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power line magnetic fields lines and the wiring in your home carry alternating current, and that current produces an alternating magnetic field at 60 Hz, the standard frequency in the United States. These fields are a normal byproduct of moving electricity. They are strongest close to the source and fall off quickly with distance, which is why the field a few inches from a panel or a cord can be much larger than the field a few feet away. Unlike radio waves, these fields are not radiation in the sense of energy traveling through space; they are the magnetic part of the near field around conductors, and they drop steeply as you move away.

Exposure is commonly reported in milligauss in the United States and in microtesla in much of the scientific literature. One microtesla equals 10 milligauss, so 1 milligauss is 0.1 microtesla. A reading of 2 milligauss is 0.2 microtesla, and 10 milligauss is 1 microtesla. The two units describe the same thing, and published studies and public documents often use one or the other, which can make comparisons confusing until you convert.

Typical background levels in homes away from appliances and wiring are usually small, often around or below a milligauss, though this varies with the building and the neighborhood. Near appliances, motors, and wiring, readings can be higher. Outdoors near distribution lines, fields depend on current, distance, and how the conductors are arranged, and they generally fall to low levels within tens of feet, though this too varies. These are general descriptions, not fixed numbers you can rely on for a particular location.

Public exposure limits differ by country and by the body setting them. In the United States there is no single nationwide standard for 60 Hz magnetic fields from power lines or household wiring. Some states and local jurisdictions have addressed transmission line fields in siting processes, and some public health and engineering organizations have published guidance. Internationally, the International Commission on Non-Ionizing Radiation Protection has published reference levels for public exposure, and other bodies have issued their own recommendations. These limits are set well above ordinary residential levels and are intended to avoid established effects, not to draw a sharp line between safe and unsafe at low levels.

On health, the published evidence is mixed and has been reviewed repeatedly. Some epidemiological studies have reported associations between long-term exposure to relatively high residential magnetic fields and childhood leukemia, while other studies have not, and laboratory work has not established a mechanism. Reviews by public health agencies have generally described the evidence as limited and have not concluded that typical residential fields cause disease. That is not the same as proving there is no effect, and it is not a reason for alarm about ordinary exposure. If you have a specific health concern, that question belongs with a doctor. If you have a dispute over a power line or a property, consult a lawyer. For measurements or complaints about utility equipment, contact the utility. For questions about radiofrequency devices and their regulation, the Federal Communications Commission is the relevant agency. Devices marketed as shields or stickers that claim to block magnetic fields or protect health are not a substitute for distance, which is the practical way fields fall off.

For more on this, see power line magnetic fields.