WHAT ELECTRICIANS SHOULD KNOW ABOUT EMF
By: This Article by Karl Riley email@example.com/
who wrote the book.
Tracing EMFs in Building Wiring and Grounding.
The health concern which developed from research connecting
childhood leukemia and brain tumors to nearby power lines lead to some
unexpected findings about building wiring. When EMF consultants were called
in to take magnetic field measurements in buildings it turned out that
the wiring itself often produced higher magnetic field levels than nearby
power lines. Further investigation showed that these elevated fields were
not due to correct wiring but were caused by certain wiring errors - violations
of NEC - which are seen all too often.
To backtrack: some readers may be wondering if there
is anything to this health concern, particularly when there have been reports
in the media that there is nothing to it. It should be understood that
the financial concern with the outcome of this research makes the cigarette
company's worries seem insignificant. When billions of dollars of retrofits
are at stake, you are going to have "controversy". For the most
authoritative review of the research yet conducted you can download the
document from the internet. It is the NCRP report at http://www.microwavenews.com/ncrpl.html/
For a book written for the layman I recommend Electromagnetic Fields by
Blake Levitt, Harcourt Brace Harvest Books, 1995, a paperback that sells
Recording Elevated Fields
But back to building wiring. As an EMF measurement consultant
my job is to take magnetic field measurements at regular intervals throughout
the building, record these measurements on a floor plan, and look for unusual
field levels. The measurement unit used in the U. S. is milligauss (mG).
The test instrument is called a gaussmeter. A correctly wired building
that is not near a power line will usually show either 0.0 mG or a few
tenths in most of the occupied areas of the building. The few tenths are
usually due to fluorescent light ballasts, unless electronic ballasts have
been installed, in which case you won't see anything on the meter. If there
are wiring errors you will see milligauss measurements up to double digit
readings in areas of rooms where the circuits run.
Identifying EMF Source (NEC Code Violations)
Once elevated field levels are recorded the second step
is to identify the source. Appliance sources are very local and the fields
weaken quickly. Power line sources can be identified easily by their presence
in all areas and by the fact that they continue outside the building and
get stronger nearer the power line. The most common sources, in my experience,
are miswired circuits as well as fields due to grounded neutral current
on water pipes, gas pipes, etc. What kind of miswirings am I talking about?
Most commonly violations of NEC sections 300-3(b) and 310-4, which require,
respectively, that all conductors of a circuit must run together, including
the neutrals and equipment grounding conductors; and, that paralleled conductors
are not allowed in conductors smaller than 1/0. A second type of error
is addressed in 250-23(a) and 250-61(b) which prohibit connecting neutrals
to ground on the load side of the service entrance.
To identify the circuits involved I go to the breaker
boxes and use clamp-on ammeters to find the circuits carrying "net
current". Net current means the portion of current not canceled out
by an equal and opposing current in the circuit. Correctly wired circuits
have zero net current, which means that if you clamp an ammeter around
the circuit it will read zero. If there is net current the ammeter will
read it and you will have found one circuit giving out a strong magnetic
field. For a complete description of the whole process of measurement and
source identification refer to my book, Tracing EMFs in Building Wiring
After the circuits have been identified and found to
have either a deficit or an excess of neutral current, other tracing techniques
are used to follow the circuit out to find the junction box where the error
was made. Typically this is the kind of error we find: sometimes at the
end of the run of two branch circuits, the circuits share a junction box.
One may feed, say, some outside lights. The other load served through the
junction box may be, say, bedroom lights. One load is fed by one branch
circuit; the other is fed by the other branch circuit. The hot conductors
are wire nutted to their respective circuits, but when it comes to the
neutrals, sometimes they are all twisted together with one big wire nut.
What does this do? Suppose the bedroom lights are on. The neutral return
current, since it is joined with the neutrals of both branch circuits,
splits and returns to the panel through both neutrals. This creates two
net currents: one by robbing the bedroom circuit of some of its balancing
neutral current and the second by putting neutral current on the outdoor
light circuit, which gives off an equal magnetic field.
Connecting neutrals in this way creates a parallel path
and violates 310-4. Also, it makes the second neutral a part of the first
circuit, but since the second neutral runs in another path, there is a
violation of 300-3(b). Why does Code prohibit these net-current producing
connections? Because it increases the impedance of the circuit and may
lead to inductive heating, particularly if the circuits run in metal conduits
or metal clad cable. Also the magnetic fields produced often cause problems
in electronic equipment. Computer monitors will start to flicker at anywhere
from 5-15 mG; usually around 12 mG. "Smart wiring" is sensitive
to these net current fields since the small signals induced may be enough
to give spurious commands to the system. If magnetic fields are eventually
proven to be co-promoters for some cancers and Alzheimer's, the liability
of electricians creating these fields will get the attention of the lawyers
who are at present suing power companies.
Connecting neutral to ground on the load side of the
service entrance will cause similar net currents, but this time one of
the net currents is on the circuit and the twin current is on a water pipe,
sprinkler pipe, gas pipe, building steel, etc. This condition is caused
when an electrician does not isolate the neutral as he should in a subpanel.
There are other ways of misconnecting neutral to ground which I go into
in Tracing EMFs.
Normally an electrical inspector will not detect these
errors since his protocol does not include looking in junction boxes. Of
course he should see grounded neutral busses in subpanels, but even there
it may not be obvious and he may miss it. But anyone including a home owner
can walk through the building with an inexpensive gaussmeter and immediately
see that something is wrong (providing the lights are on). Eventually gaussmeters
will be used routinely when inspecting buildings for sale, and by school
officials and environmental consultants. These wiring errors will show
up clearly. It would be very prudent for any electrician reading this article
to think over his practices as well as the practices of the men he may
hire to run the wiring and make sure that neutrals are correctly connected.
Incorrectly wired 3-way switches also will produce high magnetic fields.
Use 3-wire travelers and don't try to get away with 2-wire (only switch
legs can be 2-wire).
Magnetic fields due to net currents on grounded water
pipes and consequently service drops are in a second category, since they
are not due to wiring error. However the Code does address this situation
in 250-21. Objectionable Current over Grounding Conductors. I refer the
interested reader to my book for a thorough discussion of this problem
and what can be done about it for a concerned client. This article is only
meant to bring this new set of power quality concerns to the attention
of electricians and contractors.
To order the book click here.