Stray currents are a type of directed motion of charged particles that occurs in the earth when the latter is used as a conductor. The main danger of this phenomenon is the development of corrosion of metal objects that are underground or at least partially in contact with it.
Stray currents occur when several metal parts (while the metals must be heterogeneous), between which there is contact, are placed in some kind of electrolytic liquid. This liquid can be absolutely everything except distilled water. Moreover, with increasing temperature, the electrolyte conductivity will only increase, as, for example, happens with ships that move from the northern seas to tropical countries.
Stray currents can occur under the influence of both internal and external sources, such as, for example, a short circuit in the electrical network, improper connection of elements, poor insulation of wiring. As for large building structures, which can be attributed to any multi-apartment residential building, then a stray current is generated in them due to the fact that a potential difference is formed between the grounding elements in different parts of the building.
As you know, any metal structure must be closed to the neutral conductor in the input-distribution device. Such a system is called the potential equalization system, it is necessary so that there is no directed electric current between the grounding elements.
Another important reason for the formation of stray currents and, as a result, electrochemical corrosion, is the widespread replacement of metal pipes with plastic pipes in apartments. The thing is that in this case the metal connection is broken between the main risers, which are grounded through the potential equalization system, and additional pipes that lead, for example, to a heated towel rail. In this case, a potential difference is formed between the riser and auxiliary pipes, and if a conductor, for example, flowing water, appears between them, an electric current arises.
Protection against stray currents consists in equalizing potentials between metal structures. To do this, it is enough to connect the main riser and auxiliary pipes, after which the possibility for the appearance of electric current will disappear.
Another danger is connected with the fact that water moving through pipes, which, as was mentioned above, is an excellent conductor, is constantly in contact with the pipes themselves - dielectrics. From this friction an electric current arises , which, in accordance with the basic physical laws, will accumulate at the ends of the metal structures. The resulting static charge will play an important role in the fact that the emerging stray currents will have greater strength. This must be taken into account.
Thus, stray currents are a fairly common phenomenon in everyday life. To avoid their unpleasant effects, it is necessary to carefully approach the grounding of all metal structures in the house, especially considering that some of the pipes are now being replaced with metal-plastic ones.