Are you Buying, Selling or Living in a house near to an overhead line and need to know about Electric and Magnetic fields?
If the answer to this question is yes, the chances are that you need to learn about EMFs quite quickly. The information on this page may be of use to you.
We hope that this page answers all your questions but should you find that you need more information on EMFs then you can discuss your specific questions with a professional EMF Advisor by contacting the EMF Helpline. You may also find our booklet EMF The Facts helpful.
This page is about overhead lines – see the parallel page on living near a substation
EMFs are all around us
Electric and magnetic fields are produced wherever electricity is used – they are around us all the time in modern life. Overhead power lines – specifically, the wires, not the pylons that hold them up – are a source but they are only one source.
More on where exposure comes from
Electric fields are produced by voltage and magnetic fields by current. Where there are concerns, they are mainly about magnetic fields.
Most people get most of their exposure to EMFs from the distribution wires along the street and from wiring in the homes. We also get short-duration higher field exposures when we pass close to electrical appliances. Outside the home, we can experience EMFs in schools, factories, offices, when using electrified transport, and when we are out shopping.
In the population as a whole, not many people live close to (say within 100 m) a high-voltage power line. But for those who do, this will also be a significant source of exposure.
Field levels in numbers
We measure magnetic fields in a unit called “microteslas” (µT).
In homes not near power lines, the magnetic field in the general volume of the home can range anywhere from 0.01 µT to 0.2 µT. This will usually come from the wiring along the street that supplies electricity to the home.
Close to electrical appliances in the home, the magnetic field can be tens or even hundreds of µT. But this is only very close to them, the field usually drops away over the first metre or so or even less, and we don’t usually spend extended periods of time that close to them.
Directly under a high voltage overhead line, the average field would be about 5 µT. Theoretically, it could be as high as a hundred, but in practice you virtually never encounter more than 20 µT. The field usually drops off to the 0.01 µT to 0.2 µT you find in ordinary homes within about 100 m.
Why are people concerned?
Over the last 40 years there have been suggestions that magnetic fields, at the levels produced by overhead lines, may cause diseases, principally childhood leukaemia.
More on these suggestions
The evidence for this comes from epidemiology studies (the study of statistics about disease), which have found a statistical association – an apparent two-fold increase in leukaemia incidence, from about 1 in 24,000 per year up to 1 in 12,000 per year, for the children with the top half-percent of exposures.
But to set against this, mice and rats don’t seem to get disease when we expose them in the laboratory, and that’s quite a strong piece of evidence against. So overall the science is uncertain.
The evidence is strong enough for magnetic fields to be classified by the World Health Organization as “possibly carcinogenic”. But that’s a fairly weak classification. Because these studies only show statistical associations and do not demonstrate causation, and because the evidence from the laboratory (biology and theoretical science) is against, the risk is not established, it remains only a possibility.
Ahlbom,UKCCS and Draper – some of the key studies
These are some of the key specific studies on magnetic fields and childhood leukaemia that you may hear mentioned.
The “Ahlbom” study (2000) was an important pooled analysis – it pooled together the results from a number of individual studies from different countries. It really established the idea that there is a statistical association with fields above 0.4 μT. There have been other pooled analyses since which have mainly reinforced this finding.
The UKCCS (1999) was one of those individual studies, conducted in the UK. On its own, it didn’t find much of an association, but it contributed to the overall finding.
“Draper” or “CCRG” (various papers 2005-2014) is a slightly different study – it looks specifically at high-voltage power lines. It found an association – but one that extended too far from the lines to be attributable to magnetic fields, and which declined over the decades from the 1960s to the present. This suggests that whatever is going on, it may not be magnetic fields. And there seems to be no association in the last couple of decades.
What field levels are we talking about?
The statistical associations from the epidemiology studies seem to show up at fields above 0.4 microteslas. (Sometimes people talk about 0.2 microteslas instead.)
How many UK homes does this apply to?
