Underground cable strikes cause significant damage on construction sites across the UK every year. Emergency repairs, project delays, HSE enforcement, and the very real risk of serious injury on site: the consequences are well documented. What is less often discussed is what actually causes cable strikes in the first place.
The answer, in almost every case, sits in the pre-excavation survey. The mistakes that cause a strike are almost always made before anyone picks up a tool to dig. After delivering thousands of cable avoidance courses and carrying out on-site competency assessments across construction projects of every type, Sygma's trainers see the same four failure patterns repeated across every sector, every contractor, and every region. Each one is preventable.
Behaviour one: passive-only surveying
The single most common behaviour behind cable strikes is an operative who scans in Power mode and Radio mode, decides the area is clear, and begins excavation without ever connecting a Genny. Passive detection picks up signals that are already present on buried utilities, but not all underground services carry detectable passive signals.
A telecoms duct, a gas main, or a water pipe will often produce no response in passive modes at all. Without applying a known signal using the Genny, these services remain invisible beneath the ground. This is not a theoretical risk. It is the cause of a significant proportion of all cable strikes in the UK, and a single strike on a high-pressure gas main endangers every worker on site.
Behaviour two: inadequate Genny application
Some operatives do connect the Genny, but only use induction because it is the quickest and easiest method. Induction applies a signal to the general area rather than to a specific service. The signal can couple onto adjacent utilities, producing misleading readings and a false sense of security.
Direct connection, clamp, and capacitance are all more targeted methods that produce significantly more reliable results, but they require more knowledge and take more time. On busy sites where contractors are under pressure to start work quickly, shortcuts with the Genny are common. If an operative has only been trained to use induction, they are missing the methods that matter most.
Behaviour three: misreading or ignoring signals
A locator produces numerical readings, graphical displays, and audio tones. Interpreting these correctly requires an understanding of signal behaviour, the limits of depth estimation, and the difference between a peak and a null response.
When operatives are not trained to interpret what the locator is telling them, they either miss services entirely or mark them in the wrong place. A service that is 30 centimetres from where it was marked on the ground is a cable strike waiting to happen. On congested sites where multiple pipes and cables run close together, the risk of misinterpretation rises and so does the damage it can cause.
Behaviour four: not consulting plans and documentation
Utility plans are not perfect. They are often out of date, lack positional accuracy, and may not show every service present. But they remain a critical starting point for any excavation. Utility companies provide plan information through services like LinesearchbeforeUdig, and consulting these records before you dig is a key safety requirement.
An operative who does not consult asset-owner plans before scanning is working blind. They do not know what should be beneath the ground, cannot cross-reference their locator readings against known infrastructure, and cannot identify services that ought to be present but are producing no response. Plans alone do not prevent strikes, but skipping them removes a safety layer and makes it harder to report what the survey found.
What training does about these behaviours
The purpose of cable avoidance training is not to show someone how to turn on a locator. It is to build the decision-making framework that stops each of these four behaviours from happening on site. A well-structured course covers all four locating modes, all five Genny signal application methods, signal interpretation and depth estimation, and the role of plans and documentation in the survey process.
This is why Sygma's approach centres on the Genny-first methodology. Rather than treating the Genny as an optional extra used if there is time, the training positions it as the default starting point. Operatives learn to apply a known signal first, locate it, then use passive modes to identify additional services. This reversal of the typical workflow catches the services that passive-only surveying misses. The data from organisations that have adopted it is consistent: Genny usage rates increase by 70 to 80% after training, and the number of utilities identified before excavation rises correspondingly.
Not all training delivers the same standard
A half-day refresher that covers the basics of Power and Radio mode with a brief demonstration of the Genny does not address the four behaviours above. Reducing strikes requires hands-on practice with all four modes, all Genny application methods, realistic signal-interpretation exercises, and an assessment that tests whether the operative can apply what they have learned.
The real cost of a cable strike
The costs go well beyond the immediate repair bill. Utility companies typically charge the responsible party for emergency response, repair work, and loss of supply, and those costs can run from thousands to hundreds of thousands of pounds for a single strike on major infrastructure. Work stops while the damage is repaired, and in many cases the team cannot continue until the utility company confirms the area is safe. Insurance claims add further expense and affect future premiums.
The public impact should not be overlooked either. A strike on a water main can flood homes and businesses. A hit on a gas pipe can force an evacuation. Damage to telecoms or electricity can cut essential services to a whole neighbourhood. Every one of these incidents damages trust between contractors, utility companies, and the communities they work in.
Best practice before you dig
Prevention starts before any excavation. Request plans through LinesearchbeforeUdig (LSBUD): a free service that alerts utility network operators to your project location and provides documentation showing the approximate position of their services. Then have a trained operative carry out a full survey with the Genny and CAT. Where ground conditions are difficult or information is thin, Ground Penetrating Radar can add another layer of data.
Mark everything the survey finds, using the industry colour codes so the dig team knows what type of service lies beneath each line. That communication between survey and dig is a core part of strike prevention on a busy site.
Finally, hand-dig within the tolerance zones. HSG47 guidance requires excavation within 0.5 metres of a marked utility to be carried out with hand tools only. Mechanical excavation inside that zone is one of the most common causes of damage, and it is a risk good survey data alone cannot remove.
Reporting and learning from strikes
Even with the best processes, strikes still occur. When they do, the response matters. Every strike should be recorded and reported, internally and to the relevant utility company. That documentation reveals patterns, shows where training or process needs to improve, and provides what insurers and regulators need.
Organisations that are serious about reducing strike rates use this data to target training at the specific behaviours and site conditions causing the most damage. For contractors managing multiple projects, a culture of open reporting and continuous improvement is the most effective long-term protection for the people on site and the services beneath them.
Rewritten for the Bureau from the original. Method drawn from Sygma’s own training material.