey was poor, but because these services physically cannot be traced using electromagnetic methods.
The best risk reduction is:
Good pre-construction planning
Clear communication between project teams
Conservative safe-dig procedures
Awareness that survey data will never show 100% of buried services
👉 Visit our Website or call 01279 927 033 to book your next PAS 128 utility survey or to discuss safe-dig planning for upcoming works.