The great majority of homes in the UK have fields less than these values. About 1.5% of UK homes have average fields greater than 0.2 µT and about 0.4% greater than 0.4 µT. These percentages of homes with higher fields are actually smaller than in many other countries.
Only about a half of homes in the UK with fields above 0.4 µT get that exposure from high-voltage power lines – in the rest, the field probably comes from the distribution system or house wiring. But if you do live close enough to an overhead line, that will give you a higher exposure.
EMF policy in the UK
The UK Government at a national level set exposure guidelines for EMFs and the electricity system complies with these. The limits are designed to prevent all established effects of fields on the body.
More on policy and exposure limits in the UK
Policy and exposure limits are ultimately set by the Government.
The limits we follow in the UK stem from an international body ICNIRP and are the same ones set by the EU and used in many other countries round the world.
The guidelines for public exposure are expressed in volts per metre (V/m) for electric fields and microteslas (µT) for magnetic fields. We ensure that all power lines comply with these values even directly underneath them – there is no need for any extra “safe distance” between a property and an overhead line to achieve compliance, and there are no restriction on how close a property can be to a power line.
The exposure limits in numbers
The exposure limits have “reference levels” and “basic restrictions”.
Often it’s sufficient just to look at the “reference levels”:
- Electric fields: 5 kV/m
- Magnetic fields: 100 µT
But the actual limits are given by the “basic restrictions” which are a bit higher:
- Electric fields 9 kV/m
- Magnetic fields: 360 µT
These apply in areas where people spend significant periods of time.
What sort of overhead line is near me and how near is “near”?
Overhead lines range from lower-voltage lines (we call them “distribution lines”) on wood poles to higher-voltage lines (“transmission lines”) on lattice steel pylons.
Work out what sort of overhead line you have from these pictures:
(or see our more comprehensive pictorial guide)
Lower voltage – 132 kV – medium sized lattice pylons
If you live near a distribution line (wood poles, or small pylons): these don’t ever produce fields of 0.4 µT, or perhaps immediately underneath them – almost certainly, you will not be getting these exposures from one of these lines.
At the other extreme, if you live near a transmission overhead line (large pylons): on average it will be elevating the field within a hundred metres or so, and it may be producing 0.4 µT within sixty metres.
In between these: if you live near an intermediate-voltage line (say 132 kV on medium lattice pylons), the distances will be reduced – perhaps 0.4 µT within a few tens of metres.
Is it safe?
All overhead lines comply with the exposure limits, and remember, these exposure limits are set by independent international experts, not by us in the electricity industry – we just make sure all our lines comply with them.
But what about below the exposure limits?
There is some evidence of a possible risk of childhood leukaemia below these exposure limits, at levels produced close to some overhead lines. This is just a possibility – we’d probably say the weight of evidence is against health effects – and it’s not considered strong enough evidence to restrict such exposures. It is for each person and family to decide for themselves how you feel about this based on the evidence.
Recognising that there is this possibility, the UK has also adopted an extra precautionary policy for overhead lines on top of the exposure limits – an aspect of the design of the line called “optimum phasing” – and this reduces the magnetic field below the level it would otherwise be.
Buying and selling a house
A nearby overhead line will be one of many factors you’ll want to take into account when considering a house, just as you would any nearby roads or railways lines, or industry, or anything else in the area. Some people may be put off, but the evidence is that houses near overhead lines do still sell.
Survey reports, mortgages etc
A surveyor may point out the presence of a line in a survey report and may even allude to possible health effects. But they should not recommend refusing a mortgage, and whilst mortgage lenders always have the right to make individual assessments, and some mortgage lenders may choose to specialise in different bits of the market, there is no widespread general policy against mortgages on homes near lines.
Sometimes, an automated online environmental search for a property may report the presence of a power line – see more on these and how to interpret them.
Getting more help
Contact the EMF Helpline – we can talk you through the specifics of the line that affects you and answer further questions about the evidence on health or the UK policy position.