What are the Electro-Magnetic Fields from overhead lines and cables?

As part of the European Union’s energy strategy, there is a commitment to reducing the social and environmental risks associated with the transmission of energy and in this respect cables can provide benefits as they have been shown to be more effective in mitigating potential health impacts.

With cables, the electric field is eliminated whereas for OHLs, the maximum exposure under a line is around 5000V/m falling to around 50V/m at 100 metre distance. Both OHLs and UGCs produce a magnetic field. The magnetic strength at 1 metre above ground directly under a 400kV OHL is approximately 30 μT (microteslas) at normal load and up to 70 μT at maximum load. At 100 metres distance these rates fall to around 0.2 μT and 0.4 μT respectively. Although UGCs can produce higher magnetic fields directly above them than an OHL these fall rapidly such that 10 metres either side of the cable the magnetic field is negligible. For OHLs, the magnetic field is not negligible until some 150-200 metres away from the line.

Cables can therefore be placed in closer proximity to dwellings than OHLs. In some cases, where special screening devices are applied, cables can be installed within 2-3 metres of properties which is not possible with OHLs. Cables do not therefore have an impact on property values whereas studies have shown that the pylons and conductors of an OHL do have a negative impact. A recent study from Oxford Brookes University into the impact that 275kV pylons in a housing estate in Glasgow and 132kV pylons in a housing estate in Worcester had on house prices concluded that property values can be reduced by up to 20 percent if a pylon is situated within 150 metres of a property.