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AC Magnetic Fields in Homes

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. 
In 2009, a scientific panel met in Seletun, Norway and recommended a 1 mG exposure limit based on risk for leukemia, brain tumours, Alzheimer‘s, ALS, sperm damage and DNA strand breaks.
The main sources of long-term exposure to high AC magnetic fields are: power lines, improperly wired homes, and nearby appliances and wiring. In most homes it is possible to reduce exposure by locating beds, work, and play areas where AC fields are below 1 mG. 
What is a typical AC magnetic field level in a home?  Inside a house usually measures about 0.2 to 1.0 mG if not very close to appliances or wiring. Apartments and condos are a bit higher. Beds and play areas can be located where the fields are low, for example below 1.0 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. Instructions for use are included with the meter. 
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. 
What are "AC" and "EMF"?  
"AC"  is "Alternating Current" which is the electrical power (50 Hz and 60 Hz) used in homes and buildings, it emits AC magnetic fields. 
“EMF” is “Electromagnetic Field”: it refers to AC fields described on this page and measured using an AC Gaussmeter, and "EMF" can also refer  to Radio Frequency electromagnetic fields measured using an RF meter
Why do some locations within the home measure higher AC magnetic field levels?  Due to nearby appliances or wires in the walls or floor the readings may vary, depending on appliances in use and the location tested. Some appliances emit high fields and can be located away from beds. 
Close to the home's “drop line” will also show high fields since the electric current to the entire house passes through the "drop line". It 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. Magnetic fields go through most walls, so a bed or pillow can be exposed to high fields within a few feet of the drop line. Beds and places where people spend a lot of time could be moved to where fields are lower. 
Other electric cables in walls or floors that carry large currents can also produce high magnetic fields, especially in large buildings like apartments, offices, and dormitories.
Fuse boxes (circuit breakers), electric meters, and transformer boxes also produce high fields, which can pass through walls.  
Why are AC magnetic fields much higher in some houses? Proximity to an overhead power transmission line increases magnetic fields in nearby houses, sometimes up to 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.
However, the most common reason some houses read higher is improper wiring and grounding connections within the house which are not wired according to the National Electrical Code (NEC). This problem is most common in older houses that have been re-wired or remodeled. Improper grounding can result in unbalanced currents which cause high AC magnetic fields, usually over a large part of the house. All the outlets and appliances usually still work fine, and the magnetic fields are invisible. If a gaussmeter shows high fields, then turning off the main breaker for the house can determine whether the high fields are coming from the house. Correcting wiring problems can be very time consuming and expensive, we offer a book and DVD to help electricians fix this problem. 
What are government limits for AC Magnetic Field exposure?  The USA has no federal legal limits for exposure to 60 Hz magnetic fields.
A few US states limit exposure living near power lines to 150 mG or 200 mG (15 or 20 uT): www.emfs.info/Related+Issues/limits/USA/   
Standards from ANSI-IEEE and WHO-ICNIRP allow even higher exposure.
Why do we recommend triple-axis gaussmeters for measuring AC magnetic fields?   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.
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.
Can the AC gaussmeters measure magnets or the Earth's magnetic field?  No, they do not measure static magnetic fields.
Magnetometers or DC Gaussmeters can measure magnets. 
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 described above and 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 (a) use an AC gaussmeter.
For (b) use the RF Cell Tower meter
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. 
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