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Safety Grounding
12 questions By Tony R. Kuphaldt
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Question 1 of 12
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”?
Reveal answerThe “neutral” conductor in an AC power system is always made electrically common with the earth, while the non-grounded conductor in an AC power system is called the “hot” conductor:
Follow-up question #1: in a power circuit such as this, there is typically a single fuse or circuit breaker for overcurrent protection. Identify the best location to place this fuse or circuit breaker in the circuit.
Follow-up question #2: explain how to use a multimeter to identify the “hot” and “neutral” conductors of a power system such as this.
Notes:Ask your students what safety issues surround the “hot” and “neutral” conductors, respectively. What do the names imply about relative hazard, and why is this? Ask them to explain how these safety considerations impact the placement of the overcurrent protection device.
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Question 2 of 12
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?
Reveal answerAn ungrounded power system is unpredictable from the perspective of safety.
Notes:Be sure to discuss with your students the benefits and drawbacks of power system grounding. There are some instances where systems are left intentionally ungrounded because the safety benefit of grounding them is negligible (high-voltage power distribution systems may often be ungrounded for this reason). In low-voltage (120 volt) domestic power systems, though, grounding is required by law.
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Question 3 of 12
Is there any shock hazard posed to a person touching the metal case of this appliance? Explain your answer.
Reveal answerNo.
Follow-up question: what do the double-chevron symbols represent in a schematic diagram?
Notes:Even though no shock hazard presently exists in the circuit, ask your students to identify a condition where the “shorted” wire inside the appliance would pose a shock hazard. What would have to change in order for this wiring fault to pose a hazard?
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?