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More Breaker Panel Mess
Larry, I think your conclusions are based on some incorrect assumptions
regarding the path resistances through earth and water. The beginning point of disagreement may be your assertion that seawater is a great conductor. Compared to copper, seawater is a terrible conductor: orders of magnitude worse, in fact. I admit it is not easy to do actual calculations on the resistance of a particular seawater path using specific electrodes, since path resistance will depend on surface areas of the electrodes and the distance between them, in addition to the resistivity or conductivity of the seawater. But the concept should be clear. At 120 volts, a 50 ampere circuit would require a path resistance of 2.4 ohms. There is no way you can find a six foot path from your prop to the earth below back to the ground/neutral AC connection point with a resistance of 2.4 ohms. Even if the water path resistance were zero ohms, (which would be low by some orders of magnitude) the earth itself will constitute more than 2.4 ohms resistance. I would not advise you to do this with 120 volts, but with a 6 volt transformer, connect one side to your prop and the other side to your green AC grounding conductor and measure the current and calculate the resistance of the path. The path will be from the transformer to your prop through the water to the earth through the earth to the ground/neutral connection point and then back to your transformer through the green grounding conductor. Tell us what you find. So even if the path resistance through the water from your prop to the prop in the next slip is an order of magnitude greater (quite unlikely) than the path resistance from his prop back through the earth to the ground/neutral connection point, there will still be a voltage between your prop and green grounding wire on your boat (which has negligible resistance back to the ground/neutral connection point). It is quite possible that the path through your prop and green grounding wire will have lower resistance than the path from the neighbor's prop through the water and the earth. Bottom line: what you have is an AC voltage connected to two parallel resistances. But the key point is that these resistances are sufficiently high that when a human body's resistance is added in parallel with them, enough current will flow through the body to cause electrocution. FWIW, I think you are attempting to apply electrostatics principles to this situation. It is quite true that if you have an object with a net positive or negative charge and touch it to earth (or water) that net charge will dissipate through the earth (or water). That simply doesn't happen here. If you apply a voltage to two electrodes stuck in the earth (or the water) you will find that depending on the parameters mentioned above, a finite resistance is encountered. Place the human body's resistance in parallel with that resistance and some current will flow through the body. Not telling you a thing here, Larry, just that the issue is really the magnitudes of the path resistances involved. Even at RF, seawater does not offer anything close to a zero ground loss resistance. Depending on a lot of things, some radial systems on earth are actually far better largely because of water's relatively lower conductivity. The confusion over the properties of seawater at RF arises from the fact that refelctions from seawater are far superior to reflections from any known earth types and this superiority is sometimes incorrectly transferred to seawater's performance as a ground plane. But that's for a different time. Regards, Chuck Larry wrote: chuck wrote in news:hAskf.8744$N45.1460 @newsread1.news.atl.earthlink.net: Next, you grab your engine with one hand and open the door of your fridge with the other as you reach for a cold one and you receive an unhealthy dose of 60 Hz. Wow...this scenario is pretty absurd, as I suspected, but I'll respond to these unlikely events, anyways. Point...there is NO PATH from your neighbor's boat prop to your boat prop as the water between the boats IS EARTH GROUND....seawater to earth, a great ground, even if it's a freshwater lake. The path from the neighbor's absurd boat, taking the least resistance, is from the boat into the conductive water to EARTH GROUND, back to the AC source. There is absolutely no path to you and your absurd fridge. Don't believe me, take ahold of the hot wire on the dock in one hand and simply touch your finger to the water with the other. After picking up from the deck, unplug the boat and try it again to see if there's more current...There's not. You talk as if your neighbor's prop is only connected to your prop, which just isn't so.... AS to the breaker trip. If you connect AC hot to the engine block in his boat in seawater, I'd bet 50A would be just EASY! Seawater is a GREAT conductor. Fresh water is a fair conductor. Try it yourself. Simply drop the open plug from your boat into the water with the dock breaker turned on. There'll be a little buzzing underwater before the breaker overheats....and it eats the guts right out of the plug.... |
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