Distribution lines are at lower voltages than transmission and are used by Distribution Network Operators for distributing electricity round an area. Some are still on steel pylons but many are wood poles.
more detail on the fields they produce
How do overhead lines produce fields?
The magnetic field produced by a current in a conductor falls with distance from the conductor. Where there is more than one current forming part of one or more electrical circuits, there is also partial cancellation between the magnetic fields produced by the individual currents, and that cancellation generally becomes better at greater distances. Overall, the magnetic field is highest at the point of closest approach to the conductors and falls quite rapidly with distance. Similarly, there is partial cancellation between the electric fields produced by the voltages on individual conductors, and the electric field is usually highest at the point of closest approach to the conductors and falls quite rapidly with distance.
Therefore overhead lines produce a magnetic field which peaks underneath the conductors and falls rapidly with distance either side.
More detail on how fields fall with distance
More detail on the factors that affect the field a line produces
How accurate are calculated fields?
Magnetic fields can be calculated with considerable accuracy if the currents are known.
More detail on calculations including a direct comparison of calculations and measurements
How many people live near high-voltage power lines?
Although people living near high-voltage power lines are a group whose exposure is high and can often be calculated reasonably well, they are a small group. In the UK, 0.07% of homes are within 50 m of transmission lines and 0.21% within 100 m. Percentages in other countries seem to be comparable (USA 1.1% within 40 m; Denmark 0.43% within 75 m), with higher percentages partly reflecting a broader definition of “transmission”.
More detail on numbers of homes near power lines
Averaged over the population, high-voltage power lines contribute only a small fraction of collective average exposure to EMFs, because so few people are exposed to them. The best estimate possible from the UK is that high-voltage power lines contribute 5% of total average population exposure.
