Ground Fault calculation

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curveclamp

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I had the following question regarding a ground fault.
If Point A = 3 ohms and Point B = 6 ohms and Point A to Point B = 75 feet, where is the ground fault?
 
curveclamp said:
I had the following question regarding a ground fault.
If Point A = 3 ohms and Point B = 6 ohms and Point A to Point B = 75 feet, where is the ground fault?
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That question makes no sense, please rephrase. Are you trying to interpret a test report?
 
Welcome to the forum.:)

As Zog has pointed out, with the information you have given us we can't answer your question. Please try to give us more infromation so we can help you.

Chris
 
Ground Fault Calculation

Ground Fault Calculation

That was a question on an exam. That was everything given in its entirety with nothing omitted. But the answers were 15 feet, 35 feet, 50 feet and 75 feet. I agree that info is lacking, but that is it.
Thanks!
 
curveclamp said:
That was a question on an exam. That was everything given in its entirety with nothing omitted. But the answers were 15 feet, 35 feet, 50 feet and 75 feet. I agree that info is lacking, but that is it.
Thanks!
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Based on this I would infer that the question should have been "Given the resistance to ground from point A = 3 ohms and point B = 6 ohms. The length from point A to point B is 75'. How far is the ground from point A?"
 
curveclamp said:
That was a question on an exam. That was everything given in its entirety with nothing omitted. But the answers were 15 feet, 35 feet, 50 feet and 75 feet. I agree that info is lacking, but that is it.
Thanks!
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Oh, well in that case, the answer is 50 feet.

Based on the theory that (c) is most commonly the right answer on multiple choice tests.
 
jghrist said:
Oh, well in that case, the answer is 50 feet.

Based on the theory that (c) is most commonly the right answer on multiple choice tests.
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That depends on the test. I took the P.E. in April and they made it clear that they had been careful to make sure the answers were evenly distributed.

Edit: I still guessed (C) on the ones I didn't know, but I also failed the test. :) There is no substitute for knowing how to work the problem. :D
 
drbond24 said:
That depends on the test. I took the P.E. in April and they made it clear that they had been careful to make sure the answers were evenly distributed.

Edit: I still guessed (C) on the ones I didn't know, but I also failed the test. :) There is no substitute for knowing how to work the problem. :D
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In that case use the clock method, you need an answer, look at the second hand and what quadrant it is in.
 
(Warning, this solution requires a lot of assumptions)

Well, assuming A and B are two points on a wire, running left to right in front of you, you could have two solutions;

1. The fault could be one third of the way between points A and B. Now, from which point you would measure this would be arbitrary...it would either be 25 feet from A, or 50 feet from B.

2. The fault could also be 75 feet "left" of A. The problem didn't specify, among other things, the resistivity of the wire. It also did not specify the wire was only between A and B.

My opinion is that even if you get this problem right, you come away feeling a little stupider for even having answered it...but if I was taking a test and it counted, I would give the "50" answer and pray.

This whole things smacks of some teachers giving multiple choice exams full of "best" answers. Hated those guys in school.
 
I think Jim is on the right track with his interpretation. If the question was worded better, it would be a good example of how substation relaying (for example) works to find the approximate location of a fault by calculating impedance from voltage and current values. The answer would be 25 feet from point A and 50 feet from point B.
 
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