Electricity – underground cables

What you need to do

Damage to underground electrical cables can cause fatal or severe injury and the law says you must take precautions to avoid danger.

This can be achieved by a safe system of work based on planning, use of plans, cable locating devices and safe digging practices.

These four elements complement each other, and should all be used when working near buried cables.

What you need to know

Injuries are usually caused by the explosive effects of arcing current and associated flames resulting in severe, potentially fatal, burns to the hands, face and body.

This can occur when a cable is:

  • penetrated by a sharp object such as the point of a tool; or
  • crushed severely enough to cause internal contact between the conductors or between metallic sheathing and one or more conductors.

Incidents may also arise from cables that have been damaged but left unreported and unrepaired.

Planning the work

The project client with the help of the principal designer (where one exists) must provide relevant information (known as pre-construction information) to designers and contractors about underground services so that they can plan the work to eliminate or reduce risks.

Most service cables belong to the regional electricity company. However, it is possible that some cables belong to other bodies eg highways authority, Ministry of Defence or Network Rail.

You may need to make dead for the work to proceed safely. Electricity companies are required to give five days' notice to customers whose supply is to be disconnected.

Careful planning is 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.

Where it is not possible for those undertaking the excavation work to obtain information eg emergency work being undertaken, the work should be carried out as though there are 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, configuration and number of underground services at a particular site. Subsequent tracing by locating devices is essential.

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 position and route, excavation may proceed, with trial holes dug using suitable hand tools as necessary to confirm the position.

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.

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