Discussion on “measuring stray currents in underground pipes” (Hering), Boston, Mass., June 28, 1912. (see proceedings for June, 1912)

Albert F. Ganz: In electrolysis surveys it is important to measure the currents flowing on pipes. The most common method used for this measurement is to treat part of the pipe length as a shunt, and to measure the drop across this shunt with a sensitive millivoltmeter, and then to compute the current from the measured drop and from an assumed resistance of the included pipe length. The methods which Dr. Hering gives in his paper for measuring pipe currents involve essentially the actual measurement of the resistance of a length of pipe, which is part of a piping system. These methods are in fact special cases of a general method based on Kirchhoff´s first law, namely, that the sum of the currents flowing towards a junction point is equal to those flowing away from the point. This principle has been used before for measuring pipe resistances, and is mentioned on page 67 of the American edition of Dr. Michalke´s book on “Stray Currents from Electric Railways” published in 1906. For a number of years I have also used in special cases what is practically the last modification of the method described by Dr. Hering in the second paragraph of page 1156. In carrying out the method I have used the connections shown in Fig. 1 of this discussion.