ERICO EST401 ERITECH Clamp-on Ground Resistance Tester - Manual (Page 24)

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Q. Can the Clamp-on method be used effectively on high tension towers despite
the distance or spacing between them?
A. Yes. Extended distances will not adversely affect the measurement results. The important
factor is that it be a multiple electrode system.
Q. Does the grounding electrode have to be disconnected and isolated as is
required when using the “Fall-Of-Potential” test with auxiliary electrodes?
A. No. Actually the electrode must be connected to the system to provide the path for test
signal injection as well as to provide the background impedance necessary as the reference.
Additionally, if the tested rod is poorly bonded to the ground connector, a high reading will
be present.
Q. Does this mean I am not able to test an independent electrode?
A. No, however as soon as the connection is made to a multiple electrode system,
usually provided by the connection to the system neutral, you can clamp on and make
a measurement.
Q. Must the instrument be clamped directly on the electrode?
A. No, the instrument will provide valid measurement results when clamped on to the
electrode or the conductor leading to the grounding electrode. The reading through the
conductor will also verify not only the grounding electrode resistance, but connections
of the ground wire to the rest of the system.
Q. Does the system under test have to be energized or de-energized to perform
the test?
A. We are measuring the grounding network. The only requirements are that ground
connections be made to the system under test and that the voltage-to-ground at the
tested point not exceed the instrument rating.
Q. Can the clamp-on method be used for substation grid resistance testing?
A. It depends. It can be used as long as the instrument can be clamped onto a point on
the grounding system at a common point where it ties to the system neutral. Testing a
grid must be treated as if it were a single electrode. Often, clamping on to points within
the grid system will yield a closed loop reading.
Q. How does clamp-on ground testing compare with the standard
“Fall-Of-Potential” test?
A. Empirical testing has validated that when performed correctly, both methods will provide
accurate and repeatable readings for ground electrode resistance.
Q. How large a conductor can the jaw accommodate?
A. The inner diameter of the jaw is 1.25" and can accommodate cables up to 1000 kcmil.
Commonly Asked Questions for
Clamp-on Ground Resistance Measurements
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