Magnetic Fields – EMF Consulting

When performing EMF surveys many “EMF consultants” only evaluate low-frequency magnetic fields.  When folks call and say they “have an EMF meter” and are measuring “high emf,” they generally have a Gauss meter and are measuring magnetic field field strength or magnetic flux. Most Building Biologists focus on Alternating Current (AC) electromagnetic fields, and in addition to magnetic fields we like to evaluate low-frequency electric fields, “dirty electricity,” and radio frequency radiation. This blog focuses on magnetic fields – EMF consulting.

Most certified Building Biology Environmental Consultants focus on AC EMF which has been created by humans. Every bandwidth between the two green arrows has been filled up with human-generated EMF and EMR.

Human Created EMF Spectrum

What are Low-Frequency Magnetic Fields?

Magnetic fields occur wherever there is current flow, or Amperage. Magnetic fields emanate from a source in more-or-less concentric rings. I like to think of magnetic fields as donuts!

Magnetic Fields from Power Line

So whenever there is amperage (current flow) magnetic fields are created. They emanate from the conductor in a predictable manner. Current, like water, takes the path of least resistance through buildings and neighborhoods. So sometimes we may inadvertently have current flowing on our plumbing systems, phone or cable utilities, or electrical grounding system. An amazing fact of EMF physics is that magnetic fields can “cancel themselves out.”  Modern day 3-wire or 4-wire cabling has lead to reduced ambient magnetic fields because the Hots and Neutrals are so close together the magnetic fields mostly cancel themselves out and cannot be measured far from the electrical cable. Buildings with active Knob-and-Tube wiring generally have higher ambient magnetic fields because of the distance between the Hot and Neutral of each circuit. This is only true when there is a load on the circuit.

Magnetic Field Cancellation in Balanced Load Circuits

A known variable is always distance. Magnetic fields decrease in field strength with distance from the source. Oddly, the rate of reduction with distance is not constant from different types of sources. For instance, magnetic fields from a coil-type source, such as a motor or transformer, drop off exponentially at a cube of the distance (1/r3), but mag-fields from an unbalanced line source drop off proportionately with distance (1/r1). Therefore wiring errors and “stray current” sources can be much more influential than electrical system point sources in our buildings.

AC Magnetic Field Drop-Off Rates

Magnetic fields are measured in Tesla or Gauss, and because those units are so large we drop down to the billionth of a Tesla [nanoTesla (nT)] or thousandth of a Gauss [milliGauss (mG)] to be able to measure everyday exposures around homes and offices.

There can be very high and wide-spread magnetic fields whenever there is a wiring error or stray current on an electrical line, plumbing system, data cable, or any other metallic conductor in a building. People call all the time for EMF inspections because they are considering buying a home near a power line, or an office suite is right next to a large electrical conductor. But, statistically speaking, proximity to these known point sources is often less of a concern than internal wiring errors. This is generally considered good news because internal wiring errors can be fixed, but distance from external sources is beyond owner control. So if you’re concerned at all about EMF we suggest having an EMF assessment performed – even if you’re not near any mega external sources.

4.7 milliGauss near Knob-and-Tube Wiring

 What levels of EMF – Magnetic Fields are safe?

We are environmental scientists and industrial hygienists – not doctors or public health experts. So we make it a point to avoid saying what levels of magnetic fields “are safe.” However, since we believe in the precautionary principle we align ourselves with those pushing for more stringent regulation of EMF, and we most often refer to the more conservative recommended exposure levels from the BioInitiative Report (< 1 mG, or < 100 nT) or the Austrian Medical Association and Building Biology (< 0.2 mG, or < 20 nT). These levels are well below those established by our regulatory agencies in the US, and these levels can be difficult to achieve in some buildings near high-voltage transmission lines or in multi-tenant buildings with wiring errors and stray current problems.

Common Point Sources for Magnetic Fields

Magnetic fields are present wherever there is current flow, but some sources are more notorious than others.

Common External Sources of Magnetic Fields:

• High-voltage power lines (large amount of amperage and large distance between Hot and Neutral conductors)
• Transformers (large amount of current and mega coiling)
• Utility substations (obvious reasons)
• Good blog outlining EMF Rules of Thumb for avoiding this sort of external source

Common Internal Sources of Magnetic Fields:

• Bedside clock radios
• Lighting or other low-voltage transformers
• Wiring errors and stray current loops
• Knob-and-Tube wiring
• TVs and other electronics
• Motors and pumps
• Good blog outlining EMF Best Practices for avoiding these internal sources

Magnetic fields – EMF consulting

There is much advice we can offer about reducing exposure to magnetic fields. While helping clients plan for a remodel or design a new structure, the following principals are what we constantly refer to:

1. Site selection can be key. If you’re near a large external source it might be impossible to achieve 0.2 milliGauss throughout a structure.
2. Distance, distance, distance. The electrical drop-down, wiring layout, and electrical panel locations should be isolated from high-use areas.
3. Proper wiring of panels is easy – as long as the electrician understands the principals of low-EMF wiring.
4. Proper building wiring ensures there are no Neutral-to-Neutral or Neutral-to-Ground. During magnetic field EMF consulting we identify these problems all the time!
5. Shielding is a last resort. There are some “magnetic field shielding materials” that might reduce ambient levels by 1/3 to 2/3, but I’ve never seen shielding completely eliminate a magnetic field.

For some of the knowledge and images above, we extend great appreciation to Karl Riley and his book Tracing EMFs in Building Wiring and Grounding and the not-for-profit Institute for Building Biology & Ecology.