Power Quality Article

Electromagnetic Fields

Question: Mike, We conducted a survey of our office space and found some elevated electromagnetic fields. Our office building is located in Washington D.C. Thus far, we found some improperly wired 3-way switches, which have been rewired and it has significantly reduced EMF levels. However, we have some areas where the field levels remain at the 12-15 mG, and our in-house electrician has been unable to determine the source of the problem.

We are trying to locate a qualified contractor that is familiar with this issue and would be able to come in an assist us in diagnosing the source of our problem, and in correcting the problem. We would appreciate any advice or recommendations you or your members could provide information on finding a book and/or firm that has experience in correcting EMF problems. It seems it is easier to find someone to measure the fields, but more difficult to find someone to diagnose and correct the problem.

Thank you for any help you may be able to provide.

Joe Descants, U.S. EPA, DESANTIS.JOE@epamail.epa.gov

Mike Holt’s Comment: Visit my site mikeholt.com/studies/emf.htm it contains valuable information as well as how to purchase an excellent book on this subject.

Response No. 1

The issue here is electromagnetic field cancellation. Around any current carrying conductor is a magnetic field. Where this electrical current is alternating, the magnetic field is also alternating. An alternating magnetic field will induce electrical currents in surrounding metal. One criterion for successfully installing an electrical circuit (in my opinion) is the cancellation of electromagnetic fields by placing the opposing-flow conductors next to each other.

For a simple receptacle circuit this is no problem. Current flows one direction in the ungrounded conductor, current flows in the opposite direction in the grounded (neutral) conductor. For lighting circuit it can get a little tricky (mistakes can easily be made). Where the power conductors come into the switchbox and are connected to the conductors going to the light it is straightforward. Where the power conductors go the lighting outlet first, we typically have what is called a 'switchleg' going down to the switch on the wall. In this circuit, there is no neutral but there is still electromagnetic field cancellation due to the opposing flow of currents.

Three-way light circuits are the problem. These circuits should be sketched out on paper with directional arrows representing current flow. The problem usually arises when a 'hot' is derived near one of the three-way switches and a neutral is derived near the other switch. In this case, we have current traveling in a path with no opposing current to cancel the magnetic fields. This is exacerbated when the conductors are run in ferromagnetic (steel) conduit. In this case, conduit heating due to circulating currents is experienced. The answer is to always derive the hot and neutral at a single location, say the first three-way switch. The neutral for the light is connected at this location. A ‘traveler’ cable, along with the return feed to the light, is fed to the other three-way switch. The return feed to the light is connected to the ungrounded conductor going to the light. So... The power feed coming in has opposing currents, the traveler-cable/light-return-feed has opposing currents, and the conductors going to the light have opposing currents.

Eric Stromberg, Senior Electrical Engineer - The Dow Chemical Company

Response No. 2

Joe, The best source of quick, clear information on EMF will likely be your local utility.

What types of "problems" are you having? The most common problem is usually interference with sensitive electronics. If this is the problem you are experiencing, it can be solved by moving the sensitive equipment away from the field or by shielding with steel. If the "problem" is personnel perception of a health link, education is the best solution - again, check with your local utility.

Magnetic fields are a function of current. As you move away from the magnetic field source, the fields fall off inversely proportionally to the distance assuming a "line" source). Possible sources are proximity to building electrical wiring, separation of phase and neutral conductors of the same circuit, and high current appliances - paper shredders will produce about 5,000mg about a foot away; can openers about 1,000mg, etc. The level of 12-15mg is not unusually high.

I am sorry that I am not available to come to help you in the near future. Perhaps you can contact Dirk A. Plummer, P.E. in New Jersey. Dirk can be contacted at dap@alum.mit.edu. Please do not hesitate to contact me if I can be of any help.

Ronald W. Quade, P.E., RWQuade@aol.com

Response No. 3

Joe, I have the following comments concerning your request.

1.     XRAY Technician Schools has a good web page on the topic: Electromagnetic Fields and Human Health.

2.     The steel tube institute and Georgia Tech offer an excellent computer program (free) for modeling EMF sources: Georgia Tech offers a course in on this subject call 404-385-3501 for more info. The name of the course is: "Grounding, Harmonics, & Electromagnetic Influence Design Practices". I plan to attend. While the course is not about EMF, it does cover a number of causes of EMF problems.

Mike Holt’s Comment: I have attended the program, it is excellent, and the free software is great.

Some other helps include:


http://www.epri.com/ - Search for “EMF”

Generally 12-15 mG is normal and is generated by everything electronic including lamps, monitors etc and are beyond finding solutions for. If there is a single piece of equipment that is a cause or is particularly sensitive to that level of EMF then some things can be done.

If there is a cable in the floor or wall that is the source, then it should be put in steel conduit. If it is in a floor or wall (like in a strip mall, under the floor) then the solution is to rearrange the office/equipment that might be bothered, to a lower EMF area. A plate of steel (only iron, cobalt and nickel will work, other metals are useless for shielding EMF) between the source and the sensitive equipment will redirect the magnetic field and eliminate a problem for spot problems. Most solutions like this are too expensive to implement on a large-scale basis.

The problem could be caused by neutral current flowing through metallic conduit (conduit being used as a current-carrying conductor). This could be caused by incorrect outlet or equipment wiring or a neutral-to-ground bond at a subpanel. Both of these are code violations and can be dangerous if extreme.

If a monitor has a bad case of the jitters then you can move it, replace it, or buy an EMF shield for it (expensive and obtrusive). If you have questions that I can help with, please call or Email me.

Brian E. Purvis, PE Senior Engineer, brian.purvis@ieee.org

Response No. 4

In response to the question regarding high output EMF. I would suggest checking to insure that paralleled power runs have all phases in the same conduit of each parallel run. Most of these types of problems take a good deal of hands on footwork to correct.

Sincerely, Jack Edwards Master Electrician

Response No. 5

Seems to me that an Electrical Engineer specializing in Power Quality would be the best authority to analyze and solve this or other PQ problems. They have the training and experience to go beyond what electrical contractors can do.

Cordially, Fredrick Rea O'Keefe, fredrick@tech-center.com

Response No. 6

A conduit system cancels out EMF because the pipe totally encircles the wire. Nonferrous metal (aluminum) and nonmetallic raceways do not cancel out the EMF.

Response No. 7

Hello Mike, I teach a seminar to show you how to find the wiring errors that cause high EMF levels. See my web site at www.angelfire.com/pa3/emf Electromagnetic Field (EMF) Thanks, Ed Chavern, chavernet@aol.com

Mike Holt’s Comment: I do not know this person, nor do I know if he is qualified to teach on this subject. If anybody has any feedback, I would like to know.

Response No. 8

Radio towers, cell phone towers, 2 way radios, CB's or any type of communication stations that produce high output waveforms can disrupt and create interference.

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