Groundworks and refurb digs remain some of the most strike-prone activities on UK sites. Buried cables, gas, water, comms and private feeds are often exactly where you don’t expect them, and a rushed scan or a flimsy permit can leave an operator gambling with luck. Cable avoidance tools and signal generators are essential, but they are not a magic wand. The difference between a clean dig and an incident is usually preparation, supervision, and sticking to a simple, repeatable system.
TL;DR
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– Get the permit right: up-to-date plans, marked-up survey, competent scanner user, and hold points before plant touches ground.
– Use CAT and Genny together, in multiple modes, and prove the kit works with a known source before and after scanning.
– Hand dig and trial hole to confirm every marked service; don’t rely on depth estimates.
– Stop and escalate whenever the picture changes: unexpected readings, damaged marker tape, or plans that don’t match the ground.
Hazard picture and control basics in plain English
/> Most services sit shallower than you’d hope and rarely travel in a perfectly straight line. New ducts are installed around old assets, and private spurs are common in industrial yards, schools, retail parks and refurbs. Good practice is to build your dig around layers of certainty: current utility plans, a competent CAT and Genny scan, surface mark-up that everyone can read, and trial holes to visually confirm.
CAT devices detect electromagnetic fields; on their own they can miss dead cables or non-energised metalwork. A Genny applies a signal, either by direct connection, clamp or induction, making more assets “visible” and helping you trace the route. Use multiple modes on the CAT (e.g. power and radio) and then use the Genny to positively locate and trace. Treat depth readings as an indication only, never permission to excavate by machine.
Once you think you’ve found a service, mark it clearly with an agreed colour code and arrows showing direction. Agree a hand-dig zone either side of any suspected line; small changes in alignment are common. Trial holes should be controlled: short sections, insulated hand tools, and no flicking chunks of ground towards plant or people. Vacuum excavation is increasingly used to prove around congested corridors or where brittle fibre is suspected. Always build in a stop point when the ground picture differs from the paper or from your earlier scan.
How a good permit to dig runs on site
/> A strong permit is a coordination tool, not a clipboard exercise. The supervisor requests the permit, compiles current plans, photographs the work area, confirms CAT/Genny competence and checks calibration/functional test. A competent person then surveys the area, scanning in a grid and along likely routes, and marks the ground and surrounding features. The RAMS and permit together state how the excavation will proceed, which sections are hand-dig only, what the hold points are, and who can authorise a change.
Before plant starts, the operator, banksman and ganger attend a point-of-work brief at the marked area. They walk the lines, confirm no new obstructions, and agree signals and exclusion zones. During the dig, the banksman watches the bucket path relative to markings, and trial holes are opened ahead of the machine face. If the weather, lighting or ground conditions deteriorate, the permit stands the team down until the controls still make sense.
Scenario: On a civils job tying new drainage into a retail park, the crew had plans showing LV electric and water on the footpath. The scanner found the expected LV, plus a weak, intermittent line roughly perpendicular to the trench. The team used the Genny clamp on a nearby cabinet and confirmed a live telecoms duct running across the dig area that wasn’t on the drawings. They added a hand-dig zone and requested vacuum excavation for the crossing. Midway through exposing the duct, the banksman spotted marker tape in a slightly different position than the mark-up; work stopped and the supervisor re-scanned. The fibre duct had dog-legged around an old tree pit. Because the hold points were respected, the trench alignment was adjusted without damage and programme recovered by the end of the shift.
Pitfalls and fixes on live digs
/> Rushing the scan is the most common weakness. A proper sweep is slow and methodical, covers a wider area than the trench footprint, and repeats after obstructions (skips, parked plant, steel plates) are moved. Battery condition, earpiece use and environmental noise matter; if the user can’t hear the tone, they’ll miss the cue to stop.
Plans are helpful but often incomplete. Use them to form a hypothesis, not to justify a shortcut. Treat private feeds with caution around compressors, portacabins, EV chargers and lighting columns. Make time to trace back to an origin if a line appears from nowhere.
