1. While technically correct I didn't get into this in the interest of simplicity. A worst case value for for the resistance of a wet human body is 300 ohms. The resistance of a grounding plug is around o.1 ohms. This means almost 3000 times more current will flow through the ground probe during a fault than through a person. On a 20 amp breaker that limits continuous current through a person .006 amps in a worst case scenario. Most people wouldn't even get a tingle at that level.
2. Salt water is not a dielectric. By definition, a dielectric is a poor conductor of electricity. Salt water is an excellent conductor of electricity. I suggest you google a Leyden jar to learn more. In a salt water capacitor, the salt water is not the dielectric. Typically, the plastic or glass of the bottle is the dielectric. The water works to aid conductivity with the inner electrode.
3. Kirchhoff's law is always relevant. The sum of electrical voltages in a closed loop always adds to zero. With the low resistance to ground you can use this law to show exactly how much current you would need across the ground probe to achieve any dangerous level of voltage in your tank, regardless of possible parallel paths. It is much more current than your house can supply for more than an instant.
4. Just because a lineman can't hang a ground on every section of the conductor he is working on doesn't mean that it is worthless to hang grounds at all. We may not be able to "work between grounds" in a salt water tank but it is much better to have 1 ground than none.
5. A ground probe doesn't stop induction any more than a floor stops gravity. What a ground probe does is reduce the voltage in a tank to a safe level for the fish (induced voltages on a 120V system are not dangerous to people). I maintain an old Simpson voltmeter just because of this principle. Modern voltmeters are very high impedance devices. If you remove the power source to a device in an industrial setting it is very common for it to still read over 200VAC for a 480V system due to inductance. If you use an older Simpson voltmeter, it has a much lower impedance and will drain that voltage to ground if it is induced. If the voltage stays steady you know you didn't isolate the power correctly. In my tank, with the grounding probe removed, I see between 23V-27V. With the grounding probe installed, my voltage drops to under 400mV. My ground probe draws around 0.2 amps to accomplish this.
A grounding probe is very useful, and the circuit breaker(s) you feed your aquarium with is a fault clearing mechanism. Using it in conjunction with a GFCI is even better.
In the trade, a single ground connection on a conductor is a very common practice. I have already established that salt water is not a dielectric (insulator). Single point grounds are most certainly considered life saving practices.
1. Unfortunately, sometimes in the interest of simplicity we miss some important nuances. While the grounding probe itself may measure 0.1 ohms across it's length, you may have a significant amount of saltwater between the voltage injection point, and the grounding point. If the ground probe is in my display tank for example, and my return pump is defective, and I reach into the sump, your simplified current calcs fall apart. Also, how many cycles does it take for a 20 amp breaker to trip, and how much current will a 20 amp breaker allow to flow in a fault condition before it trips? I'm sure you are aware fault currents can far exceed the protection continuous rating, and is somewhat irrelevant to the discussion, suffice to say they can be lethal with or without a grounding probe.
2. If we want to get into specific definitions then, saltwater is not an "excellent conductor of electricity", as far as conductors go, it's a rather poor one. Nor is it a particularly good insulator, in fact its properties are very close to the dividing line between the two. Perhaps some of the confusion lies in a misunderstanding of exactly how salt water "conducts" electricity. It doesn't work like a typical solid conductor pushing electrons (or holes) down the line, which is what most of your statements seem to be based on. Current is carried by free ions in the electrolytic solution (salt water), which is part of the reason why basic ohms law, kirchoff's current and voltage laws essentially break down, and are no longer "laws" applicable to what is happening when electrical potentials are applied to electrolyte solutions. 2(a) A Leyden jar is similar in construction to a salt water capacitor, but is not, as it can be constructed without salt water
In a salt water capacitor, the dielectric medium includes both an electrolyte (salt water) + the jar wall. Ions in the solution move to the opposite charged electrode and become a double layer...it becomes much more effective at shielding the charge, and charge densities will be much higher.
3. Kirchoff's law(s) are not "always relevant", they are *only* relevant in, and wholly dependent on the lumped element model. Kirchoff's laws are a very simplified method to describe simple closed circuits models with the electric charge remaining constant. KCL is dependant on the assumption that current flows only in conductors, and that it immediately flows out the other end. Since salt water conducts by free ions and there are an infinite number and varying paths and charge densities, the lumped element model is not applicable, therefore the laws do not apply.
4. Lineman use EPZ (EquiPotential Zero..or grounding). This involves a far more complicated grounding scheme than a probe in a tank of electrolyte. If you want to put a ground grid in the bottom and sides of your tank, tie that to a potential equalizing mat for you to stand on, wear dielectric boots and class 0 gloves while working on your tank, after you have isolated the power to the tank, you can compare the two, otherwise there is zero comparison between the two methods. You realize the main reasons linesman hang grounds is to force the protections to work much faster should the line become energized, and to drain induced voltages that may be present and dangerous in the kV levels. It's their insulated equipment that protects them from being zapped, not the grounds.
5. Sure, a ground probe can drain some induced voltages in the tank, and as you said, induced voltages off a 120v system isn't really a concern.
Grounding is a complex topic on which experts in the field don't agree. Look at entire committees which are unable to come to agreements for codes and standards for grounding, or go on any forum discussing high voltage work, and watch guys who have been hanging grounds on high voltage systems for more than 30 years argue about practices and the like. We are never, ever, going to come to a consensus on a reef tank forum, and I knew that when I debated on responding to the thread. I responded only so that through discussion, people would realize that adding a ground probe to the tank can give a false sense of security that isn't there. I will agree, that on the whole, a grounding probe may add some safety in some situations. To rely on it with your life is foolhardy.
I would like to leave the participants of this thread with this, especially those that think I am wrong in my assessment of the safety afforded by a grounding probe;
Most codes require some sort of ground fault interrupter in bathrooms, pools, hot tubs etc.
If a grounding probe in an electrolytic solution ("un-pure" water such as in our tanks, our swimming pools, hot tubs, baths, etc) provided any real measure of life safety, it would be written into every electrical code as required equipment where people immerse body parts.
There are exactly Zero codes that I am aware of, that require a grounding probe in the water. Why is that?
