Система TN-C - TN-C system
When designing, installing, and operating electrical installations, industrial and household electrical equipment as well as electrical illumination grids, one of the basic factors to provide their functionality and electrical safety is accurately designed and properly made grounding. Key requirements to the grounding systems are provided in item 1.7 of the Electrical Installations Code (EIC). Depending on how and with what grounding structures, devices, or objects the respective wires, devices, device enclosures, equipment or particular grid points are connected, natural or artificial grounding is distinguished.
Natural grounding arrangements are represented by any metal objects permanently laid in the ground: piles, pipes, reinforcement and other current conducting items. However, due to the fact that the electrical resistance to the current flowing in the ground and electrical charges from such objects can be hardly controlled and predicted, it is prohibited to use natural grounding when operating the electrical equipment. The regulatory documentation provides for the use of artificial grounding only, wherein all connections are made to the special grounding devices.
Resistance is a basic standardized indicator characterizing how well the grounding is. Here, the resistance to the current flow entering the ground from this device, i.e. grounding electrode, is controlled. The grounding resistance depends on the soil type and condition as well as on the specifics of the structure and materials from which the grounding electrode is made of. A determining factor that impacts the grounding resistance is an area of immediate contact with the ground of plates, rods, pipes, and other electrodes being a part of it.
The main document regulating the use of various grounding systems in Russia is the EIC (item 1.7) developed according to the principles, classification, and methods for the arrangement of grounding systems, which are approved by a special protocol of the International Electrotechnical Commission (IEC). The abbreviated grounding names are taken from first letters of the French words: Terre means ground, Neuter means neutral, Isole means isolate, as well as English words: combined and separated.
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