instrument earth impedance 1

[ELEC07]

dear all
i made a test of instrument earth impedance and i found it 4.6 ohm. i need to know if this is acceptable value or not and the electtrical standards related to that
thanks in advance

 

[waross]

Mr. Che;
You misunderstand the common use of the stakeless tests and the stakeless measurements.
How do you measure ground resistance without a reference ground?

In recognition of your contributions to Eng-Tips and of your knowledge, I will try to explain stakeless testing.
The tester forms a transformer with a one turn secondary winding.
Think of a CT in reverse as the CT is a transformer with a one turn primary winding.
The instantaneous current flow is from the tester to the electrode under test, from there through the earth to the reference grid or electrode, up the reference electrode and back to the tester.

Ground resistance specs are generally expressed as "Less than X Ohms".
X may be 5 Ohms, 25 Ohms or some other value selected by the design engineer or required by applicable engineering standards.
The result of a stakeless test may be expressed as "Less than X Ohms".
Often the resistance to ground of the reference grid will be much less than the resistance to ground of the electrode under test.
The stakeless test is widely used and is quick and easy.
The results are accurate within the limitations of the test.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr waross
W. " .... You misunderstand the common use of the stakeless tests and the stakeless measurements. How do you measure ground resistance without a reference ground? ...".
C1. Thank you for your explanation and the sketch which is also described in the documents of the instrument manufacture. Irrespective of the brand, size and shape, the design/operation principle is the same i.e. stakeless method.
C2. My basis opinion is: when electrode A is X ohm and electrode B of Y ohm, when connected in parallel; the value shall be X or lower. But NOT (X+Y) ohm. This is the usual case in practice. When a single electrode exceeds the required value say X ohm ; you plant another electrode B as far apart from A and connect them in parallel. You expect the paralleled A and B to be lower than X ohm. This is the main reason why you plant additional electrode B.
C3. We have different opinion/expectation.
C4. I wish to keep the case closed.
Che Kuan Yau (Singapore)