Hi,
The current flowing through your body is determined by
the electrical resistance of the body and the voltage
applied.
Best regards,
Luciano
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Amount of Body Resistance.
Your body resistance varies greatly in different parts of your body.
A value of 1500 ohms is commonly used as the resistance between major
extremities of an average human body: hand to hand, or hand to foot.
Let’s use Ohm’s Law to figure how much current would flow through
your body if you accidentally grabbed a wire carrying 120 volts
alternating current (vac).
Ohm’s Law for figuring current is I = E/R.
Let E = 120 VAC— The voltage you grabbed
Let R = 1500 Ohms—Your (average) body resistance
Now let’s compute it:
I = 120/1500 = .080 amperes (80 milliamperes).
I = 80 milliamperes. So if you grabbed a 120-vac wire, 80 milliamperes
of current would flow through your body.
=============================================
Human reaction (at 60Hz)
1.1 milliamperes: PERCEPTION - A slight tingling sensation.
10 milliamperes: CAN'T LET GO - Arm and hand muscles close involuntarily. (120 lb. person).
16 milliamperes: CAN'T LET GO (175 lb. person).
18 milliamperes: CAN'T BREATHE - Paralysis of the chest muscles.
65 milliamperes: HEART FIBRILLATION - Rapid irregular contractions of the heart muscles. (Could be fatal).
=============================================
Now use the above table to determine the effect of 80 milliamperes
of electric shock. You can see that you may not be around long enough
to grab any more wires. You grabbed 80 milliamps of current!
That’s 15 milliamps beyond what could be fatal. It’s also 70 milliamps
beyond the can’t- let-go threshold, and 62 milliamps beyond what
is needed to cause you to stop breathing. It’s important to remember that
the 1500 ohms is just an average value. Body resistance varies from
person to person and may often be LESS than 1500 ohms. When your
skin is moist, your body resistance could be as low as 300 ohms. Also, breaks
in your skin at the point of contact reduce your skin resistance to nearly
zero. Skin resistance is only important when you’re handling voltages of
less than 240 volts. If you get shocked by more than 240 volts, the voltage
arc will burn through your skin and leave deep third-degree bums where it
enters your body.
Time of Current Flow.
The longer you’re being shocked, the more chance there is for your heart to
begin fibrillation. Fibrillation is the shocking of your heart into a useless
flutter. Most people who die from electric shock die from fibrillation.
Fibrillation in a normal adult is unlikely if the current in milliamperes is
less than 116/t, where t is the shock duration in seconds. The longer you
are shocked, the less current is needed to cause heart fibrillation. Here are
some examples of shock current levels and durations that would cause fibrillation:
21 milliamperes for 30 seconds
44 milliamperes for 7 seconds
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