[Jewelry making - Article 00026] - [Orchid] Electrical shocks

[jesse brennan]

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    I posted this a while back. It  points out the potential dangers that
     very seriously apply to electrical shocks. These can become a lethal
    thing  with the normal 115 volt supply voltage in North America--- In
    the parts of the world with 240 volt household supply the risks are
    much greater. 

    Ground fault interrupters (GFI) have been required in the US and I
    believe Canada about 25 plus years. They are required in bathrooms,
    wet areas of kitchens and on exterior circuits as a minimum. I am
    out of date on the codes but they will not have been reduced.
    Issolation transformers are required  for electrical equipment in
    hospital environments. The Canadian codes are equal or possibly
    superior to the US codes. I know nothing about requirements in other
     parts of the world. 

jesse

    1) Voltage doesn't  kill, current does.
    2) You are just a large resistor.

    The following is taken from :

    http://www.physics.udel.edu/~watson/scen103/colloq2000/safety.html

    Note that the current has to pass thru the chest.   You should visit
    the link. 

    Current effects on human body, current through chest (A, amps) 

    <0.01  tingling or imperceptible
    0.02  painful, cannot let go
    0.03  breathing disturbed
    0.07  breathing very difficult
    0.10  death due to fibrillation
    >0.20  no fibrillation, but severe burning, no breathing

    Mariss  ran these tests on himself:

    I set my multimeter to "mA", connected it to a 60VDC supply, then
    washed my hands but didn't dry them. I grabbed my multimeter probes
    in each hand and measured 1.2mA of current. 

    I then sprinkled table salt on my still wet hands and tried again.
    The best I could get was 9.8mA and a barely perceptable tingling. 

    The internal resistance of a human body is about 500 Ohms. If your
    skin were removed, it would then take about 50 volts to be lethal. 

    High voltages (115VAC, 230VAC) can kill by burning thru the skin at
    the point of contact and then connecting to the much lower internal
    body resistance. This takes time though, about 15 to 30 seconds at
    230VAC. The heat generated is about 20W at the point of contact
    (200V times 100mA) and takes that long to burn thru the skin. 

    The 9.8mA at 60V I tried generated a bit more than 1/2W (588mW) and
    could do that; the body is simply too much of a heat-sink at that
    power level. 

    As another reference said: "Electrocution is very difficult at
    voltages below 100V, you must really work at it to succeed". 

    Safety suggestions: 

    1) Use only 1 hand when working with high voltages (115VAC or more).
    Keep the other hand behind your back; never rest it on anything. 

    2) Don't stand barefoot on a concrete floor or don't stand on a wet
    concrete floor with shoes on when working with high voltages. 

    3) When touching a high voltage, do it with the back of your hand or
    back of your finger first. Should there be a shock, muscle
    contraction will pull your hand away from instead of onto the
    conductor. 

    4) Keep your hands dry. If they get sweaty, dry them often. 

    5) Obviously, have the power off. Off means the plug is pulled from
    the wall. Always double check to see the pulled plug before you get
    into the equipment if you walked away from it for even a minute.
    Someone could have plugged it back in during your absence. 

    Mariss Freimanis

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