Underground cable strikes cause significant damage across UK sites every year — emergency repairs, project delays, enforcement action, and the very real risk of serious injury. What is less often discussed is what actually causes them. The answer, in almost every case, sits in the pre-excavation survey: the mistakes are made before anyone picks up a tool. Across thousands of courses and on-site assessments, the same four failure patterns repeat in every sector, every contractor, every region.
1. Passive-only surveying
The single most common behaviour behind a strike: an operative scans in Power and Radio, decides the area is clear, and starts digging without ever connecting a Genny. Passive detection picks up signals already present on buried utilities — but a telecoms duct, a gas main or a water pipe will often produce no response in passive modes at all. Without an applied signal, those services remain invisible. This is not a theoretical risk; it is the cause of a significant proportion of all strikes in the UK.
2. Inadequate Genny application
Some operatives do connect the Genny — but only ever use induction, because it is the quickest method. Induction applies a signal to the general area rather than to a specific service; it can couple onto adjacent utilities and give a false sense of security. Direct connection, the clamp and capacitance are all more targeted and produce significantly more reliable results, but they take more knowledge and more time. An operative trained only on induction is missing the methods that matter most.
3. Misreading or ignoring signals
A locator produces readings, displays and tones; interpreting them takes an understanding of signal behaviour, the limits of depth estimation, and the difference between a peak and a null. An operative who cannot read what the locator is saying either misses services entirely or marks them in the wrong place — and a service 30 centimetres from its mark is a strike waiting to happen. On congested sites the risk of misinterpretation only rises.
4. Not consulting plans and documentation
Utility plans are imperfect — often out of date, positionally rough, and missing services. They are still a critical starting point. An operative who has not consulted asset-owner plans is working blind: they cannot cross-reference their readings against known infrastructure, and cannot spot the service that should be there but is not producing a response. Free services such as LinesearchBeforeUDig exist precisely to make this step easy.
What closes these gaps
Training that covers all four locating modes, every Genny application method — direct connection, clamp, capacitance, induction, nulling — signal interpretation and depth estimation, and the role of plans in the survey. And a method that puts the Genny first: apply a known signal, locate it, then use passive modes to find what else is present. Organisations that adopt the Genny-first approach see usage rise consistently, and the number of utilities identified before excavation rises with it.
Before you start digging
- Request plans through LSBUD before the job.
- Have a trained operative survey the site with the Genny and CAT; add GPR where ground conditions or missing records demand it.
- Mark everything found, to the standard colour codes, so the dig team can read the ground.
- Hand-dig within tolerance zones: HSG47 requires excavation within 0.5 metres of a marked utility to be by hand tools only.
Even with the best process, strikes can still occur. When they do, record and report every one — internally and to the utility owner. That record is what turns an incident into a lesson: it shows where training or process needs to improve, and it is the raw material for preventing the next one.
Rewritten for the Bureau from the original. Method drawn from Sygma’s own training material.