High voltage underground cables carry electricity at 11kV, 33kV, 66kV, or 132kV and are found on many UK construction sites near substations, industrial areas, and major infrastructure routes. A strike on an HV cable is almost always fatal due to the massive fault energy released. The safe digging precautions for HV cables are more stringent than for low voltage supplies. This talk covers the additional controls required.
Key Hazards
Fatal electrocution from striking an HV cable carrying 11kV to 132kV
Massive arc flash explosion destroying plant and injuring nearby workers
HV cables at unexpected depths or routed differently from utility records
Ground current travelling through soil injuring workers standing near the strike
Control Measures
Obtain HV cable records directly from the distribution network operator before any excavation.
Request an HV cable crossing agreement or supervision from the asset owner where work is near HV routes.
Use CAT and Genny detection and hand-dig trial holes to confirm the exact position of all HV cables.
Hand dig only within the exclusion zone specified by the asset owner — typically one metre for HV cables.
Never use mechanical excavation within the HV exclusion zone under any circumstances.
Mark the HV cable route on the ground using spray paint and cable route markers after detection.
Brief all operatives and machine drivers on HV cable locations and the enlarged exclusion zone distances.
Ensure the CAT operator holds specific competency for working near HV infrastructure.
Stop work immediately and call the asset owner if any cable is exposed that was not on the records.
Emergency / Rescue
If an HV cable is struck, evacuate everyone at least 25 metres from the strike point immediately. Do not touch the cable, machine, or any person in contact. Call 999 and the asset owner's emergency number. Shuffle away — do not run.
Remember
HV cable records must be obtained directly from the network operator before any excavation
Hand dig only within the exclusion zone — never use mechanical excavation near HV cables
The exclusion zone for HV cables is typically one metre but may be wider as the asset owner specifies
If an HV cable is struck, evacuate at least 25 metres from the strike point immediately
Shuffle away from an HV strike — do not run, as step potential can cause electrocution
Applicable Legislation: Electricity at Work Regulations 1989 · HSG47 (Avoiding Danger from Underground Services) · Health and Safety at Work etc. Act 1974 · CDM Regulations 2015