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One of the best technological ways to protect against possible electric shock when using electrical appliances is grounding.
At the moment, grounding is a whole system that is created at the stage of designing a room, and requires a serious approach when performing its installation.
To bring to a single standard, the International Electrotechnical Company has developed a classification of grounding systems that are used in the electrification of premises.
According to this standard, there are three types of systems, one of which includes an additional three subsystems.
Designation of systems, decoding
To designate each system, an alphabetic index consisting of several letters is used.
The first letter in the index indicates the nature of the grounding of the main power source of the devices (transformer substation), and the second – to the grounding of open sections of electrical installations.
For the designation, certain letters of the Latin alphabet are used, each of which has its own decoding:
- T – grounded (from “Terre” – earth);
- N – zeroed, connected to the source neutral (from “Neuter” – neutral);
- I – isolated (from “Isole” – isolation).
These three letters are used to designate grounding systems that are included in the international standard.
The three earthing systems according to IEC are designated:
- TN (which in turn is divided into subsystems TN-C, TN-S, TN-CS);
- TT;
- IT.
Additionally, the classification introduced the letter designation of neutral conductors involved in grounding systems:
- N – working;
- PE – protective;
- PEN – combined (combined), including both working and protective neutral conductors.
All of these systems have their own design features, which predetermine their scope of use.
For residential use, TN earthing subsystems are more suitable.
The TT system is applicable for mobile buildings (construction and other trailers, kiosks with metal surfaces), but IT is used mainly for organizing the grounding of laboratories.
The grounding system used in the electrification of premises must be indicated in the project documentation, since for maintenance and repair work it is necessary for the electrician to know exactly which of the systems is used.
The existing standard of the grounding system is international, so it is also used by us.
Moreover, the entire regulation that is in force with us and regarding grounding systems is fully spelled out in the rules for the installation of electrical installations (PUE). Moreover, the PUE is valid both on the territory of the Russian Federation and Ukraine.
These rules are a general provision for the correct conduct of electrification, the operation of electrical appliances and the provision of protection.
Next, we consider the features of each of the systems, as well as their advantages and disadvantages.
See also:
TN system and its subsystems, their features, advantages, disadvantages
A common feature of the TN system is that the neutral of the power supply has a dead ground (connected to a ground loop installed near the substation).
Open sections of electrical wiring are connected to this ground by means of neutral conductors.
The existing subsystems are just divided according to the method of connecting these conductors to ground.
TN-C.
The TN-C system is one of the most common types of grounding, which is currently outdated, but is often found in old houses.
It differs in that the N and PE conductors (working and protective) are combined into a single PEN conductor throughout the system.
This system is widely used due to the ease of installation and cost-effectiveness, since it does not require laying and connecting additional wires. This is its main advantage.
But this system does not provide a separate protective earth. That is, at the end point of the electrical wiring of a residential building – a socket, it is absent, which significantly reduces the safety of using electrical appliances in housing.
The PEN conductor present in the system is connected only to the electrical panels – introductory and floor.
Due to these design features, when installing new power lines, as well as reconstructing existing ones, it is forbidden to use this system.
To improve safety, zeroing is often used, which makes it possible to deal with short circuits that may occur in the network.
If a short circuit occurs, zeroing will ensure that the circuit breakers operate to turn off the power supply at home.
TN-S.
In new buildings, the TN-C system is no longer used; for them, the TN-S system is more preferable.
It is characterized by the fact that the working and protective neutral conductors are separate throughout the system. That is, the wiring includes separately N and PE conductors.
This system is distinguished by providing a high degree of human safety and protection of equipment and electrical appliances, since even the end points of the electrical network have protective earthing.
In addition, it does not generate high-frequency interference, which may occur in the first system during the use of a vacuum cleaner, drill and other electrical appliances.
The advantages of this system also include the absence of the need to periodically check the condition of the ground loop.
At the same time, the cost of laying such a system is very high. This is due to the fact that during installation work it is necessary to lay multi-core cables.
For a single-phase network, the cable must contain 3 cores (phase, working zero N and protective PE).
And for a three-phase cable, you need a 5-core cable (3 phases – A, B, C, as well as N and PE).
It is the high cost that is the main disadvantage of this system.
TN-CS.
The last subsystem – TN-CS combines the design features of the two previous systems.
Its main difference is that a PEN conductor goes from the substation to the residential building. But at a certain stage, it is divided into a working N-conductor and a protective PE-conductor.
Usually, separation is done at the input distribution device (ASU), that is, at the entrance to the house.
In this case, after separation, the PE conductor is re-grounded by connecting it to the ground loop of the house.
