High-voltage transmission line
Fields directly beneath a loaded transmission line reach tens of milligauss and fall off roughly with distance for a balanced three-phase circuit, reaching background at 30–60 m for typical loadings.
Last verified 12 August 2026.
Also searched as: power line, overhead line, pylon, HV line
- Category
- elf magnetic
- Emission bands
- Power frequency
- Environments
- outdoor, home
- Duty cycle
- Continuous, proportional to circuit loading, which varies through the day and season.
Field strength by distance
- at the source
- 10–100 mGMeasured range — Directly beneath the conductors at mid-span, dependent on current, conductor height and phase arrangement.sources: niehs-emf
- 30 m
- 1–10 mGMeasured range — Typical range at 30 m from the centreline.sources: niehs-emf
- 60 m
- 0.2–3 mGMeasured range — Approaching residential background at 60 m for typical loadings.sources: niehs-emf
Mitigations, most effective first
- Measure over 24 hours at the property line and inside the building, since line loading varies.
- A single daytime reading can understate or overstate the annual average by several times.
- Compare the annual average against the Swiss 1 µT installation value and the Dutch 0.4 µT policy target for new lines.
- Gives a defensible frame of reference; no regulatory limit anywhere is close to typical residential exposure.
- Treat magnetic shielding as a last resort; it requires high-permeability alloy and rarely gives more than 50% reduction in a residential retrofit.
- Sets expectations correctly — distance and source correction are the only reliable options.
Measure with
- ELF gaussmeter (power-frequency magnetic field)
- Logging EMF instrument
Related records
- Swiss installation limit value for power lines
1 µT (10 mG) magnetic flux density at places of sensitive use — the strictest power-frequency installation value in force in Europe.
Exposure limits
- WHO/IARC ELF magnetic field association threshold (0.3–0.4 µT)
The average daily exposure level above which pooled epidemiological studies report an association with childhood leukaemia, and the basis for the IARC Group 2B classification of ELF magnetic fields.
Exposure limits
- IARC classification of ELF magnetic fields as Group 2B (2002)
IARC classified extremely low frequency magnetic fields as possibly carcinogenic to humans (Group 2B) on the basis of consistent epidemiological associations with childhood leukaemia above roughly 0.3–0.4 µT.
Research record
Sources
- niehs-emf Electric and Magnetic Fields — National Institute of Environmental Health Sciences. government, link checked 2026-08-12.
- who-elf Electromagnetic fields and public health: exposure to extremely low frequency fields — World Health Organization, 2007. government, link checked 2026-08-12.
- ch-onir Ordinance relating to Protection from Non-Ionising Radiation (ONIR / NISV, SR 814.710) — Swiss Confederation, 2000. regulation, link checked 2026-08-12.
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