EMFs come from a wide range of sources and vary enormously in the strength of the fields.

plot of field over typical home

This diagram shows how the magnetic field varies over a typical house. The peaks come from the various appliances, and they are superimposed on a low background field, which varies only slightly across the house.




Appliances are present in every home and fields come from everything from your kettle to your TV - even a mobile phone.

A minority of homes in the UK are close enough to an obvious external source for that to be the main source of the background field:

thumbnail photo of transmission pylonAn overhead line



thumbnail underground cable A high-voltage underground cable



thumbnail substation

A substation



But in most homes, the background field comes from low-voltage distribution wiringHouse wiring can sometimes contribute too.

Outside the home, we can experience EMFs in schools, when using electrified transport, and at work.


How fields vary

Field levels

AC and DC

This page and the links from it deal with AC fields - 50 Hz, the frequency of the power system in the UK and Europe.  But see also static or DC fields.