Service strikes are still one of the most avoidable causes of life-changing injury, power cuts and project delay. Most incidents don’t happen because people don’t own a locator; they happen because the basics—planning, sweeping technique, and controlled breaking of ground—get rushed. With time pressure, multiple subcontractors and changing ground conditions, small gaps in method turn into big risks.
TL;DR
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– Treat utility avoidance as a planned sequence: plan, prove the kit, passive sweep, active Genny, mark-up, controlled dig, review.
– Never rely on one CAT pass or a single mode; use multiple passes from different angles and use the Genny actively.
– Depth readings are only a guide; confirm with trial holes and safe hand-dig or vacuum excavation.
– Record the mark-up, brief the team, and stop if the picture changes—don’t “chase the detector”.
CAT and Genny: a staged control sequence that prevents strikes
# Build the picture before you switch on the locator
/> Start with reliable utility information from the client, utility providers and recent as‑builts. Overlay plans onto your works area and think in three dimensions: services can be shallow, deep or crossing at odd angles after alterations. Walk the ground with the foreman, spotting obvious clues—covers, cabinets, marker tape, street furniture, recent patching. Define the work zone, set an exclusion zone for the initial sweep, and agree where you will store spoil so you don’t bury your own mark-up.
# Prove the kit is fit and the operator is competent
/> A locator is only useful if it works and the user knows how to read it. Do a function test in a known location (for example, a live streetlight feeder or a cable with a clamp point) and confirm audio/visual responses. Check battery levels, damage to the wand and leads, and that the Genny output is working. Keep evidence of recent calibration or verification from a competent source as good practice, and record who is doing the sweep and when.
# Sweep in passive modes from multiple angles
/> Use passive modes to pick up naturally radiating services, but don’t stop there. Walk the area slowly in parallel passes, then at 90 degrees, keeping the locator head close to the ground without scuffing it. Pause where you get fluctuating signals and triangulate by coming at the point from different directions. Mark suspected routes lightly at first, as provisional, and keep your body and any metal objects away from the head to reduce interference.
# Drive the signal actively with the Genny
/> Passive-only sweeps miss non-radiating assets. Introduce the Genny to push a detectable signal along target cables or metallic pipes. Where it’s safe and permitted, use direct connection for the cleanest signal; otherwise use an induction clamp or surface induction. Work methodically, label which service you think you’re tracing, and avoid coupling the signal unintentionally into adjacent metallic structures like fences or rebar. Confirm the run again from perpendicular angles and extend the trace beyond your immediate dig area.
# Mark, record, and brief the route visibly
/> Once you’re confident in your trace, mark the route and direction with durable paint or crayon, and note key offsets from fixed features. Add a simple sketch to the permit or task briefing: who scanned, what modes used, where the Genny was attached, and known limitations. Brief the digging crew and plant operator together; make sure everyone knows where not to put the bucket, where trial holes will go, and where the spotter will stand.
# Break ground with trial holes and controlled methods
/> Depth indication on a locator is a rough guide only. Prove the service location and depth with hand-dug trial holes or vacuum excavation at planned points along the trace, starting outside the expected line and working towards it. Use insulated tools, maintain exclusion zones, and set a clear stop rule if the trial hole doesn’t find what you expect. Keep the plant away until services are proven and exposed, and get temporary support or edge protection in place if you’re forming an excavation that introduces fall or collapse risks.
# Stay live to change: monitor, pause, escalate
/> Conditions move: rain increases conductivity, a generator starts up nearby, or the route turns unexpectedly. Keep the locator on hand during the dig, rescan as the ground opens up, and extend the mark-up as needed. If the sweep picture degrades, the mark-up doesn’t match what’s exposed, or anyone loses confidence, stop and escalate to the supervisor. Update the permit and briefing before restarting.
Common mistakes that still bite teams
# Relying on one quick pass in power mode
/> A single, brisk sweep only sees what happens to be radiating at that moment. It misses dead or balanced services and gives a false sense of security.
# Reading depth as gospel
/> Depth indication varies with ground, signal strength and technique. Treat it as a hint, not a measurement, and always prove by exposing.
