Fundamentals · 6 min read

Understanding low-frequency magnetic fields

Microtesla, milligauss, exposure limits, installation limits — a short orientation for engineers and building owners entering the subject.

Units and orders of magnitude

1 µT equals 10 mG. Typical background in a home is 0.02 to 0.2 µT; directly under a high-voltage line it can exceed 10 µT; next to an LV busbar it can exceed 100 µT.

Sources

Any current produces a magnetic field. The field falls with distance, but how quickly depends on geometry: a single conductor falls with 1/r, a tight two-conductor pair with roughly 1/r².

Limits and precaution

ICNIRP reference levels for the public are 200 µT at 50 Hz. Precautionary national rules such as the Swiss ORNI are far stricter at 1 µT for installations, reflecting a preventive rather than acute-effect philosophy.

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