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Safety Grounding
12 questions By Tony R. Kuphaldt
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Question 4 of 12
Is there any shock hazard posed to a person touching the metal case of this appliance? Explain your answer.
Reveal answerYes, if the power switch is turned “on”.
Notes:Aside from removing the “short” connecting the power conductor to the metal case of the appliance, what else could be done to eliminate the shock hazard in this scenario? Discuss this with your students.
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Question 5 of 12
The metal case of this appliance is grounded by means of a third conductor:
Explain how this grounding connection makes the appliance safer for anyone touching its metal case.
Reveal answerThe ground wire connection makes the metal case of the appliance electrically common with earth ground.
Notes:Ask your students to explain why the case’s electrical commonality with earth makes it safer to touch. What do they know about “electrically common points” in a circuit, and voltage between those points?
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Question 6 of 12
What is a polarized power plug, and what does this have to do with electrical safety?
Reveal answerA “polarized” power plug is one that is designed to plug into a power receptacle one way only (i.e. it cannot be reversed). Usually this is accomplished by the use of one “prong” on the plug being wider than the other, with matching-width holes in the receptacle.
Notes:Discuss with your students the relative merits of polarized plugs versus three-wire plugs that provide a hard ground connection with the frame of the electrical device. Which plug type provides a greater level of safety? Why?
For question 9, how are you supposed to distinguish between ground and neutral using a voltmeter? Is there an assumption that the bottom conductor is ground?