Site Considerations for Equipment Installation, Grounding, and Wiring Manual
D301452X012
September 2019
Grounding and Isolation 9
3.3.1.2 Soil Types
Table 3-1 details good and poor soil types.
Table 3-1: Soil Types
Always test ground beds for conductivity prior to placing any equipment in service. This section
provides a brief description of ground bed testing in both “good soil” and “poor soil.” Details on
this test are described in the National Electrical Code Handbook. Once you establish a reliable
ground, test it routinely to preserve system integrity.
Figure 3-2 shows the test setup for “good soil” conditions.
Figure 3-2: Basic Ground Bed Soil Test Setup
If the ground resistance testing unit (GRTU, such as a Meggar
®
High-Performance Ground
Resistance Tester or an Associated Research Vibroground) reads less than 5 ohms, consider the
ground “good”: the lower the resistance, the better the earth ground. If the GRTU reads more than
10 ohms, the ground is “poor.” If a poor ground is indicated, drive one or more additional ground
rods connected 10 feet from the main ground rod into the soil and interconnect them via bare
AWG 0000 copper wire and 1” x ¼-20 cable clamps (as shown in Figure 3-3).
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