graze-l May 2006: [SPAM] - Re: [Graze-l] [SPAM] - Why
insulated grounding wire? - Found word(s) barn in the Text body - Email found
in subject - Found word(s) barn in the subject - Email found in
subject
Hi Charles,
Stray voltage is not easy to detect, even for professional engineers
working on this problem. We have several in our state who work with
government and power companies to try and determine the cause. Even
measuring mV (millivolts or 1/1000th of a volt) is not always going to
help you. Some of these transients are fleeting and can come from miles
away from factories, businesses and schools with inductive loads and
square wave generation. The former mostly from large motors and the
latter from the new technologies (T-8 lighting with electronic ballasts,
VFD's (Variable Frequency Drives) such as you find on AHU's (Air
Handling Units), computer and video equipment that tend to use
switching power supplies. Some of the high harmonic energy (multiples
of 60 Hz) have a difficult time traveling back to the sub station with
older designed power distribution systems and an increasing amount of
return energy can be over the earth. This is currently very
controversial and it is not always easy to separate fact from fiction.
One way to accurately measure stray voltage is to use a storage
oscilloscope which can hold the waveform with its attendent voltage and
rise and fall times. This can give you some indication of the source.
This type of equipment is very expensive and only a few troubleshooters
seem to have it. If the leakage is constant, you could then measure the
voltage with low cost equipment since most DVM's (Digital Volt Meters)
can see a few millivolts on their most sensitive settings. The other
issue is what do you measure across? The standard approach is to measure
between a cow drinking location and a point where the hind feet would be
and measure this across a 500 ohm resistor to simulate a livestock
equivalent. They usually use some hydraulic pressure on the floor probe
to match the weight of the livestock. The state folks claim that you
would need over a 0.5 volt differential to be of concern.
For graziers with cattle outside drinking from a tank, you should be
able to detect this kind of a voltage gradient if it is a constant leakage.
Sincerely,
Rick W.
Charles Ritch wrote:
> Rick,
>
> You wrote: This can help to reduce any chance of stray voltage.
>
> How would one check for "stray voltage". I am told the standard
volts
> meters, ever thought they measure in mV, are not accurate for
> measuring stray voltage. I call my electrical supply house and they
> wanted over $700 for a meter that could accurately measure mV.
>
> Thanks,
>
> Charles Ritch
> Goose Pond Farm
> ritch@hiwaay.net
