Moshe Valdman asks about 12 volts DC applied between the
hand and other body parts.
1. Resistance.
The human body resistance is not a constant.
If you have measured yourself with an ohmmeter, you will
have noticed that the body resistance is not a constant,
and continually reduced in value for the duration of the
measurement.
The body resistance is a function of many variables,
including contact location (on the body), contact area,
skin condition, time of day, skin temperature, applied
voltage, duration of applied voltage, etc.
Depending on the preceding variables, the body resistance
will measure (with an ohmmeter) anywhere from a maximum of
1 megohm down to a minimum of 5 kohm.
Increased voltage accelerates the decrease in body resistance.
Depending on the contact location, contact area, and duration
of applied voltage, with 12 volts dc applied to the body, you
can expect a continuous decrease in body resistance.
2. Current.
Current in the body is determined by Ohm's Law. Given 12
volts DC, and continuosly decreasing body resistance, the
current in the body will continuosly increase.
The body resistance may approach 5 kohms, which means the body
current would approach 2.4 milliamperes.
Depending on the individual, some persons may experience a
sensation of electric shock after several minutes, while others
will never experience a sensation of electric shock.
3. Medical or other regulations.
I don't know of any...
4. Risks.
Human reaction to electric current has a very high three-
sigma variation. Short-term (i.e., less than one minute) and
intermittant contact with 12 volts DC probably will have little
or no noticable effect.
But, long-term effects of low voltage have not been studied.
Fortunately, at low voltages such as 12 volts, I would expect
that the body response would come on slowly so that one could
anticipate any unwanted effects.
5. Standards.
IEC 479 is the reference standard for effects of current on the
body.
But, this document does not address voltage sources such as 12
volts DC.
Best regards,
Richard Nute
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|Richard Nute |Quality Department |
|Hewlett-Packard Company |Product Regulations Group |
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