Can You Tell Me About Those Power Lines Behind Our House?

You may not have heard this question yet, but you will in the future. I think we should start with a primer and some basic terms related to electromagnetic fields.

Electric power generated in North America is 60 Hertz (cycles per second) Alternating Current (AC). This means both the voltage and current change polarity twice in each cycle or 120 times every second. Since the AC line frequency is between 3 – 300 Hertz, it is defined as an Extremely Low Frequency (ELF) signal.

Power Lines are characterized by CURRENT and VOLTAGE.

Electrical fields result form the strength (voltage) of the electric charge, and magnetic fields result from the option (current) of the charge. You may want to think of voltage being water in a pipe, and current as the force pushing the water through the pipe.

Electric fields are regions where an invisible line of force produced by the presence of electric charge or potential is measured. Electric fields are present whenever there is electricity. A power cord connecting an appliance to an outlet will have an electric field surrounding it, whether the appliance is on or off. (Presence of electricity is all that is needed.) Whereas a magnetic field will only be present around a cord if the appliance is turned on. (Electric current must flow.)

Electric field strength is measured in amperes per meter (A/M) and is proportional to the voltage, so high voltage lines have electric fields. Fortunately, electric fields can be shielded. Various grounding objects and materials including trees, bushes, and buildings significantly shield or reduce electric fields. When near or under high voltage transmission lines people can usually hear the crackle (corona) and sometimes sense the presence of high voltage electric fields.

Electrical current produces a magnetic field and is measured in amperes per meter (A/M). Magnetic fields are regions where invisible lines of force produced by permanent magnets and other magnetic sources are produced. High current sources such as transmission and distribution lines, motorized appliances and heater produce very high magnetic fields. Unfortunately, magnetic fields are extremely difficult to shield and easily permeate (penetrate) nearly all objects including people, buildings, and most metals. People are not able to sense the presence of high magnetic fields; however, some video display terminals will flicker when subject to high levels of magnetic fields.

Magnetic field exposure is measured with a gauss meter in units of milligauss (Mg): one-thousandth of a Gauss (G). In scientific terms Gauss (G) is the unit of magnetic flux density, which is the area permeated by magnetic fields. There are both single gauss meter has a probe that is sensitive in only one direction.

The meter is dependent on the orientation of the probe. A triple-axis gauss meter has three separate coils placed on the x, y, and z axis. This meter electronically computes the vector sum of the directional components and displays the resultant on a digital readout.