Subject: EMF Levels due to groundwire (Pritchett)...
Date: Fri, 6 Aug 1999 125719 -0500 (CDT)
From: "Roy L. Beavers"
To: emfguru
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---------- Forwarded message ----------
Date: Fri, 6 Aug 1999 10:19:40 -0700
From: "Robert L. Pritchett"
To: "Roy L. Beavers"
Cc: joer@scm-ae.com, stanp@scm-ae.com, Tom Parkhill
Subject: EMF Levels due to groundwire
EMF-Listers;
I forwarded the note on groundwire emfs to our electrical engineers. Their
comments were;
1) Technically, EMFs do not "flow", Current does. EMFs "emanate". Remember
the "fist-and-thumb" basic electronics rule where the thumb points the
current direction and the fingers forming the fist point the direction of
the magnetic field created by the current flow.
2) Ground(Earth) wires do not or should not "carry" current. If they do, a
serious wiring interconnection exists.[understatement!] Current should be
flowing through the neutral wire. The ground is there to protect systems
from current overflows. Think of it as a radiator backwash reservoir when
the radiator on an engine gets too hot and boils over. The flush has to go
somewhere. If current on a groundwire is constant, there are some very
serious problems in the electrical system! [We call those "ground loops".]
3) All groundwires should "home" back to the electrical panel where a
groundpath should go directly to a groundrod or groundgrid. Our building
designs include a groundwire in the conduits for a "true" ground. The
groundwire is sized according to the projected amp capacity. Groundwires in
high lightening areas tend to be designed on the "heavy" side (larger
diameter, more copper) by competent electrical engineers to compensate for
oversurge activities. [Sizes in AWG are usually 12, 6, 3, or 1. 1 is huge,
12 is "housewire".]
4) Please don't cut the groundwires as advocated in an earlier post by
someone else. It's cheap insurance. Why endanger yourself? Waterpipes are
never really a good "ground". Take the time to add a true earth ground by
having groundwire installed correctly between the water heater and the
electrical panel and between the panel and "outside" to a grid or to a rod
sunk into the ground. Very dry soil/sand makes a poor ground. Wet soil
conditions around the rod works much better.
While working with the telecom upgrade at a prison in SE Washington State,
we were having groundwires installed between the telco cabinet (1st floor)
and the electrical panel in the basement. The contractor discovered that the
electrical panel ground had been tied to the steam pipe, which had been
removed when the steam upgrade project was in progress. The groundwire was
hanging in the air 20 feet over our heads. The building power was not
protected! A change order was established and the ground wire was terminated
properly between the electrical panel and the outside of the building. [Can
I get "fries" with that?]
I distributed about 40 pages of grounding and bonding information
(mini-tutorial) to the contractors and clients on that project because we
had to be set for any eventuality should a "kill fence" be installed later,
which would affect the telecommunications wiring we installed through the
campus if we didn't ground properly.
I would also check existing systems to be sure that the screws in the
electrical panels were tight where the cables terminate on the electrical
bus. They tend to come loose from heat/cold cycling over time. Aluminum
cabling is the worst for the expansion/contraction and you may actually see
arcing burns in the panel where the screws have worked loose. [not good!]
Replacement of the aluminum cabling may be your only option - long term.
There is a lot of power in those panels, so either shut them off when
working inside or let a licensed electrician do the work, for your own
safety. I know of a fellow who recently added an exhaust fan to his
bathroom, and he now proudly carries a ruined screwdriver in his pocket to
remind him of the power he found inside his electrical panel when it
"grounded out" and burned nearly through the shaft when he was careless.
Bonding wiring is the surest way of providing proper grounding over time.
Metals are fused together instead of expecting a few screws or clamps to
provide a path for the current between metals. I've seen some bizarre
terminations before using screws (ground straps screwed with el-cheapo
sheetrock screws to underfloor groundgrids!). The "fix" for bonding was
replacing the $.02 screws with $100.00 bonding kits from Erico. [see
http://www.erico.com ]
Check the electrical system in those locations you have concern. It may be
something as simple as a loose screw that needs tightening or soil that
needs wetting. And if you don't feel comfortable (heed that small voice!)
pay the professionals to do the work. They then become liable.
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Robert L. Pritchett, RCDD LAN Specialist
Telecom Designer/Engineer
SCM Consultants, Inc.
7601 W. Clearwater Ave Suite 301
Kennewick, WA 99336
Phone: 509-783-1625
FAX: 509-783-1861
Pager: 509-530-8324
http://www.scm-ae.com/robertscorner
robertp@scm-ae.com
Archive provided courtesy of WaveGuide, http://www.wave-guide.org
Reprinted with permission of Roy Beavers, http://www.emfguru.com