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Devise to shock earth worm

Discussion in 'Electrical Engineering' started by John, Nov 22, 2007.

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  1. John

    John Guest

    I had an uncle who used a electric devise to get worms from the lawn for use
    as fish bait. This devise had a pointed ~ 1/4" metal rod protected by a
    spring loaded plastic sleeve which was inserted into the ground. Apparently
    the sleeve was intended to prevent shocking the user. Then the plug was
    connected to the an electric outlet. The worms in the an area of several
    sq. ft would come to the surface and be caught. This devise worked better
    when the ground was wet or at least damp. How did it work and why didn't it
    blow a fuse?

    Thanks for comments

  2. I have read that worms do not like some electricity going through them.
    Some electricity going through them will cause that they go to surface.

    When a metal rod with some voltage (different than
    the overal ground potential is) is pushed to ground, it will
    cause a local voltage potential very near to rod rise to the
    voltager applied to rod. When going more distance away from rod,
    the potential will drop down to the actual ground potential
    some meters away from rod. This potential difference is caused by
    ground resistance and the current flowing on ground (starting
    from the rod). When worms are in ground where the current flows,
    some part of current flows through them.

    This device did not blow the fuse because either the grounding
    resistance of the this rod was high enough that the current
    flowing through it will not blow fuse (for example 20 ohms
    gournding resistance causes 6A current for 120V AC and
    will not blow 15A fuze, if grounding resistance is 4 ohms then
    current will be 30 amperes that will blow 15A fuse within some minutes)
    or the system in use had some built in current limiting device
    that makes sure that current is within limits allowed by fuses.

    This kind of device sounds to me like a very dangerous equipment
    that would be quite impossible to fullfill the modern electrical
    safety regulations.
  3. To my knowledge telephone ringing frequencies are less dangerous
    for humans than 50 Hz or 60 Hz electrical power.
    The telephone line frequencies are lower (20-25 Hz quite often).
    They can be painful, activate musches heavily, but with then
    is it much less propably that you "stick" to the power source
    (getting constant power going through you) and is less propable
    that they disturb your heart operation in bad way
    (ventricular fibrillation, cardiac arrest etc.).

    The perception of electric shock can be different depending on the
    voltage, duration, current, path taken, frequency, etc. Current
    entering the hand has a threshold of perception of about 5 to 10 mA
    (milliampere) for DC and about 1 to 10 mA for AC at 60 Hz. Shock
    perception declines with increasing frequency, ultimately disappearing
    at frequencies above 15-20 kHz.

    A low-voltage (110 to 220 V), 60-Hz AC current traveling through the
    chest for a fraction of a second may induce ventricular fibrillation
    at currents as low as 60mA. With DC, 300 to 500 mA is required. If the
    current has a direct pathway to the heart (eg, via a cardiac catheter
    or other electrodes), a much lower current of less than 1 mA, (AC or
    DC) can cause fibrillation. Fibrillations are usually lethal because
    all the heart muscle cells move independently. Above 200mA, muscle
    contractions are so strong that the heart muscles cannot move at all.

    DC tends to cause continuous muscular contractions that make the
    victim hold on to a live conductor, thereby increasing the risk of
    deep tissue burns. On the other hand, mains-frequency AC tends to
    interfere more with the heart's electrical pacemaker, leading to an
    increased risk of fibrillation. AC at higher frequencies holds a
    different mixture of hazards, such as RF burns and the possibility of
    tissue damage with no immediate sensation of pain. Generally, higher
    frequency AC current tends to run along the skin rather than
    penetrating and touching vital organs such as the heart.

    The frequency of the AC has lots to do with the effect on the human
    body. Unfortunately, 60 cycles is in the most harmful range. At the
    house voltage frequency, as little as 25 volts can kill. On the other
    hand, people have withstood 40,000 volts at a frequency of a million
    cycles or so without fatal effects.
    A very little current can produce a lethal electric shock. Any current
    over 10 ma. will result in serious shock.

    Normal ringing voltage is about 100 volts at 20 Hz, and it is truely
    nasty stuff. Getting jerked around by 20 Hz current will teach some
    true respect. Don't confuse that with a relatively mild 60 Hz shock.
    (Either one can kill you.)
    But, the ring voltage is current limited.
    And I'll admit to being semi
    scared to death of 60 Hz house current, but I'm also ten times as
    scared of 20 Hz ring current. It *HURTS*!

    However, when the phone rings, a series of high voltage AC surges come
    through the lines, up to 100 volts, and this can be dangerous,
    especially to people with health conditions, pacemakers, etc.

    Yes it will limit that quite much.
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