Measuring stray currents in underground pipes

The measurement of stray electric currents flowing through buried conductors, such as pipes, and generally originating from an electric railroad or other grounded system of electric distribution, is attended with various difficulties, particularly in the determination of the current which enters or leaves the underground pipe through the surrounding earth, and as it is the current which leaves a pipe in this way that corrodes it electrolytically it becomes important to be able to locate and measure that current. Another important measurement is to identify the original source of the stray current.