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
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
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 firstname.lastname@example.org.
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.
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:
- 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, email@example.com
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, firstname.lastname@example.org
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.
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, email@example.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.
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