In a paper given last year1 there are presented formulas for the attenuation of forced drainage currents and voltages to earth along a long uniform leaky structure. These formulas treat the situation where the forced drainage is applied at a single point or at points sufficiently separated so that there is no interaction between the drains. Frequently, forced drainage is applied at more or less regular intervals along a structure to order to provide more uniform cathodic protection and to avoid, as far as practicable, excessive negative potentials to earth near the drainage points.
The spacing of drainage points and the current drained at each point depend in large measure on practical considerations such as, ease of installing low-resistance grounds, proximity to power sources, right-of-way questions, etc:
In preliminary studies, however, it is convenient to be able to estimate from test data the effects that may be expected per...