After splitting, separate neutral conductors are already supplied to the apartment shields, which makes it possible to create a protective ground at the end points of the network. That is, it turns out that the TN-C system goes before the ASU, and after it – already TN-S.
Such a system is quite promising for us, since it allows us to quickly and cost-effectively upgrade the TN-C system, thereby significantly increasing the safety when using household electrical appliances.
But she also has one drawback, which boils down to the fact that if the PEN conductor is damaged, the wiring is completely deprived of grounding, which can lead to electric shock, since the housings of electrical appliances may be energized.
Features of the TT system
The TT system is designed to provide grounding for buildings where it is impossible to create the necessary electrical safety conditions for the use of TN subsystems.
First of all, such a condition is the unreliability of overhead power lines and the absence of backup grounding on the supports.
TT is also used to ensure the safety of mobile buildings and buildings with conductive surfaces (kiosks, containers, trailers made of metal).
The peculiarity of this system is that the ground loops are used separately for the substation and the premises, so there are no neutral conductors between them.
In addition, in this system, no crossing between N and PE conductors is allowed. That is, each of them must have its own ground loop.
Thanks to such constructive solutions, it is possible to ensure the insulation of conductive surfaces, as well as buildings, from a possible break in the power line.
Note that when organizing a TT, it is required to use residual current devices (RCDs) for all groups of power lines in order to provide protection against accidental contact with live parts of electrical appliances, as well as for safety in the event of a current leakage in the house.
It has a high safety rating, and is great for private homes, temporary buildings, etc.
The disadvantages of TTs include the need for careful selection of protective circuit breakers and the correct calculation of their operating parameters.
In addition, there is a possibility of a simultaneous failure of the RCD and a phase breakdown on the body of the electrical appliance.
As a result, the entire line of the PE conductor and open conductive sections are energized.
IT system
The IT system is designed for use in institutions where highly sensitive devices can be used (laboratories, medical facilities).
The peculiarity of IT is that the neutral of the transformer substation is insulated with respect to the ground, or special devices and devices with high resistance are used for grounding.
But open areas of electrical installations are grounded in the classical way – through a ground loop.
The use of the IT system ensures that sensitive equipment is exposed to electromagnetic fields to a minimum.
IT IS IMPORTANT TO KNOW: How to ground a washing machine.
FAQ
Now let’s go over some of the questions people often ask about grounding homes.
Question 1: What is the best material to use when installing groundings?
This is an important question, because the health of the entire network depends on it.
Answer:
The main ones in grounding are circuits that ensure the removal of electric current and its dissipation into the ground.
To create contours, metal or copper products are used. It consists of vertical (electrodes) and horizontal (strapping) electrodes.
According to the PUE, steel rods with a diameter of 16 mm can be used as vertical electrodes.
Or corners with a section of 100 mm and a thickness of at least 4 mm.
Steel pipes with a diameter of 32 mm, with walls of at least 3,5 mm, are also suitable.
If the material for the manufacture of electrodes is copper, then you can use rods with a diameter of 12 mm, pipes – 20 mm.
For strapping, steel rods of 10 mm or a tape with a cross section of 100 mm are suitable.
As for copper, in addition to rods and pipes for strapping, you can use a copper stranded cable with a cross section of at least 35 mm.
As for conductors, copper wires with a cross section of at least 10 mm and aluminum wires of at least 16 mm should be used to organize N and PEN conductors.
Read more here – how to make grounding in a private house.
Question 2: How to recognize which system is used in the house?
Answer:
If it is not possible to find out in the technical documentation which of the systems is used in the house, then you can recognize it by certain signs.
You should look at the introductory wiring in the ASU. If, with a single-phase network, 2 wires are suitable for the ASU or 4 – with a three-phase network, then this indicates the use of TN-C or TN-CS.
Next, you should consider the PEN-wire connection terminal, if the wiring is separated on it, that is, after entering the apartments, N and PE-conductors go separately, then this indicates the use of a TN-CS system.
If the number of incoming wires is 1 more (single-phase – 3 wires, and three-phase – 5 wires), this means that the TN-S system is installed in the house.
Question 3: If the house has a TN-C system, can it be upgraded?
Answer:
It is quite possible to convert TN-C to a more modern one. And for this it is better to use TN-CS.
In this case, it will not be necessary to change the neutral conductor in the section from the substation to the ASU.
To finalize the existing system, it will be enough to install an additional wire from the ASU to the switchboard, as well as to split the PEN conductor into N and PE.
The laid wire will play the role of a protective conductor (PE). It is important only after splitting it to be additionally grounded.
It is important to know: How to properly install electrical wiring in a wooden house.
But remember, system upgrades should only be carried out by qualified specialists. Electricity is no joke.