Pad-mounted or pole-mounted distribution transformer
A local transformer produces a strong but rapidly decaying magnetic field: often tens of milligauss at a metre, at or near background by five metres.
elf magneticoutdoorhome
Last verified 12 August 2026.
Also searched as: distribution transformer, green box transformer
- Category
- elf magnetic
- Emission bands
- Power frequency and harmonics
- Environments
- outdoor, home
- Duty cycle
- Continuous, proportional to the load of the served customers.
Field strength by distance
- 1 m
- 5–50 mGMeasured range — Typical range at 1 m from the enclosure under normal load.sources: niehs-emf
- 3 m
- 1–10 mGMeasured range — Typical range at 3 m.sources: niehs-emf
- 5 m
- 0.2–3 mGMeasured range — Usually background by 5 m.sources: niehs-emf
Mitigations, most effective first
- Keep habitable rooms and outdoor seating more than 5 m from the unit where site layout allows.
- Transformer fields decay faster than transmission-line fields because the source is compact.
- If readings do not fall with distance, look for the secondary service conductors rather than the transformer.
- Unbalanced service conductors, not the transformer core, are the usual cause of persistent elevated readings.
Measure with
- ELF gaussmeter (power-frequency magnetic field)
Related records
- 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.
Sources & emitters
Sources
- niehs-emf Electric and Magnetic Fields — National Institute of Environmental Health Sciences. government, link checked 2026-08-12.
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