Is there scientific evidence of adverse health effects due to AC magnetic fields? Yes. Researchers have found health effects, including a doubling of leukemia rates associated with living in AC magnetic field strengths greater than 4.0 mG:
The Swedish National Energy Department issued an advisory warning that schools, playgrounds, and day-care centers should not be sited near power lines, and that children should not be subjected for long periods every day to AC magnetic fields over 3.0 mG.
The main sources of long-term exposure to high AC magnetic fields are: power lines, improperly wired homes, nearby appliances and wiring. In most homes it is possible to reduce exposure by locating beds, work, and play areas where AC fields are low, below 1.0 mG.
What are government limits for AC Magnetic Field exposure? The USA has no federal legal limits for exposure to 60 Hz magnetic fields.
Standards from ANSI-IEEE and WHO-ICNIRP allow even higher exposure.
What are "AC" and "EMF"?
"AC" is "Alternating Current" which is the electrical power (50 Hz and 60 Hz) used in homes and buildings. This emits AC magnetic fields.
What are mG and uT ? These are units of magnetic field strength, measured using a gaussmeter: mG means “milligauss” and uT means “microtesla.” You can leave the meter set to read in mG. Or if your meter reads in uT then 1 uT = 10 mG.
How do I measure AC Magnetic Fields in the home? You can use an AC gaussmeter such as the Bell-4180. It is accurate and easy to use: just push the ON button, wait 10 seconds while it starts, then read the magnetic field strength shown on the screen in mG (or in uT if you prefer). It is a triple-axis gaussmeter which is much easier to use than single axis gaussmeters. Quick-start directions are included with the meter.
What are AC magnetic field levels in a typical home? Houses usually measure between 0.2 to 1.0 mG at most locations in the house away from appliances and wiring. Apartments and condos are usually a bit higher. So beds and play areas can be located where these fields are low, for example below 1.0 mG.
Some locations in the house will read higher due to nearby appliances or wires in the walls or floor. The readings may vary depending on the appliances in use and the exact location tested. Near the home's electric meter, fuse box, and “drop line” will show especially high fields since the electric current to the entire house passes through there. The "drop line" is the thick cable bringing power from the street to the electric meter and this cable is often seen along an outside wall of the house. A bed or pillow could be getting high fields from proximity to the drop line since magnetic fields go through practically all wall materials. Beds or places where people spend a lot of time could be moved to where fields are lower.
Why are AC magnetic fields much higher in some houses? The most common reason is improper wiring connections that were not wired according to the National Electrical Code (NEC). The problem is most common in old houses that have been re-wired, or if the electrician didn’t follow the NEC correctly. It can result in unbalanced currents which cause high magnetic fields, usually over a large part of the house; all the outlets and appliances usually still work, and the magnetic fields are invisible. If a gaussmeter shows high fields, then turning off the main breaker for the house will determine whether the high fields are coming from wiring inside the house. Correcting wiring problems can be very time consuming and expensive. We offer a book and DVD to help electricians fix this problem.
Close proximity to fuse boxes, or cables in walls or floors that carry large currents can also produce high magnetic fields, especially in large office or apartment buildings or dormitories. Some appliances also emit high fields and can be located away from beds.
Proximity to an overhead power line increases magnetic fields in nearby houses, sometimes hundreds of feet away. Exposure will depend on distance, and on the amount of current on the power line which may vary seasonally or with time of day.
What about the Earth’s magnetic field? That is a static magnetic field which people have lived in for millions of years. It is not the same as AC magnetic fields from AC electricity which has only recently become widespread since electrical power has been in use.
What types of EMFs are there? “EMFs” usually refers to one or more of the following:
(a) AC magnetic fields from building wiring, appliances, and power lines. These are not stopped by walls.
(b) Radio Frequency (RF) electromagnetic fields, which are described on our page about RF fields.
(c) Sometimes EMFs can also refer to the electric fields at AC frequencies. These are reduced by many types of walls including wood, brick, and aluminum. It is also more difficult to measure accurately since it is changed by many nearby objects such as body of the person making the measurements. Most of the EMF concerns and epidemiological research has been in regards to the AC magnetic fields and the RF fields (a) and (b) above.
What units are usually used to measure these electromagnetic fields (EMFs)?
For (a): AC Magnetic field in milligauss (mG) or microtesla (uT) (1 mG = 0.1 uT).
For (b): RF field in V/m or Watts per square meter (W/m2) or similar units, and average W/m2
For (c): AC Electric field in Volts per meter (V/m)
Which meter should I use?
For (c) you can use the Electric Field Sensor accessory with the MSI-95. However, most people don’t bother with measuring the low frequency electric field, for the reasons stated in (c) two questions above.
Why do we recommend triple-axis gaussmeters? Triple-axis AC gaussmeters like the Bell-4180 or Bell-4190 are easier to use, much faster, and therefore result in more accurate measurements. Single-axis gaussmeters need to be rotated in various directions which is slow, and often results in reduced accuracy due to not rotating it to the best orientation.
Can the AC gaussmeters measure magnets or the Earth's magnetic field? No, they do not measure those static magnetic fields.
© 2014 Magnetic Sciences