Question

Is this related to the previous question?

It can be a part of the previous question.Even otherwise also.

Thanks for your reply. But let me make it clear that it is these two points where I want to test are two earth bus bars.Clean earth and dirty earth.There is no potential on these bus bars.So can you explain now please.

You may *think* there is no potential between these two busbars, but you won't really know unless and until you check with a voltmeter. The very fact that one of them is called "dirty" earth while the other is called "clean" earth presupposes a difference of potential (at least during certain conditions) between them. If these two grounding busbars were always at exactly the same potential, there would be no need to have both of them in your system!

The difference of potential I am referring to may only be a few tenths of a volt, but it can be enough to skew the resistance indication of most digital multimeters. Always measure voltage between two points before trying to measure resistance, unless you know for a fact that there can never be potential between the two (e.g. measuring resistance of a resistor removed from any circuit).

Thank you very much for your reply.I totally agree with your answer.But let me ask ,"will it happen in the sameway In case if there is no potential". I mean two rods connected nowhere.Can you please clear my doubts given below.

1)In a panel Clean earth and Dirty earth bus bars are separated, but the loop is connected togethet at the end of all the connections.Why?

2)What is the resistance between Dirty eath and Clean earth with respect to the common earth rod.?

3)In the field junction box the cable shields are not connected to the common earth.Why?

The only other causes that come to mind explaining why your multimeter would read resistance differently with polarity is if you did not make good contact with your meter probe during one of the tests, or if you have an intermittent fault in your multimeter (or in the test leads).

As for your other questions, it appears they were answered well in another post by another user. Did you find his answers unclear? Your question #1 is somewhat unclear to me, as I do not know what you mean when you say "loop is connected together at the end of all the connections." A diagram would be helpful here.