In the great majority of cases, the danger of corrosion for underground installations {water, steam, gas piping, etc.} is caused by direct current escaping from the main d. c. network. Such main networks are the systems of city streetcars and electrified railroads as well as grounded electrical distribution points and industrial power plants. In streetcar systems, current from the positive pole of the source is connected to the feeding line from which it is picked up by the streetcar. After performing its work, the current proceeds to the rails from which it goes to the drainage point where the receiving feeder leading the current to the negative pole of the source is connected. Owing to the insufficient conductivity of the rails, part of the current goes into the ground and proceeds through it over a certain distance before returning to the rails at the receiving feeder. In the ground, the current moves along the path of the least resistance through various metallic underground installations.