Transmission overhead lines
The largest types of overhead lines used in the UK operate at 400 kV and 275 kV. This website refers to 400 kV and 275 kV lines as transmission voltage, but in Scotland transmission voltage also includes 132 kV lines. The details on 132 kV lines are given on the distribution voltage lines page.
If you live or are buying a home near to one of these types of overhead lines, below are examples of the electric and magnetic fields they produce.
As explained on the ‘What are EMFs’ page, the voltage of an overhead line is fixed, so the electric field is nearly always constant. Magnetic fields are different; they can increase or decrease depending on the current the overhead line is carrying at any time. Because of this, we provide the typical levels of magnetic field that you would expect to measure from these types of overhead lines on any given day. We also provide the maximum magnetic field that each overhead line could produce if it was carrying its maximum current, however, these levels of magnetic field rarely, if ever, occur.
To help identify what voltage an overhead line is operating at, please see the ‘What is near me?’ page. Once you have identified the voltage, the graphs below will give the typical day-to-day EMF exposures that an overhead line produces.
The same pylon designs are used for 275 kV and 400 kV lines and they can carry the same current, so they produce the same magnetic fields. As electric fields are produced by the voltage, the 275 kV lines produce lower electric fields than the 400 kV lines.