Temporary works and service strikes are connected. Edge collapse or a rushed benching can push spoil or plant onto a marked line. Build shoring decisions into the permit, and keep the trench narrow where services are expected. Segregation is non-negotiable; a banksman focused on pedestrians can’t also protect the bucket from services.
# Common mistakes that lead to strikes
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Scanning only once and in one mode
One pass in power mode misses dead or lightly loaded assets. Multiple modes and a Genny-assisted trace improve the picture.
# Treating depth as fact
/> Depth readouts are affected by ground conditions and signal quality. Use them as a clue and always verify by hand.
# No functional test of the CAT and Genny
/> Starting the day without proving the kit on a known source invites silent failure. Record a pre- and post-use check to catch faults and defend your process.
# Lifting services out of the way
/> “Just moving the duct a bit” creates strain, cracks joints and can trigger delayed failure. Support exposed services and agree temporary protection with the asset owner if relocations are required.
# This week’s strike-prevention moves
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– Walk the next planned dig route with the supervisor, plant op and scanner user; agree the grid pattern and the hand-dig extents before the permit is signed.
– Prove the CAT and Genny with a known signal source, fit fresh batteries, and inspect leads and the clamp for damage.
– Clear surface clutter that masks signals: move pallets, remove steel plates and relocate parked plant before the scan.
– Mark services on both the ground and vertical features; photograph the layout and add it to the permit pack for the shift brief.
– Set hold points at every crossing and change in service direction; no machine digging past a hold point without the supervisor present.
– Line up vacuum excavation or extra hand-dig labour now for congested areas so the programme doesn’t force a compromise.
– Confirm emergency arrangements: who isolates, where the shut-offs are, and the stop-work trigger words everyone will use.
Fixing the basics of behaviour and supervision
/> Supervisors should stay close to first bucket in ground and any time a marked line is approached. Rotate the scanning role to someone competent if fatigue or noise creeps in. Don’t let pressure to “get it open” bypass the hold points; they are the moments that prevent strikes. Keep photos and sketches up to date as the trench opens, and feed anything new back into the permit so the night shift or follow-on trade inherits a true picture.
Service strikes are still seen as bad luck on many jobs. They aren’t. They are the visible end of soft controls and hurried coordination. Expect clients and principal contractors to push for evidence of competence, better records, and clear stop-work authority on excavations. The bottom line: when the ground is uncertain, slow down, scan again, and dig like there’s a live cable under every spade.
FAQ
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Who should issue and control a permit to dig on a UK site?
A competent supervisor or manager acting for the party in control of the work normally issues and monitors the permit. They coordinate plans, scanning, mark-up and hold points, and make sure the RAMS and permit line up. The person signing must have authority to pause the job when the picture changes.
# How often should we scan with a CAT and Genny during an excavation?
/> Scan before the permit is approved, again after clearing surface clutter, and repeat at each stage where the dig face advances or the setup changes. If weather, lighting or plant positioning alters, re-scan. Treat every crossing and change of direction as a fresh decision point.
# Do we need vacuum excavation, or is hand digging enough?
/> Hand digging with insulated tools is the baseline for proving services, especially at crossings and within agreed offsets. Vacuum excavation is useful in congested corridors, around brittle or high-value assets, and where hand digging is too slow or risks damage. Choose the method that gives you control without forcing the crew to take risks to keep pace.
# What records should we keep during the dig?
/> Keep marked-up plans, photos of the ground markings and exposed services, pre- and post-use CAT/Genny checks, and a copy of the brief attendees and hold points. Sketch any deviations found and add them to the permit pack. These records help you manage the job safely and defend decisions if challenged.
# When should we stop work and escalate?
/> Stop immediately if the scan throws up an unexpected signal, if plans and ground don’t match, if you expose marker tape or a duct where none was expected, or if the kit faults. Escalate to the supervisor or permit issuer and re-plan the dig before continuing. It’s better to lose an hour than to own a strike.
