ELF magnetic field survey

Goal

Find the source of any elevated 50/60 Hz magnetic field and quantify exposure at sleeping and working positions over a full day.

Equipment

• ELF gaussmeter (power-frequency magnetic field)
• Logging EMF instrument

Procedure

1. Record meter model, axis configuration and frequency response.
2. Walk the perimeter of each room with the meter at waist height, noting every local maximum and its apparent source.
3. Measure at 0.3 m, 1 m and 3 m from each candidate source to confirm the inverse fall-off that identifies a compact source.
4. Check the service panel, meter base, and both sides of every wall that backs onto one.
5. If readings are elevated everywhere and do not fall off with distance, suspect net current on the neutral or a shared neutral, and involve an electrician.
6. Log continuously for at least 24 hours at the pillow position, sampling at least once per second where the instrument allows.
7. Report the mean, the night-time mean and the 95th percentile, not just the maximum.

Pitfalls

• Spot-reading at one time of day, when line and household loading vary by several times
• Using a single-axis meter and rotating it inconsistently
• Assuming shielding is the fix; magnetic fields pass through nearly all common materials
• Missing a wiring fault, which is the one cause that raises the whole building and cannot be solved with distance
• Using a 50/60 Hz-only meter near inverters, EV chargers or induction hobs, where the energy is in the kilohertz range

Interpret results against

• Building Biology SBM-2024 AC magnetic field bands
• WHO/IARC ELF magnetic field association threshold (0.3–0.4 µT)
• ICNIRP 2010 general public magnetic field reference level at 50/60 Hz
• Swiss installation limit value for power lines

Related records

• Electrical service panel and meter base

  The highest-current point in a building: readings in the tens of milligauss are normal within a metre, falling to background within two to three metres.

  Sources & emitters

• ELF gaussmeter (power-frequency magnetic field)

  Measures 50/60 Hz magnetic flux density in milligauss or microtesla — the instrument for wiring faults, service panels, transformers and power lines.

  Instruments

Sources

1. sbm-2024 Building Biology Evaluation Guidelines for Sleeping Areas (SBM-2024) — Institut für Baubiologie + Nachhaltigkeit (IBN), 2024. ngo, link checked 2026-08-12.
2. niehs-emf Electric and Magnetic Fields — National Institute of Environmental Health Sciences. government, link checked 2026-08-12.
3. who-elf Electromagnetic fields and public health: exposure to extremely low frequency fields — World Health Organization, 2007. government, link checked 2026-08-12.