Electrical Safety Example
• A person accidentally grabs conductors
connected to each end of a DC voltage
source in each hand.
– What is the minimum source voltage that can
produce electrical shock sufficient to cause
paralysis, preventing the person from letting
go of the conductors?
– Assume that the resistance of the arm is
400Ω, the trunk is 50Ω, and the leg is 200Ω.
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+ V
-
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+ V
-
Current flows
through the arms
RA = 400 Ω
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Safety Example continued
• From Table 2.1, the minimum current for
muscle paralysis is 50 mA.
V  iRarms  (50mA)(400  400)
V  40V
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Safety Example continued
• Is there a significant risk of this type of
accident occurring while servicing a
personal computer, which typically has 5V
and 12V sources?
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Safety Example continued
• Compute the maximum current that can be
drawn from the computer power supply.
imax
12V

 15mA
800
• This current will cause a shock, but will not
cause muscle paralysis.
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