# Skipping the brief because “it’s only a small hole”
/> Most strikes are in shallow, localised digs for posts, bollards or kerbs. The smaller the hole, the more tempted people are to skip the sequence.
# Treating the permit as paperwork, not a control
/> A permit that isn’t tied to a fresh sweep, a visible mark-up and a toolbox talk is just a signature. Make it a live document that controls the task.
On a wet housing plot: the near-miss nobody wants
/> A groundwork gang on a mixed-tenure housing site were installing kerb edgings at the end of a long week. The supervisor had utility plans from pre‑start, but a drainage re‑route had been installed two months earlier and the latest as‑built hadn’t been issued. The operative did a quick CAT pass in power mode, picked up nothing and set the mini‑digger to scrape a shallow trench. The bucket clipped a cable that arced against the edge of a gully pot but, by luck, didn’t make full contact. Work stopped, and a full sweep with the Genny showed a diverted low‑voltage cable only 150 mm off the kerb alignment. A direct connection at a nearby cabinet would have lit it up earlier; trial holes would have confirmed the offset. The team re‑planned, used vacuum excavation for the crossings and finished without further drama—but it could easily have been a strike with injury and a shutdown.
Supervisor walk-round: utility avoidance essentials
/> Before any break‑ground task, a short, structured walk-round keeps the controls honest. Use these prompts to anchor your briefing and permit.
– Confirm you have the latest utility info and any recent as‑builts covering your exact work area.
– Watch the operator prove the locator and Genny on a known source and record who did the sweep and when.
– See a passive and active sweep done from multiple angles, and ask the operator to explain each signal.
– Check the route is marked clearly, with offsets to fixed features and a sketch attached to the permit or RAMS.
– Agree trial hole locations and method, including insulated tools, vacuum excavation where suitable, and stop rules.
– Set and signpost exclusion zones for plant and pedestrians, including a designated spotter position and spoil storage.
What to keep an eye on across UK sites next
/> Clients and principal contractors are increasingly asking for evidence of locator competence and proof-of-use, including simple logs or data downloads where the kit supports it. Expect more emphasis on vacuum excavation as a default around congested corridors, and closer scrutiny of how permits link to live mark-ups and toolbox talks. Temporary works interfaces also matter: if you’re shoring or forming openings, coordinate with utility avoidance so edge protection, lighting and access don’t obscure your service markings. Where utilities are diverted late in the programme, demand updated records before you lift a spade.
Bottom line for digging around live services
/> Service avoidance is a sequence, not a gadget. Follow the steps, make the picture visible to the whole crew, and stop when the picture doesn’t make sense. That’s how you keep people safe and the programme intact.
FAQ
# How often should we rescan during a dig?
/> Rescan whenever the layout changes, you move into a fresh area, or the ground conditions alter your readings. Keep the locator at the excavation edge and repeat short, focused sweeps as you progress. If the trace shifts or fades, pause and reassess before digging further.
# Do we always need a permit to break ground?
/> Where a site system uses permits, treat them as a core control for any intrusive work, however small. The permit should tie together latest utility info, the sweep evidence, mark-up, and the planned method for trial holes and excavation. If a permit isn’t available or the conditions have changed, don’t start.
# Are depth readings on a CAT reliable enough to avoid trial holes?
/> Depth readings are only indicative and can be skewed by soil type, nearby metalwork and signal quality. Use them to inform where to place trial holes, not as a decision to skip them. Always prove services by exposing them in a controlled way before bringing in plant.
# What’s the safest way to use the Genny around live electrical cabinets?
/> Only connect directly if your method statement and competence cover it and you can do so safely without exposing live parts. If direct connection isn’t suitable, use a clamp around identified cables or induction away from sensitive equipment. Keep your connections tidy, label what you’re tracing, and avoid creating trip hazards with leads.
# How do we manage interfaces with other trades during utility avoidance?
/> Coordinate the sweep and mark-up before other trades set up barriers, storage or scaffold that could hide markings. Brief adjacent teams about exclusion zones and no-go areas, and include service routes on daily coordination boards. If another trade’s activity obscures or alters your controls, stop and re-establish the picture before continuing.
