Hioki FT6031 - Appendix 1 Earth Resistance

Appx.
1
Appendix
Appendix 1 Earth Resistance
The resistance between earthing electrode and ground is usually
called earth resistance. To be exact, it is the sum of the resistance
of earthing conductor, the contact resistance between earthing
conductor and ground, and the resistance of ground.
Earth resistance is different from commonly known resistors and
has the following special characteristics.
• Polarizing action
Since the ground has characteristics just like electrolyte, it
has the polarizing action, and if DC current ows through, an
electromotive force occurs in the opposite direction to the current,
interfering with correct measurement. Therefore, rectangular
wave or sine wave of several tens Hz to 1 kHz is usually used to
measure the earth resistance.
• Special conguration
Earth resistance is a resistance between earthing electrode
and ground. It is not possible to take it out from the ground and
measure it.
Since the resistivity of ground is relatively high, a voltage drop
occurs near the electrode through which the current to be
measured ows. Therefore, each electrode (E electrode, S(P)
electrode, H(C) electrode) needs to be away from each other to
approx. 10 m to accurately measure the resistance of earthing
electrode.
• Presence of disturbance factors
There are disturbance factors such as effects from earth potential
and auxiliary earthing electrode in the measurement of earth
resistance.
The earth potential caused by a leakage current from a device
that has been connected to the earthing electrode affects the
measured value as it is superimposed over the signal to be
Appendix