The flow of electricity through a conductor produces both an electric and magnetic field around the conductor. Collectively, these two fields are referred to as an electromagnetic field or EMF. The strength of the electric field is measured in volts per meter and varies with the amount of the source voltage. The higher the source voltage, the higher the strength of the field. Electric field strength decreases rapidly with distance from the source.
Electric fields are produced both naturally and by any conductor carrying electricity. The strength of the earth's natural electric field varies, but on average is about one-thousandth of a volt per meter. Electric field strength typically varies from 10 to 150 volts per meter under electric distribution lines and 5 to 100 volts per meter inside homes and workplaces.
The strength of a magnetic field is typically measured in units of gauss or milligauss and varies with the amount of current moving through a conductor. Lines or devices requiring high levels of current flow produce stronger magnetic fields than those with low current flow. For example, the measure of a magnetic field directly under a high voltage transmission line is somewhere between 20 to 650 milligauss. The magnetic field measured underneath a lower power distribution line is .5 to 30 milligauss.
Magnetic fields produced by electrical circuits drop off rapidly with distance from the source. The magnetic field produced by a microwave at 1 foot is 70 to 100 milligauss while at five feet away, the magnetic field strength drops to five milligauss.
Electric fields are blocked by shielding such as walls, houses, trees, other vegetation, soil, and other large dense objects. Magnetic fields, on the other hand, pass easily through most objects and are only blocked by structures containing large amounts of iron or iron alloy metals.