Folks,
The fact is that stray voltage can be very, very, difficult to solve,
particularly on dairy farms. In some cases, the farms went out of
business. Some will say that it was not stray voltage, and that is
possible. (But I personally know of several families who are no longer
dairying and in some cases nearly lost everything, so it is not a
theoretical thing with me). Because of my work with environmental
safety and health issues, I cross paths with those who believe that it
is not stray voltage as such, but what they consider "power quality"
issues. I tend to be in the middle on this issue since it has not been
scientifically proven and it has brought in an cult like belief with
strong emotional views rather than hard science. However, this does not
necessarily mean that this problem does not exist.
The grounds here in the U.S. are typically required to be copper clad
5/8" rods that are 8 foot long and with a maximum 25 ohm contact to the
earth. Farms are different than homes due to the separation of
buildings. This means that you can have separate grounds at each
building's service entrance and you can have a potential difference
between buildings. The very first thing investigators do is to insure
that the ground is within spec.
If you have a constant leakage current of some kind, it is fairly easy
to measure this stray voltage with conventional metering.
But no matter how well you design your ground, if you have transients
coming via the earth from outside sources, you can have difficulties.
For example, one electrician who specializes on solving these kinds of
problems has told me that he has witnessed dairy cows exhibiting severe
responses to transient voltages that were present, even though the farm
was told that previous tests showed no stray voltage. He would watch the
livestock react to each transient on a consistent basis.
In these cases, it is not adequate to use a conventional meter ... DMM
(Digital Multimeter) or analog meter ... which have much too slow of a
response to transients. You have to at least use an oscilloscope and
even better a storage oscilloscope that holds the waveform on screen so
you can better identify the signature. This can help to ID the source of
the problem.
There have been alleged cases where defective equipment (hot water
heaters) one neighboring farms were causing problems on a farm one mile
or more away. So even though you may have your farm's grounding system
completely within specifications, you could still have a problem.
Sincerely,
Rick W.
