Power lines, electrical wiring and appliances produce low-frequency, low-energy electric and magnetic fields (EMF). EMF are invisible lines of force that exist in the area surrounding a power line or any electrical device. These fields have been the subject of much research focusing on potential long-term health effects.
This site answers some of the common questions asked about EMF.
What are electric fields?
Voltage, which causes electrical current to flow through a conductor, also causes electric fields in the air around the conductor. (A conductor is a wire that carries electricity.) Electric field strength can vary in intensity - from 3 kilovolts-per-meter in the immediate area of a transmission line (which carries electricity long distances at high voltages) to under 10 volts-per-meter for home appliances. Electric field levels inside most houses are not affected much by power lines because trees, shrubs and building materials greatly reduce the strength of electric fields (as does distance from the line).
What are magnetic fields?
Magnetic fields are only created when a current passes through a conductor. The amount of current in a transmission line varies in proportion to the changing power requirements of homes and businesses throughout the day. Therefore, the magnetic field strength also varies. Magnetic fields are created by transmission lines, home appliances - such as refrigerators, blenders, hair dryers and electric razors - and wiring when they are in use. Like electric fields, magnetic field strength decreases rapidly as the distance from the source increases. Unlike electric fields, however, power line magnetic fields can contribute to the fields found inside homes since magnetic fields are not weakened by trees or building materials.
How are EMF measured?
Electric fields are measured with a meter placed on the end of a long insulated handle (a distorted reading could be caused by a shielding effect or the surveyor’s body). Magnetic fields are usually measured by a hand-held device called a Gauss meter (magnetic fields are measured in units of Gauss). In-home magnetic field measurements can be especially difficult to interpret because there are multiple sources of magnetic fields within and surrounding the home and each source can vary greatly over time and with distance from the source. The magnetic field in homes can even depend partly on how much electricity is being used in a neighboring home.
Are there regulations for EMF?
There are no national standards or regulations specifically for power line EMF. The National Electrical Safety Code (NESC) - a national set of standards governing the installation and operation of electric and communications equipment - specifies the distance needed between power line conductors and the nearest house or building to prevent inadvertent contact. NESC is not, however, a design guide.
Can you feel EMF?
Currents produced by electric fields from household wiring or by power lines are too weak to be felt. However, some people can detect the electric field in the immediate area physically surrounding transmission lines through the vibration of hair on the head or arms. These induced currents, however, are weaker than the electrical currents which occur naturally in your body - such as the electrical activity of the brain and heart. Magnetic fields can not be sensed without special instruments.