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Sep 2, 2010 3:57 PM

Decide whether the following statement is true or false: A motor and its 480V supply transformer are each provided with a ground rod, so it's safe to put one foot on each ground rod. Now, give the reason for your answer.

Many people will answer “true,” and their reason will be that the two rods are at equipotential because both are grounded. The correct answer is actually “false.” Earth has significant resistance, and thus there are differences of potential between two grounding points. This is why, for example, we use the fall of potential method in grounding work.

But doesn't electricity take the path of least resistance? Draw a parallel circuit with a 100Ω resistor and a 200Ω resistor, and solve for current in each path. As you can see, electricity doesn't take the path of least resistance. Grounding does not remove potentially lethal shock hazards.

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