Reno...
The physics describe above also under pins MHD power generators.
http://en.wikipedia.org/wiki/Magnetohydrodynamic_generatorIn a MHD design, the 'salt' used is typically potassium based.
The actual power density/ energy density is quite low. It's voltage potential is easily measured with a Fluke.
This Faraday effect does not occur in totally pure water. Btw, some areas of the country don't even have 'pure' water at the tap, potable, yes. So even the garden hose introduces more salts into the hot tub.
None of these units would be deemed to be 'salt water' tubs, per se. The salt concentrations are still so low as to merely taste bad.
The users get jolted because water is splashed out. Then when they exit -- obviously dripping -- they end up having one leg at zero potential/ the ground plane and their other still sticking straight into the hot tub.
If you're still unconvinced -- channel Dr. Faraday, Dr. Hall and the rest.
I've seen it, tested it, and cured it. BTW the hot tub in question was in Reno.
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If a device has a very well shielded motor then the above effect figures to be totally suppressed.
I've lost track of how many tub owners have gone onto the Internet to complain about phantom voltages -- near their hot tubs.
They're on the Internet -- because the service electricians -- more than one -- can't cure their problem -- and don't believe them -- or don't know what could POSSIBLY be causing the problem.
The typical owner assumes that the equipment is shorting -- and that's that. Of course, a true short would trip the GFCI -- if not the circuit breaker.
BTW, the impressed voltage also does a cracker jack job corroding any metal it contacts. No-one connects this galvanic, stepped up, corrosion with the Faraday effect.
At all times, these are low energies... kind of like building up a static charge by shuffling across carpeting.
The ability of an AC current to build up and impress a DC bias in transformer steels is covered by Buss, and aluded to in Ugly's. (short circuit calculation section)
The AC current flip flops the induced field. But because of imperfections in the magnetic domains of the rolled steel, it actually develops a slight DC bias. It favors one orientation more than the other. This effect is also at a (very) low level. It's never brought up in ordinary calculations or class discusions. You could be in the trade for fifty-years and never have to deal with it. It's counter intuitive, too. We're ALL taught that AC is symmetrical. But nature is complicated -- and actually is always slightly away from idealized physics.