The main types of grounding systems

We have already written about grounding: about what it is and how to do it, about proper grounding connection and advice on home ground. Forum member "Home and cottage» _KM_ offers to get acquainted with the varieties of systems and the peculiarities of their use.

TN-C

For this dangerous old system of the Soviet era is characterized by the following: to the earth electrode, which is located at a substation neutral wire is connected, also acts as a protective (PEN). Because of this protection, made under the scheme, often referred to as "zeroing." Wiring make two four-wire, grounding receptacles in no contacts.

The main advantage of the system TN-C is the simplicity and low cost. The main drawback, which possess these types of ground - possible electric shock to persons: safety devices to protect the network against over-current short circuit protection, but not the people.

Inclusion of modern electrical switching power supply with a power outlet with TN-C leads to the phenomenon of removal of stress to the body. This is caused by switching power supplies which have symmetrical inlet filter impulse noise to a midpoint attached to the housing. When Vanishing 220V voltage divided by the filter device and the housing shoulders is 110V.

In rural areas, in the absence of re-grounding possible burning-off of the zero output on the power supply transformer. Depending on the connected load, the voltage on the three phases in unpredictable ways warps, which leads to a failure of all electrical household appliances.

Our comments today Type TN - C is not used in the construction of new buildings or renovation of old.

Power consumers in old buildings recommend to move from system to TN-C TN-C-S, i.e., on the introduction of building re grounded neutral, followed by separation on a wire PEN N (working zero) and PE (protective). To do this, you must make a separate focus grounding and replace all the wiring in the house. If for some reason you can not follow the letter of the instructions, you should at least ensure that the vanishing of electrical devices. Grounding screws and stationary electrical terminals need to be connected to the neutral conductor. For portable devices and appliances are three-pole socket outlets, which are also attached to the neutral wire.

It must be remembered that without these measures in the wiring to the TN-C system is safe to use only equipment with double insulation and housing parts conducting current.

TN-S

In this modern system protective earthing conductor PE and neutral N working separately are laid over the entire length with three-five conductor wires and cables. The use of such a system can prevent an electric shock (used machines and differential tripping device). In addition, the wiring on the TN-S can be used without any risk of electrical consumers with a metal frame.

Among the shortcomings of the system can call for the higher costs: necessary wires and cables with additional living and a separate center ground. Note that protect people against electric shock is possible only by using protective devices are not cheap and Emergency circuit breakers. When using a TN-S needs a qualitative and tidy wiring.

The main drawback of the system - the inability to take full advantage of this system due to the fact that the 0.4 kV distribution network in Russia made four- lines.

Eliminate this contradiction allows us to combine the grounding system.

TN-C-S

In this system, the protective conductor and the working zero before entering the building are combined (PEN), on re-entering grounded, whereupon they are divided into PE and N.

System TN-C-S is recommended for newly constructed and renovated buildings and buildings.

It should be remembered that modern electrical devices provide connectivity to networks with TN-C-S (TN-S), and not initially neutral earthing, i.e. their metal housings and parts are not connected with feeding conductors. Therefore, such devices can be connected to the network only three or five-wire cables and wires to the grounding connection terminals (bolt contact) with the grounding contact in the plug.

It is interesting that many of the old domestic devices characterized by a rigid connection housing with zero. When connecting such devices to a network TN-C-S (TN-S) can be switched off leakage current protection.

When applying the system TN-C-S must provide reliable repeated zazemenie also necessary to ground all conductive parts and the building structure.

To this end, on entering the building organize the so-called main grounding bus, ie terminals. It is connected to the ground again at home and connected thereto conductors indissoluble metal elements and structure: reinforcing cage, pipes, metal bars, profiles, etc.

Advantages and disadvantages of TN-C-S - are the same as in TN-S.

TT

This earth system differs from the previous ones in that each individual electrical device need grounding conductive housing. Ground zero of the transformer may not be as of zero (previously common its connections under the scheme "triangle", which is now used in high distribution networks).

TT option is not commonly used in electrical installations of residential buildings. The scheme should be of interest to individual developers in the event that there is no own Ground hearth to enter the building and the need to organize its electrical power from, say, gasoline generator.

However, it should be remembered that, in addition to the frame of the generator to earth ground must connect one of output terminals - the application of single-phase generator, the output of the middle point - for three-phase.

The IT system rarely used. It is used in electrical installations and buildings of special buildings, which are increased requirements security and require high potential reliability (in hospitals for emergency lighting and electricity).

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