Construction Guide – Power Cables

Every year, accidents occur on large and small scale construction sites around the country, when due care and attention is not paid to neutralising the threat of un-insulated overhead and underground power cables. Electric shocks, serious burns and, in some instances, even death, can be the result of a lack of care in dealing with power cables.

Many don’t realise the true threat. Electricity at high voltages can jump short distances through the air and overhead pylons can be carrying up to 400,000 volts. This means that equipment does not even need to touch the cables for those on the ground to be potentially severely affected.

Overhead cables can be very difficult to see, particularly against a dark or very bright background, but the danger can be avoided by implementing simple safety measures, as listed below, or by contacting the local Distribution Network Operator and having them divert the power away from cabling in the area – rendering the line “dead”.

It is strongly suggested that you:

• Find out the route of all overhead power lines and underground cables on your site or near your boundaries. Mark them on a site map.
• Arrange access points so that they are well away from overhead power lines.
• Ensure you obtain details of maximum safe working heights underneath the power lines.
• Brief all workers of the dangers of overhead power lines and reference the sitemap when planning construction activities.
• Erect warning notices and posts to provide a physical and visual warning where regular crossing underneath power lines is unavoidable. These should be 9m from wood pole lines and 15m from steel tower lines.
• Plan storage areas well away from power lines. Keep at least 9m (measured horizontally) separation for conductors on wood pole lines and 15m for steel tower lines.
• Display notices for the routes of underground cables and ensure safe excavation techniques are used when working near to underground power cabling.

Even if you have rendered the lines on your site as ‘dead’, contact with an overhead power line may cause the power to ‘trip out’ temporarily and it may be re-energised automatically, without warning.

Your local Distribution Network Operator (DNO) can generally supply stickers describing emergency procedures and containing contact numbers that can be stuck in the cabs of vehicles likely to be used near overhead power lines.

If you’re carrying out work on your own residence and fear you may be too close to an overhead power cable, call your local power distributor. They may be able to insulate the line, allowing for work to continue without major upheaval or hazard.

Making a cable safe does not necessarily mean a significant delay to works. The last site where one of the Chartered Surveyors in the management team had to enact safety procedures, the distributor was on site within 2 days, turning up on a Saturday to make a cable safe.

For additional information, the leaflet called ‘Safe Working near Overhead Power Lines in Agriculture’ and the Electricity Networks Association (ENA) publications ‘Safety Information for Farmers and Agricultural Contractors’ and ‘Watch It! In the Vicinity of Overhead Lines’ provide advice on what to do if machinery or equipment comes into contact with an overhead power line.

The Health and Safety Executive’s website is also a useful source of information:
Information on overhead cabling can be found here.
Information on underground cabling can be found here.

24-11-11