What does tn-c-s system refer to?

tn-c-s system refers to the temporary power supply of the power supply system during building construction. If the first part is powered by "TN-C" mode, and the construction specifications stipulate that the construction site must use the "TN-S" mode power supply system , then the PE line can be branched out from the main on-site distribution box at the rear of the system.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

TN-C-S mode power supply system In the temporary power supply during building construction, if the front part is powered by TN-C mode, and the construction specifications stipulate that the construction site must adopt a TN-S mode power supply system, then the rear part of the system can be used. The on-site main distribution box branches out the PE line. The characteristics of the TN-C-S system are as follows.

1) The working neutral line N is connected to the special protection line PE. When the unbalanced current of the line is relatively large, the zero connection protection of the electrical equipment is affected by the neutral line potential. There is no current on the line from point D to the rear PE line, that is, there is no voltage drop on this section of wire. Therefore, the TN-C-S system can reduce the voltage of the motor shell to the ground, but it cannot completely eliminate this voltage. The size of this voltage depends on the ND line. The load unbalanced situation and the length of the ND line. The more unbalanced the load is and the longer the ND line is, the greater the voltage offset between the equipment shell and ground will be. Therefore, it is required that the load unbalanced current should not be too large, and the PE line should be repeatedly grounded.

2) The PE line cannot enter the leakage protector under any circumstances, because the action of the leakage protector at the end of the line will cause the front-stage leakage protector to trip and cause a large-scale power outage.

3) Except for the PE line which must be connected to the N line at the main box, the N line and the PE line are not allowed to be connected at any other sub-box. No switches or fuses are allowed to be installed on the PE line. It is also not allowed to use the earth as a PE line.

Through the above analysis, the TN-C-S power supply system is a temporary modification to the TN-C system. When the three-phase power transformer is in good grounding condition and the three-phase load is relatively balanced, the TN-C-S system is still feasible in construction power practice. However, when the three-phase load is unbalanced and there is a dedicated power transformer at the construction site, the TN-S power supply system must be used.

Extended information

1. In the power supply mode symbols specified by the International Electrotechnical Commission (IEC), the first letter indicates electricity (Power supply) system to ground relationship. For example, T means that the neutral point is directly grounded; I means that the power supply is isolated from the earth or that one point of the power supply is connected to the earth through high impedance (for example, 1000Ω;) (I is the first letter of the French word "Isolation").

2. The second letter indicates the relationship between the exposed conductive part of the electrical device and the ground. For example, T indicates that the equipment shell is grounded, which has no direct relationship with any other grounding point in the system; N indicates that the load adopts zero-connection protection.

3. The third letter indicates the combined relationship between the working zero line and the protection line. For example, C means that the working neutral line and the protection line are integrated, such as TN-C; S means that the working neutral line and the protection line are strictly separated, so the PE line is called a dedicated protection line, such as TN-S.

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