Underground cables
What you need to know
When underground cables are damaged, people can be killed and injured by electric shock, electrical arcs (causing an explosion), and flames. This often results in severe burns to hands, face and body, even if protective clothing is being worn.
Damage can be caused when a cable is:
- cut through by a sharp object such as the point of a tool; or
- crushed by a heavy object or powerful machine.
Cables that have been previously damaged but left unreported and unrepaired can cause incidents.
The HSE booklet "Avoiding danger from underground services[72]" gives guidance on how you can manage the risks of digging near underground cables.
The Electricity Networks Association (ENA) publication "Watch It! When digging in the vicinity of underground electric cables also provides advice".
What you need to do
If you are digging or disturbing the earth you should take care to avoid damaging underground services. Underground electrical cables can be particularly hazardous because they often look like pipes and it is impossible to tell if they are live just by looking at them.
Damage to underground electrical cables can cause fatal or severe injury and the law[73] says you must take precautions to avoid danger.
Excavation work should be properly managed to control risks, including:
Planning the work
Most service cables belong to a Distribution Network Operator (DNO). However, some cables belong to other organisations such as the highways authority, Ministry of Defence or Network Rail.
You should check nearby for equipment owned by the organisations listed above, and if you suspect there are underground cables , ask them for plans to confirm their location. If underground cables are nearby you may need to ask someone from the organisation to come and accurately locate them for you.
If you are excavating near your own cables , then someone who is experienced in underground cable detection techniques should help you locate them using suitable equipment.
You may need to make underground cables dead for the work to proceed safely. Be aware that electricity companies are required to give five days' notice to customers whose supply is to be disconnected.
Careful planning and risk assessments are essential before the work starts. Risk assessments should consider how the work is to be carried out, ensuring local circumstances are taken into account.
Using cable plans
Plans or other suitable information about all buried services in the area should be obtained and reviewed before any excavation work starts.
If the excavation work is an emergency, and plans and other information cannot be found, the work should be carried out as though there are live buried services in the area.
Symbols on electricity cable plans may vary between utilities and advice should be sought from the issuing office. Remember that high-voltage cables may be shown on separate plans from low-voltage cables.
Plans give only an indication of the location, and number of underground services at a particular site. It is essential that a competent person traces cables using suitable locating devices.
Cable locating devices
Before work begins, underground cables must be located, identified and clearly marked.
The position of the cable in or near the proposed work area should be pinpointed as accurately as possible by means of a locating device, using plans, and other information as a guide to the possible location of services and to help interpret the signal.
Remember: Locators should be used frequently and repeatedly during the course of the work.
People who use a locator should have received thorough training in its use and limitations. Locating devices should always be used in accordance with the manufacturer's instructions, regularly checked and maintained in good working order.
Safe digging practices
Excavation work should be carried out carefully and follow recognised safe digging practices.
Once a locating device has been used to determine cable positions and routes, excavation may take place, with trial holes dug using suitable hand tools as necessary to confirm this.
Excavate alongside the service rather than directly above it. Final exposure of the service by horizontal digging is recommended, as the force applied to hand tools can be controlled more effectively.
Insulated tools should be used when hand digging near electric cables.