Encyclopedia of Grounding (CA09040E)

NOTE: The distance from the fault to points A and B depend on fault magnitude and soil resistivity.

Resistance Approaches Constant Value Figure 8-13

Decrease in Current with Distance from the Earth Contact Point Figure 8-12

comes greater, the resistance shouldalso substan tially increase. However, the increase in distance is offset by an increase in cross section, as the current spreads throughout the earthen path. So, the result is a non-linear change in the region of the shells. Beyond the boundary of the shell (or between two remote shells shown in Fig. 8-13) the resistance tends to approach a constant value.

sidered constant. However, soil resistivity varies substantially with its make up. Some of the causes of variations are typesof soil, presenceandamount of moisture, sand or rock. The effective shell diameter equals twice that of the depth of the rod. Multiple rods used to make parallel connection paths to Earth tend to lose their parallel current carrying effectiveness if the shells substantially overlap.

If the soil resistivity were constant, the resistance of the path over the entire length might be con

MAINTENANCE OF PERSONAL PROTECTIVE EQUIPMENT

29CFR 1910.269 (n)(4)(i) [7] states that it is the utili ty’s responsibility toprovide “protectivegrounding equipment” that “shall be capable of conducting the maximum fault current that could flow (un derlined by the author for emphasis) at the point of grounding for the time necessary to clear the fault...” Further, 29 CFR 1910.269 (n)(4)(iii) states “Protective grounds shall have an impedance low enough so that they do not delay the operation of protectivedevices in caseof accidental energizing of the lines or equipment.” These two statements imply a responsibility upon the employer. While not specified, these two statements imply a responsibility to ensure equipment is maintained for use in a safe and usable state. In the past, little

CHANCE Ground Set Tester (C4033220)

CHANCE® LINEMAN GRADE TOOLS™

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