In the UK, commuter trains into London - the old Southern Region - operate at 750 V DC, and the London Underground operates at 600 V DC. In the rest of the country, most electric railways with overhead electrification operate at 25 kV AC, at the same frequency, 50 Hz, as the power system. In other countries, a variety of voltages are used, and some systems use a lower frequency, 16 2/3 Hz.
Exposures come from:
- electric fields produced by the overhead conductor - perhaps a few kV/m maximum on a station platform
- magnetic fields produced by the traction current flowing in the overhead condurctor (or the third rail) and returning in the running rails - perhaps a few microteslas.
- magnetic fields produced by conductors within the train carrying the current to the motors, and perhaps by equipment associated with the motors -sometimes as much as milliteslas close to the floor, but more usually, at waist height, tens of microteslas.
more information on EMFs from trains and published reports
You wouldn't think of a normal petrol or diesel car as a source of EMFs but there are two ways it can happen:
- if the steel bands in the tyres have permanent magnetisation, the rotating tyre then leads to an alternating field - a microtesla or two at the location in the back seat closest to the tyre
- if the alternator and the battery are at opposite ends of the car, the wire connecting them can be a source of field, which is mainly DC but can have an AC component - a few microteslas at certain places in the car.