# 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.

- Canonical URL: https://emfbase.com/emitters/pad-mount-transformer
- Collection: Sources & emitters
- Record id: `emitters:pad-mount-transformer`
- Status: verified
- Last verified: 2026-08-12
- JSON: https://emfbase.com/api/emitters/pad-mount-transformer
- Also known as: distribution transformer, green box transformer

## Key values

- **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 mG — Measured range — Typical range at 1 m from the enclosure under normal load. [niehs-emf]
- **3 m:** 1–10 mG — Measured range — Typical range at 3 m. [niehs-emf]
- **5 m:** 0.2–3 mG — Measured range — Usually background by 5 m. [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](https://emfbase.com/emitters/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

- `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

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.