# 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.

- Canonical URL: https://emfbase.com/emitters/high-voltage-transmission-line
- Collection: Sources & emitters
- Record id: `emitters:transmission-line`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/emitters/high-voltage-transmission-line
- Also known as: power line, overhead line, pylon, HV line

## Key values

- **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 mG — Measured range — Directly beneath the conductors at mid-span, dependent on current, conductor height and phase arrangement. [niehs-emf]
- **30 m:** 1–10 mG — Measured range — Typical range at 30 m from the centreline. [niehs-emf]
- **60 m:** 0.2–3 mG — Measured range — Approaching residential background at 60 m for typical loadings. [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](https://emfbase.com/limits/swiss-installation-limit-power-lines): 1 µT (10 mG) magnetic flux density at places of sensitive use — the strictest power-frequency installation value in force in Europe.
- [WHO/IARC ELF magnetic field association threshold (0.3–0.4 µT)](https://emfbase.com/limits/who-elf-0-3-0-4-microtesla-association): 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.
- [IARC classification of ELF magnetic fields as Group 2B (2002)](https://emfbase.com/studies/iarc-2002-elf-magnetic-group-2b): 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.

## Sources

- `niehs-emf` National Institute of Environmental Health Sciences. *Electric and Magnetic Fields*. https://www.niehs.nih.gov/health/topics/agents/emf — government, link checked 2026-08-12
- `who-elf` World Health Organization (2007). *Electromagnetic fields and public health: exposure to extremely low frequency fields*. https://www.who.int/teams/environment-climate-change-and-health/radiation-and-health/non-ionizing/exposure — government, link checked 2026-08-12
- `ch-onir` Swiss Confederation (2000). *Ordinance relating to Protection from Non-Ionising Radiation (ONIR / NISV, SR 814.710)*. https://www.fedlex.admin.ch/eli/cc/2000/38/en — regulation, link checked 2026-08-12

Data licence: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Dataset version 2026.08.1. Retrieved from EMFBase, https://emfbase.com.

This record is reference data, not medical or legal advice. Regulatory limits, scientific guidelines and precautionary values are labelled separately and answer different questions.