Grounding is an important technological process that protects a person from accidental electric shock while operating household appliances or electrical appliances. To replace the wiring, repair it or modernize it, you first need to familiarize yourself with the grounding system that is used in a particular building structure. At the end of the work, the safety of households, as well as the operation of the equipment, will depend on this.
Classification of grounding systems
There are several types of grounding systems that were developed by the International Electrotechnical Commission and adopted by the State Standard of the Russian Federation. All of them are listed and described in detail in the "Electrical Installation Rules" (PUE).
- TN system and three subspecies;
- TT system;
- IT system.
Their main difference lies in the source of electricity used, as well as the methods of grounding electrical appliances. The classifications of grounding systems are designated by letters according to a certain principle.
By the first letter, it is possible to determine how the power supply is grounded:
- T - direct connection of the neutral working conductor of the power source (neutral) to the ground.
- I - in this case, the neutral of the power source is connected to the ground exclusively through the resistance.
The second letter in the abbreviation indicates grounding in conductive exposed parts of a building:
- T - indicates separate (local) grounding of the power source and electrical appliances.
- N - the power source is grounded, but consumers are grounded only through the PEN conductor.
The letter N defines a functional method, the essence of the implementation of which lies in the device of zero protective and zero working conductors:
- C - the functions of both conductors operate thanks to a common conductor called PEN.
- S - indicates that the working neutral conductor (N) and protective (PE) are separate.
Grounding systems are also divided into working and protective. The first is intended for the safe and efficient operation of all electrical devices, the essence of the latter is to ensure complete safety during the operation of these devices.
Voltage and current values can reach critical levels only for two reasons - improper use of equipment and lightning strike.
Natural and artificial types of grounding
The following are used as natural protection:
- Lead cable sheaths laid in underground trenches; rail tracks of non-electrified sidings, railways, etc.
- Reinforced concrete and metal structures of any building structures that are in direct contact with the ground.
- Underground water and sewerage lines. Do not use metal pipes through which explosive and flammable substances pass.
As a rule, horizontal and vertical electrodes are used for artificial ground electrodes. The role of vertical ones can be played by a rod or a steel pipe, at least 3 meters long.The essence of the implementation is to immerse the upper ends in the ground and connect with a strip of steel using a welding machine. This technology forms a ground loop.
For the safe use of electrical appliances, natural grounding conductors must be used. Their use saves the family budget and time, since there is no need to build artificial ground electrodes. If the natural species meets all the requirements of the PUE for spreading resistance, an artificial one can be omitted.
Comparison of artificial and natural contour
The natural contour is two or more metal structures that are in contact with the soil for the safe use of household appliances. Natural grounding is also divided into the following types:
- Pipelines for various purposes, buried in the ground.
- Reinforcement of building structures, which is immersed in soil layers.
These types of protective contour must be connected to the object with at least two elements. As a rule, they are installed in different parts of the structure.
It is prohibited to use as natural protection:
- heating systems and sewerage lines;
- pipes, the surface of which is coated with an anti-corrosion compound;
Artificial ground electrode - metal structures intended for the transportation of flammable and toxic substances.
An artificial contour is a special structure made of metal. For work, they are immersed in soil layers. The most common examples of artificial safety circuits are:
- Metal sheets embedded in the ground. They can be characterized by different shapes and sizes.
- Bars, angles, pipes and steel beams placed in the ground.
Each element of the artificial circuit must necessarily have corrosion-resistant electrical conductors made of zinc or copper.
Types of artificial grounding
The main regulatory document in Russia that allows the use of different grounding systems is PUE, clause 1.7. It was developed taking into account the methods of arrangement of grounding systems, their classification and principles. The document was approved by a special protocol of the International Electrotechnical Commission.
The abbreviated names of existing systems are combinations of the first letters of French words.
- T - grounding.
- N - connection to neutral.
- I - isolation.
- C - connection of the working and protective neutral conductors in one wire.
- S - separate use of protective and working neutral conductors.
To understand what the differences are and how they are implemented, you need to familiarize yourself with each variety in more detail.
TN earthing device
To implement the method, it is required to technologically drive a group of pins into the ground in a vertical position so that the depth is at least 2.5 meters. All pins must be connected to each other using a cable and a strip to form a single contour of a residential building.
TN-C system
Today, this type carries a potential hazard, since it does not have a single separate conductor.If, in an emergency or abnormal situation, the neutral wire is cut off, the entire electrical potential is concentrated on the devices, and this already poses a danger to human health and life, there is a likelihood of a fire.
TN-S system
A new grounding system is used in the new buildings under design. The essence of its implementation lies in the presence of a separate phase wire, neutral and protective conductor. PE and N conductors are separate components of the power supply system.
Of the accepted and approved methods of grounding the electrical network, the TN-S system is considered the safest and most reliable. Among the disadvantages should be highlighted the high cost.
Earthing system TN-C-S
This grounding system has incorporated the best qualities of its predecessors and partially eliminated their disadvantages. The method is relatively simple to implement, another advantage of the view is that it can be implemented during the reconstruction and modernization of outdated buildings. The point is the organization of the TN-C system, here the neutral wire is divided into two conductors N and PE, then the TN-S method begins to be implemented.
However, the problem of the protective circuit of the TN-C system has not yet been resolved. If the bus breaks, all electrical potential is concentrated on the household appliances. It is possible to deal with this drawback with the help of auxiliary structures, for example, a voltage relay, which is able to automatically conduct an emergency disconnection of devices from the network.
Functional grounding type TT
Functional grounding is used in those conditions when it is simply impossible to organize a grounding circuit of the TN type. The essence of the implementation lies in two separated grounding devices. Most often used when laying overhead power lines. It is also used in case of an emergency condition of neutral conductors.
The peculiarity of protecting a person from electric shock lies in the mandatory installation and use of a residual current device with a differential current of no more than 30 mA.
IT grounding scheme
Only the neutral of the transformer is grounded with the help of instrumentation, which performs the function of protection against electrical leakage. If the devices catch excess power consumption, the devices will shut down.
The main purpose of grounding is to make the use of electrical appliances safe, as well as to extend their service life. You should not neglect the design and construction of grounding, this is an unjustified risk.
