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In-depth Knowledge of Low-voltage Network Earthing System

Posted: 06/04/2016 04:32:20  Hits: 563
The earthing system of low-voltage network can be divided into three categories - TN, IT and TT, TN is subdivided into TN-S, TN-C and TN-C-S. These earthing systems can be interpreted authentically as IEC60364 series standard and GB16895 series standard. The former is IEC (International Electrotechnical Commission) standard, latter is Chinese national standard, the two different standard can be used equally.

In the first place, we should get clear about a conceptual framework that the personal safety protection at the time of using electricity.

There are two theories for protecting personal safety, one is direct and rigid isolation, the other is indirect isolation. 
Earthing system belongs to indirect isolation.Personal safeguard procedures can be stipulated by two more norms, that are IEC60354 and GB16895, they are to some extent equal.

About direct isolation and indirect isolation:
Direct isolation, it adopts quarantine measures. For instance, segregating the appliances and put them into distribution box or a cabinet, add a guard outside of them. But it’s worth noting that the safeguard procedures of distribution box and cabinet not only prevent from people but also fine dust and vapour aqueous which we call it IP level of protection. 

Higher level protection, better effect it would be. However, high protection level is not beneficial for volatilizing heating, higher level would lead to poorer heating dissipation, here is a contradiction. Thus, when we order the electrical equipment, be attention to choose appropriate protection level on the basis of reality (environmental average temperature, humidity, altitude, fine dust containing).

The voltage of low-voltage distribution system refers to 1000V and its’ following voltage classes.

Here are two types fundamental connections of low-voltage network ground connection:
The first connection is the conductor or electrical equipment shell of low-voltage network loop connected to the ground; 
Second, the equipotential grounding connection of low-voltage network is combined with one replacing terrestrial conductor, which means the system regards this conductor potential as a reference instead of the grounding potential.

For example, the shell and framework of low-voltage switch-gear could be used as a kind of ground connector to defend therein the equipment, and the shell of low-voltage switch-gear is the reference in potential.

Earthing System 
Earthing system is the energized conductor of power supply end connected to the ground in low-voltage network, the supply of low-voltage network usually indicates transformer, electric generator or other more neutral ground connections.