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1621 Earth Ground Tester

Addendum to Users Manual

Earth Ground Resistance

Earth ground resistance consists of:

• resistance of the connecting lead to the earth ground electrode

• resistance of the earth ground electrode, earthing rod, earthing plate,

earthing strip, mesh earth electrode, and similar

• dissipation resistance (the resistance between the earth ground

electrode and soil potential)

The resistances of the connecting lead and earth ground electrode are

negligible (after correct dimensioning), so the earth ground resistance consists

primarily of the dissipation resistance.

To determine the exact earth ground conditions, an accurate measurement of

the dissipation resistance is required. Because dissipation resistance is

dependent on soil resistivity and the shape of the earth ground electrode, a

metrological check must be made even if the position of the earth ground

electrode and the condition of the soil are known.

When redesigning an earth ground system (for example, for lightning

protection), the resistance can be calculated using Table 1. As a basis for this

calculation, the soil resistivity of the location where the earth ground electrode

is to be installed must be known. See “Soil Resistivity.”

Summary of content (7 pages)

PAGE 1
621 Earth Ground Tester Addendum to Users Manual Earth Ground Resistance Earth ground resistance consists of: • resistance of the connecting lead to the earth ground electrode • resistance of the earth ground electrode, earthing rod, earthing plate, earthing strip, mesh earth electrode, and similar • dissipation resistance (the resistance between the earth ground electrode and soil potential) The resistances of the connecting lead and earth ground electrode are negligible (after correct dimensioning
PAGE 2
1621 Users Manual Addendum Table 1.
PAGE 3
Earth Ground Tester Addendum to Users Manual Soil Resistivity Soil resistivity (ρE) is the resistance measured between two opposing surfaces of a cube of soil, with a lateral length of 1 meter. Soil resistivity is measured in ohms-meters (em). See Figure 1. A = 1m E = 2 L L = 1m evp007.eps Figure 1. Soil Resistivity Soil resistivity primarily depends on soil type (like farming soil, dry sand, moist sand, concrete, gravel), although seasonal changes can also influence resistivity.
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1621 Users Manual Addendum 28 Earth Resistance RE 24 20 16 12 8 4 0 1 0 2 3 4 5 6 7 8 9 10 11 July Jan 12 Dec Temporal change of the earthing resistance of a set earth electrode. 14 12 Earth Resistance RE 10 8 6 4 2 0 0 1 2 Jan 3 4 5 6 7 July 8 9 10 11 12 Dec Temporal change of the earthing resistance of a buried earth electrode. evp008.eps Figure 2.
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Earth Ground Tester Addendum to Users Manual I Umeas G V I E ES I S H E S H RE RS RH UE evp009.eps Figure 3. Current Voltage Measuring Method Potential Gradient Area When electric current flows through an earth ground electrode, the area around the electrode develops what is called the “potential gradient area.” When selecting a location to insert the probe into the ground, you will need to determine the size of this potential gradient area because you must place the probe outside this area.
PAGE 6
1621 Users Manual Addendum that soil with good conductivity (low resistance) results in a steep voltage shape, and therefore a higher step voltage. If necessary, check the potential of such systems. To use the correct voltage drop from the earth ground resistance (the resistance between the earth ground electrode and the soil potential ΦE), ensure the probe is placed outside the potential gradient areas of the earth ground electrode and the auxiliary earth electrode.
PAGE 7
Earth Ground Tester Addendum to Users Manual Demonstration of Potential Gradient Area’s Influence on Measurements This section demonstrates how placing a probe inside the potential gradient area of an earth ground electrode leads to incorrect measurements. As shown in Figure 5, probes S1, S2 and S4 are positioned inside the potential gradient area, and probe S3 is positioned outside the potential gradient area.