Questions and Answers About EMF Electric and Magnetic Fields Associated with the Use of Electrical Power.
January 1995.

Your EMF Environment

Q. How do electric and magnetic fields from transmission lines and appliances compare?

A. Electric fields close to transmission lines are much stronger than the fields found near electrical appliances. However, remember that electric fields are greatly reduced in strength by objects like buildings, trees, and vehicles. Magnetic fields, on the other hand, are not blocked by most materials. Magnetic fields very close to electrical appliances are often stronger than the fields directly beneath power lines. However, appliance fields decrease in strength with distance more quickly than do power line fields.

In the following tables, all magnetic field measurements are given in units of milligauss (mG), and dashes in columns mean that the magnetic field measurement at this distance from the operating appliance could not be distinguished from background measurements taken before the appliance had been turned on.

Please note: you must be using NCSA Mosaic 2b3 or later or Netscape 1.1 or later to view the tables below.

Some appliances produce both 60 Hz and higher frequency fields. For example, televisions and computer screens produce radio-frequency fields of 10,000-30,000 Hz (10-30 kHz) as well as 60 Hz fields. Microwave ovens produce 60 Hz fields of several hundred milligauss, but they also create microwave energy inside the appliance that is at a much higher frequency (about 2.45 billion hertz). We are shielded from the higher frequency fields but not from the 60 Hz fields.

Sewing machines: Home sewing machines can produce magnetic fields of 12 mG at chest level and 5 mG at head level. Magnetic fields as high as 35 mG at chest level and 215 mG at knee level have been measured from industrial sewing machine models (Sobel 1994).

In the above table, the clocks are electrically powered using AC, as are all the appliances described in these tables. The measurements for baby monitors were taken for the unit nearest the child.

Typical EMF levels for transmission lines are shown in the chart on the next page. At a distance of about 350 ft, at time of average demand, the magnetic field from many lines can be similar to typical background EMF levels found in most homes. As the chart shows, the distance at which the magnetic field from the line becomes indistinguishable from typical background EMFs differs for different types of lines. Neighborhood distribution lines can also sometimes produce significant magnetic fields, depending on the amount of current they carry.