S1400T-2808B Page 3-4 Section 3 - Grounding & Isolation
Figure 3-3 - Basic Ground Bed Soil Test Setup with Additional Ground Rods
If the Megger still reads more than 10 ohms, mix a generous amount of cooking salt, ice
cream salt or rock salt with water and then pour about 2.5 to 5 gallons of this solution
around each rod (including the test rods). Wait 15 minutes and re-test the soil. If the test
fails, the soil is poor and a ‘Poor Soil Ground Bed’ will have to be constructed.
Figure 3-4 shows a typical Poor Soil Ground Bed Electrode. A Poor Soil Ground Bed will
typically consists of four or more 10-foot long electrodes stacked vertically and separated by
earth. Figure 3-5 shows the construction of a Poor Soil Ground Bed. For some poor soil
sites, the ground bed will be constructed of many layers of ‘Capacitive Couplings’ as
illustrated. In extremely poor soil sites one or more 3’ by 3’ copper plates (12 gauge or 1/16”
thick) will have to be buried in place of the electrodes.
Figure 3-4 - Ground Electrode Construction for Poor Soil Conditions
3.3.1.3 Dry, Sandy or Rocky Soil
Very dry soil will not provide enough free ions for good conductance and a single ground rod
will not be effective. A buried counterpoise or copper screen is recommended for these
situations. It will be necessary to keep the soil moist through regular applications of water.
To Next Page
Loading...
