Is there a new overhead line or substation being proposed close to where you live? Do you have concerns about potential health effects of these proposals?
If you are in this situation the information included in this section may answer some of your questions. If 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.
Am I exposed to EMFs already?
Yes. Anything which uses electricity produces electric and magnetic fields. This includes our household wiring, appliances and the local electricity distribution system. All of these contribute to background electric and magnetic fields in homes, which for electric fields is around 20 V/m and magnetic fields between 0.01 – 0.2 μT.
more on sources of exposure and levels of fields
And will a new overhead lines or substation increase my exposure?
Yes, if it's close enough.
Both overhead lines and substations produce electric and magnetic fields:
For high voltage National Grid substation, you would need to be within metres or maybe tens of metres of the perimeter to get an elevated field. National Grid would always try to maximise the distance of a proposed substation to homes, and it would be rare be that close in a rural setting, but it could happen in an urban setting. But you would probably be getting a higher field from the lines or cables entering the substation.
More on substation exposures
The electric and magnetic fields from an overhead line would depend on its voltage, the current it could carry, and its design. EMF from overhead lines are highest directly underneath the wires and reduce as you move away from the wires.
Typically an overhead line operating at 400 kV would reduce to the level field found in other homes within about 100 m of the overhead line.
More on overhead line exposures
This distance would be less for lower voltage lines.
More distances for different voltages and different field levels
All sources - both overhead lines and substations - comply with the relevant exposure limits - see below.
Why is there concern?
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.
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. To set against this, mice and rats don’t seem to get disease when we expose them in the laboratory. So overall the science is uncertain.
more on the scientific evidence
The evidence is strong enough for magnetic fields to be classified by the World Health Organization as "possibly carcinogenic". But 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.
more on what expert bodies have said
What exposures are acceptable?
The decisions on what exposures are acceptable is made independently of National Grid and the electricity industry.
The UK Government at a national level set exposure guidelines for EMFs and the electricity system complies with this, including new equipment. The limits are designed to prevent all established effects of fields on the body.
more on policy in the UK
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.
more on exposure limits
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 or substation to achieve compliance, and there are no restriction on how close a property can be to a power line or substation.
Exposure limits - the 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.
So will the overhead line or substation be safe?
All overhead lines and substations 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.
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 balance of evidence is against health effects – and it’s not considered strong enough evidence to restrict such exposures.
But it is for each person and family to decide for themselves how they you feel about this based on the evidence.