Helpful video reference. We use Paragon Training's UK health and safety video "CAT & Genny - Safe Use of Cable Avoidance Tools Safety Training Video UK" as the video reference here. Paragon Training is a UK health and safety training company and this video covers the correct procedure in a UK context, including the Health and Safety at Work Act obligations for anyone carrying out ground-breaking or drilling work near buried services.
1. Obtain utility records before you do anything else
Contact the relevant utility companies using a records service. In the UK, you can request drawings from National Grid, the local DNO, Cadent Gas, and your water company. The Linesearch Before U Dig (LSBUD) service consolidates many of these requests. Allow enough lead time - in a domestic setting this is often overlooked, but records frequently reveal cables in positions you would not expect.
Cross-reference any records with the site: look for surface features such as lamp-post feeds, meter boxes, gate motors, and pond pumps that indicate buried cables nearby.
2. Understand the three detection modes
A cable avoidance tool has three detection modes. You must use all three - each finds services the others can miss.
- Power mode - detects the 50 Hz electromagnetic field from live cables. It will find energised cables that carry mains current.
- Radio mode - picks up re-radiated very low frequency (VLF) radio signals that metallic services act as antennas for. Finds de-energised metallic services the power mode misses.
- Genny mode - detects the specific signal your generator (genny) has induced onto a known service, so you can trace exactly where it runs.
Sweep the whole area in power and radio modes first, before you place the genny. This avoids the risk of the genny signal masking another buried service.
3. Apply the genny signal
The signal generator (genny) induces a distinctive radio frequency signal onto a metallic service so the CAT can trace it precisely. There are two ways to apply it.
- Direct connection - connect a lead from the genny to an accessible point on the service (a stopcock, a meter tail clamp, a grounded rod). This gives the strongest, most accurate signal and should be your first choice.
- Induction - place the genny flat on the ground above the known service route, and it induces a signal magnetically. Quicker but less accurate because the signal spreads.
Once the genny is in place, set the CAT to genny mode. Walk slowly along the expected cable route to confirm the route, then proceed to a full area sweep.
4. Sweep in genny mode
Hold the CAT wand vertical and move it slowly across the ground, perpendicular to the expected cable run. The signal peaks directly over a buried service and drops off sharply to either side. This peak-response method gives you the most accurate location.
Do not hold the wand at an angle: a tilted wand shifts the peak response off-centre and gives a false position. Keep it vertical and move it at a steady walking pace.
For depth indication, rotate the CAT by 90 degrees so the wand points forward. Many modern units display an estimated depth reading in this orientation. Treat depth estimates as approximate - ground conditions affect accuracy.
5. Sweep in a grid pattern
A single sweep only finds cables running roughly parallel to your direction of travel. Services can run in any direction, so you must sweep the whole area in a grid.
- Walk parallel passes across the entire area, spaced no more than 500 mm apart.
- Then walk the same area again at 90 degrees to the first sweep direction.
This cross-pattern means cables at any orientation will be crossed by at least one sweep and produce a clear peak response.
6. Mark up every detection
Mark each detected service the moment you find it. Use contractor marking spray (the colour convention in the UK follows PAS 128: red for power, yellow for gas, blue for water, green for telecoms) or stakes with tape. Take a photograph of the marked area showing all detections before you start any digging or drilling.
Record the sweep in your method statement or permit to work log if one is in use. On a domestic job this is often informal, but a marked-up photograph on your phone is far better than nothing.
When to call us
If you are planning any groundworks near the house - new cable runs, pond pumps, EV charger feeds, outbuilding supplies - Richard can advise on where services are likely to run and what protection the buried cable needs. Small advisory calls in Sandwich are £10 per 10 minutes.
Planning groundworks or a new supply in Sandwich?
Richard can advise on buried service avoidance, cable routes and the right protection for outdoor supplies.
Contact Richard