FC138001@ysub.ysu.edu (Phil Munro) (04/24/91)
> ... >I have some friends that live near some big voltage lines in Mason, >NH. They have a fiberglass hot-tub sitting on a cement slab. One day >I was halfway into the tub, with one foot on the slab and one in the >water, when I recieved a pretty healthy zap. This happened to enough >people that an electrician was called in, and it was eventually >determined that the tub was floating, electrically, at some distance >above ground, and the potential in it was getting there do to some >potential gradient (in the soil?) coming from the power lines. This >sounds like 'stray voltage' to me, but I still don't quite understand >the mechanism. > Has anyone considered that the hot tub of water sitting in the open field will evaporate, and when water molecules evaporate they carry some charge with them. (I think this is the way charge is built up in clouds, producing lightning!) Could it be that this is what is happening? It was already stated that the water was floating electrically. The question is where does the charge come from? It does not seem obvious to me that AC power lines would have an effect on this. --Phil
gandrews@netcom.COM (Greg Andrews) (04/24/91)
In article <91113.143901FC138001@ysub.ysu.edu> FC138001@ysub.ysu.edu (Phil Munro) writes: >> ... >>This happened to enough people that an electrician was called in, and >>it was eventually determined that the tub was floating, electrically, >>at some distance above ground, and the potential in it was getting there >>due to some potential gradient (in the soil?) coming from the power lines. >>This sounds like 'stray voltage' to me, but I still don't quite understand >>the mechanism. >> > Has anyone considered that the hot tub of water sitting in the open >field will evaporate, and when water molecules evaporate they carry some >charge with them. (I think this is the way charge is built up in >clouds, producing lightning!) > > Could it be that this is what is happening? It was already stated >that the water was floating electrically. The question is where does >the charge come from? It does not seem obvious to me that AC power >lines would have an effect on this. > No, evaporation would not produce that big a charge in the water. To produce a charge in the manner you're thinking, you would have to be losing electrons or protons from the hydrogen and oxygen atoms. Evaporation doesn't do that. You don't lose subatomic particles, you lose whole molecules. The most likely source of the charge is the wall power to the pump. If there were no ground supplied to the pump, or the ground wire is "grounded" at a point far away from the dirt around the hot tub (e.g. through a long extension cord), then you could have this problem. The water makes contact with the metal housing of the pump, which is "grounded" through the power cable. The pump and the water are held to the voltage level that represents "ground" back at the house, but the dirt (or cement) around the hot tub is at a different potential than the house. Whenever someone bridges the gap between the local dirt "ground" and the house "ground", current flows and they feel the electrical shock. -- .------------------------------------------------------------------------. | Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | | | Internet: gandrews@netcom.COM | `------------------------------------------------------------------------'
jfa0522@hertz.njit.edu (john f andrews ece) (04/25/91)
In article <1991Apr24.024228.25848@netcom.COM> gandrews@netcom.COM (Greg Andrews) writes: >In article <91113.143901FC138001@ysub.ysu.edu> FC138001@ysub.ysu.edu (Phil Munro) writes: >>> ... >>>it was eventually determined that the tub was floating, electrically, >>>at some distance above ground, and the potential in it was getting there >>>due to some potential gradient (in the soil?) coming from the power lines. >>>This sounds like 'stray voltage' to me, but I still don't quite understand >>>the mechanism. >>> stuff deleted to appease the campus mail server... > >The most likely source of the charge is the wall power to the pump. >If there were no ground supplied to the pump, or the ground wire is >"grounded" at a point far away from the dirt around the hot tub >(e.g. through a long extension cord), then you could have this problem. > >-- >.------------------------------------------------------------------------. >| Greg Andrews | UUCP: {apple,amdahl,claris}!netcom!gandrews | >| | Internet: gandrews@netcom.COM | >`------------------------------------------------------------------------' And if indeed this were the case, a simple copper grounding spike on-site, (metal-tub-frame to earth beneath the concrete slab) solves the problem...