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Electric Shock
17 questions By Tony R. Kuphaldt
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Question 10 of 17
Determine whether or not a shock hazard exists for a person standing on the ground, by touching any one of the points labeled in this circuit:
- • Point “A”
- • Point “B”
- • Point “C”
- • Point “D”
- • Point “E”
Reveal answer- • Point “A” dangerous to touch
- • Point “B” dangerous to touch
- • Point “C” dangerous to touch when motor is turned on
- • Point “D” safe to touch
- • Point “E” safe to touch
Notes:One suggestion for approaching this question is to ask your students to identify which of the power source conductors is “hot” and which one is “neutral,” then identify which points in the circuit are electrically common to either one or the other source conductors.
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Question 11 of 17
The following recommendations came from a flyer published by an electric power utility. Read and comment on their instructions regarding downed power lines:
- Assume any downed line is an energized power line. If a power line falls on your car while you are driving, slowly drive on until you are completely clear of the line (but do not drive over it). If your car is immobilized, stay in it until help arrives. Call for help from a cell phone if you have one. If you need to escape from a vehicle, such as for a car fire, jump clear of the car. Electricity is not only traveling through the vehicle, but may also be traveling in the ground around the area. Keep your arms crossed over your chest while you jump, and both feet together. Do NOT touch the vehicle and the ground at the same time. Once you land on the ground, shuffle clear of the area, keeping both feet together, on the ground, and touching at all times. Continue shuffling until you’re at least 30 feet from the accident site.
Why do you suppose the following actions were recommended?
- • Do not drive over a downed power line.
- • Stay in the car if possible. Do not touch the car and the ground at the same time.
- • Shuffle away from the car (rather than walk), with both feet together.
Reveal answerThese are all interesting points to consider as a group. I’ll let you figure out possible answers to these questions together in class.
Notes:The italicized text was taken directly from Puget Sound Energy’s April 2005 “Energywise” mail flyer. The points brought up were, I thought, very appropriate for discussion of electrical safety and theory. Personally, I question the suggestion of shuffling on both feet. I would suspect that running full-speed, where only one foot touches the ground at a time, and where you would leave the dangerous area faster, would be the safest option. I would be very interested to see if there is any scientific test data available on this subject!
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Question 12 of 17
The ignition system in a spark-ignition automobile engine produces voltages in the range of tens of thousands of volts: greater than the voltage levels typically used to distribute electric power through neighborhoods. Although this is capable of producing very painful electric shocks, the actual shock hazard it poses to a person is minimal. Why is this?
Reveal answerAutomotive ignition systems pose little direct shock hazard because of two factors: the resistance intrinsic to the high voltage circuit limits current to a fairly low value even without the resistance of a person’s body in the circuit; and the high voltage pulse lasts only a brief moment in time.
Notes:This is not to say that ignition systems pose no hazard, though. One of the main hazards is the reaction a shock produces in a person: namely, the jerking of limbs which could be dangerous in the proximity of moving parts. Emphasize that hazards may often be indirect: that something in itself may not be enough to hurt you, but you body’s reaction to that something is what poses the greater threat.
An example of this general principle is an allergic reaction. The threat here is the body’s over-reaction to an allergen, not the allergen itself!
Everything that was in here was interesing