Question 1

In simple AC power systems, one of the two conductors is typically called the hot, while the other conductor is typically called the neutral. What distinguishes the “hot” conductor from the “neutral” conductor in such a system? In other words, what exactly determines whether a conductor will be called either “hot” or “neutral”?



 

Question 2

Explain why most electrical power systems have one of their current-carrying conductors connected to earth ground (“grounded”). Why not just leave all power conductors ungrounded? Would this not reduce electric shock hazard?

 

Question 3

Is there any shock hazard posed to a person touching the metal case of this appliance? Explain your answer.



 

Question 4

Is there any shock hazard posed to a person touching the metal case of this appliance? Explain your answer.



 

Question 5

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.

 

Question 6

What is a polarized power plug, and what does this have to do with electrical safety?

 

Question 7

The presence of a “ground” wire increases the degree of electrical safety for anyone using an electrical appliance. It entails having a third “prong” on the power plug, connecting with a third hole on the power receptacle, which connects to a separate wire running all the way back to the power system’s grounding point:



But why not eliminate all that extra wiring, and simply connect the third hole on the power receptacle to the “neutral” wire?



Why would this idea be unwise?

 

Question 8

In the United States of America, the National Electrical Code (NEC) specifies certain color codes to be used for designation of grounded, grounding, and ungrounded wires in AC power systems. First, relate the terms “hot,” “neutral,” and “ground” to the terms “grounded,” “grounding,” and “ungrounded”. Then, describe the acceptable color codes for each conductor. Also, note the article and section of the National Electrical Code under which these specifications are found.

 

Question 9

Explain how you would use a voltmeter to identify the “hot,” “neutral,” and “ground” conductors on a three-prong power receptacle:



 

Question 10

Special safety devices called Ground Fault Current Interrupters, or GFCI’s, reduce the risk of shock hazard in electrical systems even where there is no ground conductor. Explain the operating principle of a GFCI. How are they able to sense a “ground fault” condition, so as to automatically turn off power to a receptacle?

 

Question 11

Suppose a GFCI is rated to “trip” with a ground fault current of 5 mA. Given a source voltage of 115 volts, calculate the ground fault resistance range required to trip.

 

Question 12

I once watched a television advertisement for an electric drill, in which one of the people selling this product claimed it was “double-insulated,” to which the other person replied, “So it doesn’t get hot in your hand, right?”

What do you think of this comment? Is this what “double-insulated” means?

 


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