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Re: Grounding electrodes
> From: JOlson8590 at aol_com
> Date: Thu, 12 Dec 1996 02:45:55 -0500
>
> Folks sell nice neat electrodes that are supposed to conduct any stray
> voltage directly to ground. Nice idea, but it is pretty much useless.
Methinks you do not have a clue as to the real purpose of a grounding
electrode.
> Now, why do I not believe in those neat little expensive grounding
> electrodes? Well, they just provide a path from the current to the ground.
Ah, I was right!
> If the leakage is from the other end of the tank, everything in the tank
> between the electrode and the leakage source is getting shocked.
OK, you're talking about something for which the grounding electrodes
are not designed. Let's discuss it anyway.
The situation is some appliance in the tank has a breakdown in
insulation (like a broken heater tube or a Red Devil gnawed through
the power head case) and there is a *physical* connection between a
live conductor and the tank water. And you are picturing the
equivalent of a "lighting bolt" going between the conductor and the
ground. And whatever the lighting bolt is "going through" is getting
a shock.
I have to disagree.
Consider the conditions. A live conductor with a potential of, say, 110v
is at one end of the tank. The ground probe with a potential of 0v
(hopefully) is at the other end. There will be a voltage gradient in
the water going from 110v at one end to 0 volts at the other end.
Places in between will have various potentials, 50v in the middle for
example. Also, the potential will not be a straight line thing but
will be like iron filings in a magnetic field.
Now, consider some fish exactly in the middle of the field. The
potential on one side of the fish will be a teensy bit more than 50v.
The potential on the other side of the fish will be a teensy bit less
than 50v (assuming the fish is a perfect insulator). The potential
across the fish, if anything, will be really, really small. I = E/R.
E is really, really small. R is really, really big.
Tell me again how everything in the tank between the electrode and the
leakage source is getting shocked?
> Frankly, I think grounding electrodes are a lot like those water
> softening magnets.
Well, not quite. Grounding electrodes are designed to prevent
*induced* voltages from occuring in the water. Induced voltages are
caused by EMF (generated by anything carrying AC current) interacting
with a conductor (the water in this case). The electrode holds the
water at zero potential. There are then no induced voltages. And
there is also no current flow. For there to be current flow into the
electrode, there has to be a source of electrons. There is no source
of electrons; there is no current flow.
Induced voltages are picked up by the lateral line in a fish. Fish who
aren't used to feeling induced voltages (like those from tropical
streams or oceans far away from power lines and flourescent lights)
are stressed by the unwanted effects. Stress causes disease.
Grounding electrodes have been shown to prevent AND cure diseases such
as "hole in the head" and fin rot.
But you don't have to buy them if you don't want to.
George in Colorado with A Real Fine Blizzard Happenin'