HSE guidance for Great Britain warns that damage to underground electricity cables can cause fatal or severe injury, and says work should be planned, service plans obtained, cables located with a device and marked before digging, and excavation carried out alongside rather than directly above a service, all of which applies when foundations for a conservatory are dug.

Why foundations bring the risk

Conservatory foundations need trenches or pits, and gardens can contain buried services. The Health and Safety Executive (HSE) says that when underground cables are damaged, people can be killed and injured by electric shock, electrical arcs (which can cause an explosion) and flames, often with severe burns to the hands, face and body even where protective clothing is 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, and cables damaged earlier but left unreported and unrepaired can also cause incidents. HSE’s guidance applies in Great Britain. Foundation design is a separate question, covered in the guide to conservatory foundations, ground conditions and trees.

Planning before any digging

HSE says most service cables belong to a Distribution Network Operator, though some belong to organisations such as the highways authority, the Ministry of Defence or Network Rail, and the person planning the work should check nearby for equipment owned by them and, if underground cables are suspected, ask for plans to confirm their location. It may be necessary to ask someone from the organisation to attend and locate the cables accurately. Careful planning and risk assessment are essential before work starts, and plans or other suitable information about all buried services in the area should be obtained and reviewed before any excavation. If a supply must be made dead for the work to proceed safely, HSE notes that electricity companies are required to give five days’ notice to customers whose supply is to be disconnected, so a disconnection cannot be arranged on the day.

Plans are only an indication

HSE is clear that plans give only an indication of the location and number of underground services at a site. It says a competent person should trace cables using suitable locating devices, and that before work begins underground cables must be located, identified and clearly marked. Locators should be used frequently and repeatedly during the work, and people who use them should be thoroughly trained in their use and limitations, with devices used according to the manufacturer’s instructions and kept in good working order. Symbols on cable plans can vary between utilities, and high-voltage cables may appear on separate plans from low-voltage ones, so advice should be sought from the office that issued the plan. If an emergency excavation is carried out and no plans can be found, HSE says the work should be treated as though live buried services are in the area.

Safe digging practice

Once cables have been located, HSE says excavation may take place, with trial holes dug using suitable hand tools as needed to confirm their position. Digging should be alongside the service rather than directly above it, and final exposure of the service by horizontal digging is recommended because the force applied to hand tools can be controlled more effectively. Insulated tools should be used when hand digging near electric cables. Separately, HSE’s excavation guidance lists underground and overhead services among the key issues for any excavation, together with collapse, falling material and people or plant falling in, and says plant and vehicles should not be parked close to the sides of an excavation.

Overhead lines and the domestic client

HSE publishes separate guidance note GS6, “Avoiding danger from overhead power lines”, aimed primarily at employers and employees who are supervising or in control of work near live overhead lines. It is relevant where a mini-digger, delivery lorry or crane may work close to wires above a garden. HSE says the law requires precautions to avoid danger from underground cables and that commercial clients must give contractors information on ground conditions, underground structures or watercourses and the location of existing services. Those client duties are for commercial clients. A householder commissioning a conservatory is a domestic client (see the guide to domestic clients under CDM 2015). Sewer and drain constraints are separate; see the guide to building near or over a drain.

FAQs

Who is responsible for finding buried cables before a conservatory base is dug?

HSE guidance is written for the people planning and carrying out the excavation, who should obtain plans, locate and mark cables and dig safely. For a homeowner, the contractor normally takes on that role.

Can cable plans be relied on to show exactly where a cable runs?

No. HSE says plans give only an indication of the location and number of services and that a competent person should trace cables with suitable locating devices.

The bottom line

HSE guidance for Great Britain sets out the safe approach to digging near buried services: plan the work, obtain plans, locate and mark cables with a device, and dig alongside the service, using hand tools and insulated tools near electric cables. A conservatory installer should be able to explain how these steps will be followed before foundations are dug. This is general information, not health and safety advice for any specific site.

Sources

This guide draws on the following primary sources, current as of 25 September 2026:

• HSE, “Excavation and underground services” (Electrical safety)
• HSE, “Excavations” (Construction safety topics)
• HSE, “Avoiding danger from overhead power lines” (GS6, fourth edition)

Related guides

Compare Conservatories is an independent guide. We may earn a fee from some links; this never affects what we write. This article is general information, not legal or planning advice on any specific property — always confirm requirements directly with your local planning authority.