Notes on resistance of gas-pipe grounds
Proceedings of the American Institute of Electrical Engineers
Earth connections in electric circuits are frequently made by driving a gas pipe into the ground. Such grounds are of fairly high resistance, and therefore not permissible where a low resist ance ground is required. Their great simplicity and cheapness makes them desirable, wheie very low ground resistance is not necessary, as for discharging static charges, eai thing overhead ground-wires, etc. To get data on the resistance offered by such gas pipe grounds, their permanence, and the variation
... and the variation of the resistance with the seasons, an investigation was started two years ago. Three gas pipes of 2.5 in. diameter were driven into the ground at distances of 15.75 ft. between I and II, and 7.4 ft. between II and III, in the lawn adjacent to Dr. Steinmetz's laboratory. The soil is a clay loam, overlaying shale rock a few feet below the surface. The pipes are driven into the following depth: I. 3.75 ft. II. 2.75 " III. 3.10 " The resistance of the three grounds was measured with an alter-, nating 60-cycle current of 120 volts, and as return ground was used the system of the city water pipes. This return ground showed to be less than 0.01 ohms. It was therefore neglected. Readings were taken at irregular intervals from August 1905 to August 1906, and daily from September 1, 1906 to date: during fall and spring, morning and evening readings were taken to see whether the daily temperature variation had any effects. These however, were found so small that in the attached curves the daily average has been used.