Hioki FT3151 - Appendix; Appx. 1 Earth Resistance

Appx.1
Appendix
Appx. 1 Earth resistance
The resistance between an earthing electrode and the ground is
usually called the earth resistance. To be exact, it is the sum of the
resistance of the earthing conductor, the contact resistance between
the earthing conductor and the ground, and the resistance of the
ground.
Earth resistance measurement differs from ordinary resistance
measurements, due to the factors described below.
• Polarization action
Because the ground has characteristics just like electrolyte, it has
the polarizing action: if DC current ows through the ground, an
electromotive force occurs in the opposite direction to the current,
interfering with correct measurement. Thus, a rectangular wave
or a sine wave with a frequency of between several tens heltzes
and 1 kHz is usually used to measure the earth resistance.
• Special conditions
Earth resistance is resistance between an earthing electrode and
the ground. It is not possible to take it out from the ground and
measure it.
Since the resistance of the ground is relatively high, a voltage
drop occurs near the electrode through which the current to be
measured ows. Thus, each of the electrodes, which consist
of electrode E, electrode S(P), and electrode H(C), needs to
be away from each other to approximately 10 m to accurately
measure the resistance of earthing electrode.
Appendix
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