Posted: 4 August 2016

Safer together

National Grid, third party guidance, Electricity Transmission, overhead lines, underground cables, risk, substations, electricity, hazard, safety
Woodhead tunnel summer 09_550x250

Not informing us about work close to our equipment can result in a serious breach of safety, and while it’s easy to see if a pylon is close by, that’s clearly not the case with our high-voltage underground cables.


National Grid’s electricity transmission network operates at up to 400,000V, so it’s a matter of life or death that people working nearby are protected. Overhead Lines and Cables Manager Damien Culley outlines the work he’s doing with developers and third parties to ensure they work safely and responsibly. 

National Grid owns and operates the high-voltage electricity transmission network right across England and Wales. We have 15,000km of overhead lines and 1,000km of underground cables. When your network covers such huge ground, it’s inevitable that developers and third parties will want to carry out work nearby.

In our Electricity Transmission business alone, we receive several hundred of these enquiries a month. It’s not our business to constrain development. But it is our business to keep people safe and make sure work is carried out without disrupting the secure and reliable operation of our network.

So our priorities are straightforward. And we have well-established processes in place to manage enquiries and make sure we find mutually acceptable solutions.

Raising awareness of risks

But there is room for improvement. For example, we still see people going ahead with developments and other works without contacting us. There are also examples of life-threatening near misses, where site workers haven’t been aware that our cables are buried right beneath them. So it’s important we take a responsible and proactive approach to raising awareness of the risks involved – and the steps companies need to take to safely carry out this kind of work.

Let’s start with the basics

Our electricity transmission infrastructure consists of the following:

  • Overhead lines – these are made up of pylons, also called towers, and conductors, also known as cables. It’s essential that a safe distance is kept between exposed conductors, people and objects. These lines operate at voltages of up to 400,000V.
  • Underground cables – a growing feature of our networks. They consist of a live core surrounded by protective insulation and armour. These lines also operate at up to 400,000V.
  • Substations – these are found at points on our network where a rise or fall in voltage is required. They tend to be quite large sites, so it should be obvious to any developer that one is close by.

If a developer or third party is planning any work close to any of these, they need to contact us as soon as possible by phone, email or letter – or by completing their details on a simple automated system. From there, we’ll risk assess your proposals, provide the relevant drawings to locate where our equipment is, and inform you of all the possible risks and hazards involved that you’ll need to build into your plans.

Taken by surprise

Some of these, particularly if you’re new to development, are surprising. Not least the way we measure safety clearances, which are an important consideration for anyone working beneath our power lines.

At the voltages we operate at, it’s possible for electricity to jump several metres from a conductor and kill or cause serious injury to anyone who is nearby. So it’s essential that a safe distance is kept between conductors, people and objects.

What we’ve seen on several occasions is developers underestimating the correct safety clearance. They arrive on site and see our cables sitting high and assume there’s plenty of room for them to work and build. However, we’re legally obliged to assess the clearance distance at the biggest possible sag, which means the lowest possible point it could be from the ground under the biggest power flow on the hottest day.

We’ve seen developers proceed a long way on their project, assuming far greater clearances than they’re actually allowed. This not only makes for a very awkward conversation between us and the developer, it introduces extra costs and delays in making design changes further down the line.

 Other issues, risks and hazards to consider include:

  • Providing access to National Grid – we have existing land rights in place near our assets that allow us to access them for maintenance, repair and renewal. So it’s really important that your designs include a clear corridor for us to work in.
  • Microshocks – large electrical conductors create an electrical field, so anything metallic near to them (within tens of metres) has the potential to pick up a charge. This can cause small shocks to anyone who touches a charged item. While they’re not harmful, they are unpleasant.
  • Induced charges – electrical equipment installed near our equipment can be damaged by induced current, where electrical current flows through it.
  • Fires and firefighting – many people aren’t aware that the fire service may not tackle a fire near an overhead line until National Grid’s engineers have made it safe. In reality, that could delay firefighting for several hours, by which time a building could have burned to the ground. Developers need to factor this into their emergency plans and insurance arrangements.

Not informing us about work close to our equipment can result in a serious breach of safety. While it’s easy to see if a pylon is close by, that’s clearly not the case with our high-voltage underground cables. These could be less than a metre under your feet in the middle of a green park – or at the end of a garden. So it always pays to check with us.

We recently saw someone strike our underground cables with an excavator, because they hadn’t checked on the location of our assets. They cut through the cable’s cooling pipes and missed the high voltage line by a couple of centimetres. If they had done so, it’s likely they’d have been killed.

Staying in control

Put simply, we need to know what work is happening and where in order to stay in control of our operations. If a developer had restricted our access and there was an emergency, we’d have to find a way to get to our towers. If the only way of doing that was by coming in through people’s gardens with HGVs, then we’d have no choice but to do so.

And if, down the line, we discover someone has built something that is too close to our equipment, we have to do remedial work to fix it. This ends up costing the UK consumer – and in some cases the third party – a lot of money. But these are worst-case scenarios. And there’s no reason for them to play out.

Our message to any developer is simple. As soon as you have an idea of what you’re intending to do, use our third-party processes (details below) to tell us what you’re doing and where you’re working. If it looks simple, we’ll be able to give you the location of any risks and provide you with the green light to move forward. If it’s more complex, we may arrange a site visit to talk in more depth about the issues you need to be aware of.

With advance warning, we can help you to factor all kinds of hazards into your designs, which will save you time and money in the long run. We’re not here to stop people doing what they want, but we are here to ensure third parties work safely. We want to be as flexible as we can and facilitate development in the safest possible way.


Further information

You can find out more by downloading our easy to follow guidance for third parties.

To contact us directly, email, call 0800 688 588 or visit the website

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“It’s not our business to constrain development. But it is our business to keep people safe and ensure work is carried out without disrupting the secure and reliable operation of our network”

Damien Culley, Overhead Lines and Cables Manager.