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Thread: Hypothetical

  1. #41
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    Sep 2008
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    Quote Originally Posted by kwired View Post
    the common misconception is that the hair dryer should throw sparks or blow up when immersed in the water.
    But the reality wouldn't provide anything like the drama the film producers want.......
    Si hoc legere scis nimium eruditionis habes.

  2. #42
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    Quote Originally Posted by GoldDigger View Post
    But all of those that I have seen require you to add a significant amount of salt to the water.

    Sent from my XT1585 using Tapatalk
    Had one like I described when I was a kid. We never added any salt, just tap water, but we have fairly "hard" water around here so salt likely not necessary.

    You can't burn it out when water level is too low like you can an element type heater.

  3. #43
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    170911-2517 EDT

    From a theoretical perspective this is a field mapping problem.

    Back when I was an EE student at the U of M every EE to graduate had to pass a senior course from A. D. Moore. This was mostly on hand field mapping and heat transfer.

    A. D. Moore was a character. He was an Eminent Member of Eta Kappa Nu, and in 1928 President of Tau Beta Pi. He was a professor at the U of M from 1916 to 1965. See:
    http://www.public-art.umich.edu/the_...ampus/north/10
    https://www.tbp.org/fellowships.cfm
    https://www.tbp.org/about/F85FirstCentury.pdf

    Today I suspect that no one is taught to do graphical field maps. But the concepts are very useful.

    The question of this post can be somewhat analyzed with a glass tray of tap water and some electrodes placed to simulate the problem. Use 12 V AC 60 Hz. and a high impedance AC meter.

    But never in the real world of moderate voltages of 120 and above work with the system hot without proper protection. Possibly even 12 V and above.

    .

  4. #44
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
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    170812-1307 EDT

    An experiment you could perform.

    Find a plastic tub 2 to 3 ft long by about 1.5 ft and at least 8 inches deep.

    On the bottom of the tub put a conductive plate brought out with a wire. Use an insulated wire. This will be your ground, equivalent to a wet cement floor.

    For power use a small transformer, 25 W would be more than adequate, larger won't be a problem. Output voltage anywhere from 6 to 24 V.

    Cut a suitable length of #14 Romex. Connect the Romex to a duplex receptacle in a metal box with a metal cover. Obviously all connections would be done as expected.

    At the power supply end of the Romex connect EGC, neutral, and the ground plate in the tub together, and these go to one side of the transformer output. Nothing is connected to real earth or the neutral to the transformer primary. This test is basically isolated from real earth.

    The secondary EGC does not need to be unearthed, there is just no need to earth it.

    Connect the Romex hot to the other end of the transformer secondary.

    The Romex EGC will be the reference for your voltage measurements.

    Completely fill the tub with tap water. Almost anywhere this water will have sufficient conductivity. If not, add some salt and mix uniformly.

    Put the electrical box in the water, and it must not touch the ground plate. Clamp the box in position so it does not move.

    Get a short piece of enameled copper wire, magnet wire, to use as an insulated probe. This makes a point contact probe, just the end of the wire. #12 might be good, but #18 probably would be stiff enough.

    Apply voltage to the transformer primary.

    Between the secondary isolated EGC, and the insulated probe measure the voltage at various points in the water. This will give you a map of voltages at various points. Use a high impedance meter, 10 megohm.

    I have not done this specific experiment, but I have done similar experiments.

    After doing the metal box experiment change to a plastic box and plastic cover. I don't know how much difference you will see.

    The biggest voltage gradient will be near the duplex hot slot(s).

    With the metal box properly connected to its floating EGC I doubt that you will see a very large voltage gradient virtually anywhere in the water except close to the duplex HOT socket point.

    What you are concerned with is the probe voltage as a percentage of the transformer secondary voltage.

    .
    Last edited by gar; 09-12-17 at 02:22 PM.

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