CAT and Generator Scanning

Over the past 10 years there have been over 1,000 recorded injuries in the UK as a result of contact with underground electricity cables. Over a third of these incidents have been on construction or demolition sites with the remainder on public highways, footpaths, domestic premises and gardens. Damage can result from excavation or penetration of the ground and can cause an explosion leading to severe burns and even death.

The majority of incidents involving service strikes occur because the service locations are either unknown or their assumed positions are inaccurate. Poor working practices and the poor condition of some services add to the chances of damage.

To minimise chances of a strike, four basic processes must be applied and a ‘Permit to Excavate’ system implemented:

  1. Information on all possible services should be collected before work commences- for example utility site plans or use an independent utilities identification company as appropriate.
  2. Assess risk, prepare and brief a Safe System of Work, including the use of excavation permits.
  3. Test and supplement information through thorough site survey and detection using CAT and Genny scans, marking and recording services locations prior to any excavation works.
  4. Manage and supervise work – check work proceeds to agreed methods.


It is identified that:

  • Only using a CAT there is a 40% chance of finding any cables.
  • Using a CAT and Genny (signal generator) the likelihood of finding cables almost doubles to 70%.
  • Having the generator clipped to a lamp post or other utility street furniture further increases the chance to 80%

It is important to note, that no method is 100% accurate. Sample holes and hand digging as far as possible and in known high risk areas is still a must.

Further guidance can be found from the HSE- HSG47 document-

There are several key issues which lead to the striking of live services and the subsequent financial and safety costs:

  • Incorrect/insufficient training- operatives doing the CAT scanning are not competent.
  • Incorrect practice- operatives swinging the CAT scanner, travelling too fast etc
  • Not using a Genny at all times, which greatly decreases the likelihood of finding serves.
  • Insufficient scanning- only small areas have been scanned or the area has not been scanned at all.

Now out on the market there are CAT and Genny devices that will greatly improve the safety and performance of all excavations, they are enhanced by collecting Data on the usage of the equipment which will allow it used to be analysed- including areas scanned and mapped and whether or not use has been in accordance with the correct method, which will enable identification of key areas of concern.

Once training requirements have been systematically identified then a suitable training course should be considered to ensure competence of any person responsible for Cat and Genny scanning.

For further information or if you have any concerns around Cat and Genny Scanning please contact the Office.