Ground Rods

Ft there are /t number of conductors lengthwise and /t(, widthwise and = ntimber of grounding rods used in a grounding grid at a depth of h, then the total length of the buried conductors... 

For grids without or with only a few ground rods near the inner grid (not at the far ends) ... 

The resistivity of the soil in any particular location will be a function of moisture content, soil temperature and presence of dissolved salts. At a site where climatic conditions vary considerably throughout the year, earth electrodes should be buried at a depth where such changes will not affect the resistivity. Grounding rods are generally made of copper bonded onto a steel core. The copper provides a good connection to earth and offers a high corrosion resistance, while the steel core gives the mechanical... 

A low-flash-point solvent containing pigment was pumped through a bag filter into an open drum. The pigment drum was grounded by means of a grounding rod. Although the operation ran successfully for some time, one day there was a fire. 

It is hypothesized that one of two scenarios could have created the ignition. Possibly, the grounding rod was placed closer to the filter than previously, giving the conditions for a brush discharge between the filter and the grounding rod. It is also possible that the grounding rod wire was closer to the isolated drum than previously in this case a spark could have jumped between the drum and the grounding wire. 

Figure 7-4. Grounding. Electrical conductors are attached to the tank and then connected to a grounding rod.

GROUND ROD, COLD WATER PIPE, BUILDING STEEL GROUND RING, CONCRETE ENCASED ELECTRODE ETC. 

Earth resistance depends on the type of soil, its mineral composition, moisture content, and temperature. Table 5.2 provides the resistivity of various types of soils Table 5.3, the effect of moisture on soil resistivity and Table 5.4, the effect of temperature on soil resistivity. The information contained in the tables is used to illustrate the effect of various natural factors on soil resistivity. Table 5.5 shows the changes in earth resistance by using multiple ground rods. Note that, to realize the full benefits of multiple rods, the rods should be spaced an adequate distance apart. 

Change in Earth Resistance with Multiple Ground Rods... 

According to the NEC, ground rods should be not less than 8 ft long and should consist of the following ... 

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