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Magnetic fields inside a house often come from the wiring itself. Every wire carrying current makes a magnetic field, and in most homes the hot and neutral wires run together in the same cable, so their fields largely cancel. Problems begin when current takes an unexpected path. A common example is current traveling on water pipes. If the plumbing is bonded to the electrical system and something is miswired or a neutral connection is poor, part of the return current can flow through the pipes instead of the intended wiring. That current produces a magnetic field around the pipe, and the field can be steady or change with the load on the house. A wiring error, such as a neutral tied to ground in more than one place, click here a shared neutral between circuits, or a switch or receptacle wired incorrectly, can create similar stray currents and elevated fields.

A homeowner can use a gaussmeter, which measures magnetic flux density, usually in milligauss or microtesla. Read the manual first, because some meters show a single axis and must be rotated to find the highest reading, while others show a combined value. Hold the meter away from your body and from metal objects, and take readings where people actually spend time, such as beside beds, chairs and kitchen counters. Compare rooms and note whether readings change when appliances or lights are switched on or off. A reading that rises when a particular circuit is energized points toward that circuit. Readings near a panel, meter or service entry are expected to be higher and are not the same as readings at a pillow. Public documents from sources such as the World Health Organization and the National Institute of Environmental Health Sciences describe typical residential background fields and note that there is no established method of shielding a whole house cheaply. Published studies of magnetic fields and health have not produced consistent evidence of harm at ordinary household levels, but they also have not resolved every question, and scientific bodies generally call for continued research rather than reassurance.

It is time to call a licensed electrician when readings are clearly elevated in living spaces and you cannot trace them to an appliance, when a meter shows current on water or gas pipes, when you notice warm outlets, flickering lights, buzzing, a shock from a fixture, or a panel that is hot to the touch, or when you suspect a wiring error such as a neutral-ground connection. Do not open panels or move wiring yourself. Questions about billing, stray voltage on utility lines, or the service drop belong with the utility. Questions about radio-frequency exposure from wireless devices belong with the FCC. If you are worried about symptoms you connect to your home environment, that belongs with a doctor. If you face a dispute with a landlord, contractor or utility, that belongs with a lawyer.

This is covered in more detail at net current in home wiring.