Omicron CPC 100 - Page 209

Resistance
7 - 15
Figure 9:
Measuring the ground
resistance of small
ground systems
Note: Do not touch the test probe without insulating gloves outside of the
substation area. In case of a high-current ground fault within the
substation during the test, considerably high voltages could arise in
any wire connected to the substation and leading away from it.
Δ U
3 ... 5 x a
≈10 x a
Substation ground
a = size of the earthing system
a
a
Auxiliary
electrode
U
Auxiliary
electrode
I
I
90º
(Bird’s-eye view)