Paper 127 of the Bureau of Standards, entitled " Leakage Resistance of Electric Railway Roadbeds and its Relation to Electrolysis," by E. R. Shepard, Electrical Engineer, gives the result of more than three years of electrical resistance measurements on different types of roadbeds.
Electrolytic damage to underground piping systems is caused from the escape of current from the rails of electric lines and the resistance of the roadbed is an important factor in, the amount of current which may escape.
Short sections of fourteen common types of roadbeds were constructed on the grounds of the Bureau of Standards and resistance measurements under varying weather conditions were carried on for a period of three years.
Some measurements were also made on a number of city lines in and about Washington, both open track and several types of roadbed in paved streets being investigated.
Through the cooperation of the United States Forest Products Laborat;ory' at Madison, Wisconsin, measurements were also made on several sections of test track on the Chicago, Milwaukee and St. Paul Railway where railroad ties subjected to several different kinds of preservatives were employed.
The results of these measurements are given in tabular and graphical form, and the following conclusions have been drawn : I. Roadbeds constructed with solid concrete ballast and vitrified brick or other non-porous pavements have a low leakage resistance to earth which is affected only moderately by seasonal and weather changes.
There is little difference between wood and steel ties in their effect on the resistance of roadbeds of this kind. Insulation is not of practical value in reducing leakage current from such roadbeds.
The resistance of single roadbed of this type is from 0.2 to 0.5 ohm per IOOO feet, under ordinary conditions, but may be two or three times this when the ballast is frozen to a depth of I foot or more. For double roadbed of this type the resistance is approximately 70 per cent. of that for single roadbed, or the leakage from double track would be about "40 to 50 per cent. greater than from single track.
'Technical Paper No. 127.