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return current is not entirely removed from the earth, such action will continue.
5. The extent of the electrolytic injury at any point is directly proportionate to the number of amperes leaving the pipe. The smallest measurable difference of potential is sufficient to produce electrolysis,
8. A cast iron water main is not a continuous electric conductor; and its joints offer very much higher resistance than an equal length of the plain pipe.
7. The inevitable effect of any resistance at the joints is to cause a part of the current carried on the pipes to be shunted around the joint, either through the soil on the outside or through the water on the inside, or by both paths.
8. Wherever the current leaves the pipe to pass around the joint, either outside or inside, or both, the pipe is injured. The action of the fraction of an ampere flowing around successive joints will in time do great aggregate damage to any cast iron main on which it flows.
Your committee is convinced after careful consideration of reliable data of the subject, that there is no known practical method by which owners of underground pipes can protect them against electrolytic injury from single trolley currents; but that there are two methods of operating electric railways by which the return currents can be kept out of the ground, namely, the conduit system, as in use in New York City and in Washington (D.C.) and the double overhead trolley system, as operated in Cincinnati (Ohio), and on suburban lines in the District of Columbia.
The
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return current is not entirely removed from the earth, such
action will continue.
5. The extent of the electrolytic injury at any point is directly proportionate to the number of amperes leaving the pipe. The smallest measurable difference of po- tential is sufficient to produce electrolysis,
8. A cast iron water main is not a continuous elec-
tric conductor; and its joints offer very much higher resis-
tance than an equal length of the plain pipe.
7. The inevitable effect of any resistance at the
joints is to cause a part of the current carried on the
pipes to be shunted around the joint, either through the
soil on the outside or through the water on the inside, or by both paths.
8. Wherever the current leaves the pipe to pass
around the joint, either outside or inside, or both, the pipe is injured. The action of the fraction of an ampere flowing around successive joints will in time do great aggregate
damage to any cast iron main on which it flows.
Your committee is convinced after careful consider-
ation of reliable data of the subject, that there is no
known practical method by which owners of underground pipes
can protect them against electrolytic injury from single
trolley currents; but that there are two methods of opera-
ting electric railways by which the return currents can be
kept out of the ground, namely, the conduit system, as in use
in New York City and in Washington (D.C.) and the double
overhead trolley system, as operated in Cincinnati (Ohio),
and on suburban lines in the district of Columbia.
The
Page 600Page 601
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