Grounding is a set of measures aimed at connecting live parts of electrical appliances to the ground electrode. This non-troublesome process allows you to ensure the potential of the earth on the housings of household appliances to prevent electric shock when touching the housings of devices, as well as other parts of damaged equipment. Connection to the grounding bus is by cable or wire.
Why do you need a ground wire, the principle of operation
The main purpose of grounding is to prevent electric shock to a person or animal. A working electrical appliance has a complete housing with reliably insulated live parts. If household appliances fail, live parts may touch the housing and this will cause it to be live too. Touching such a device, a person will inevitably be shocked.
In this case, the operation of the circuit breaker is impractical, since the current flowing through the human body will not be enough to turn off the power supply. But this force, unfortunately, is enough to deprive a person of health or even life.
To eliminate the likelihood of such events, it is necessary to ground all electrical devices through conductors. Grounding household appliances at home is only possible if the house is equipped with an earth loop. Unfortunately, the houses of old buildings are not equipped with such innovations. This is due to the fact that as early as decades ago, people in houses had practically no household appliances, therefore, the load on the network was minimal.
Now, another wire is added to the two-phase wiring - the ground wire. As a result, the wiring is already three-phase - two wires are zero and phase, and the third is protective earth. Thus, by connecting the plug of household appliances to the outlet, the metal case of the device automatically connects to protective ground.
Criteria for choosing a grounding cable
Before choosing a grounding conductor, you need to deal with several important points.
Owners of private houses and suburban buildings in 1998 and earlier had to independently carry out grounding. Modern structures are still being equipped with a ready-made system during the construction process.
To correctly select the ground wire and its cross section, you need to find out which system is installed in the house. According to the Electrical Installation Rules, 4 types of them can be used:
- TN-S - in the AC system, an additional grounding is made using neutral and a separate wire.
- TN-C is characterized by a combination of zero and ground wires, the neutral is output separately. The most common protection method used in Europe several decades ago.
- TT - equipping electrical equipment with direct protective grounding.
- IT - work directly with housings of household appliances through the complete isolation of all conductive cables and the housing itself.
The earthing diagram used must always bear the marking. In Russia, there are two of them:
- PE - grounding;
- PEN - zero and ground are combined in one cable.
The next important selection criterion is the type of grounding used. Depending on the purpose, they are divided into two types - portable and stationary.In domestic conditions, a stationary type is sufficient, which allows the operation of both single-core and three-core cables.
Many of the uninformed people in these surveys have difficulties in what color the ground wire is. According to the requirements of the PUE, the wire must be made in yellow-green color insulation.
After determining the type of cable and the material of the system, you can proceed to the next main step - the selection of a suitable section.
How to choose the cross section of the grounding conductor
To connect the protection system, not only natural grounding conductors, but also artificial ones can be used. The selection rules in each case differ from each other and have their own technical features.
Networks with a capacity of more than 1 kW are equipped with artificial ones; in other cases, exploitation of natural ones is permissible.
The artificial segment is made of galvanized alloys, steel and copper. The section is selected according to the Electrical Installation Rules in the special tables.
| Material | Section profile | Diameter (mm) / cross-sectional area (mm.kv) |
| Copper |
|
|
| Galvanized steel |
|
|
| Black steel |
|
|
One simple but important rule - the conductor must have a cross section that is equal to the cross section of the phase wire, provided that the conductor is at least 16 mm.sq. In other cases, the cross section is calculated using the table given in the PUE.
| Section of phase conductors, mm.kv. | The smallest section of protected conductors, mm.kv. |
| S> 35 | S / 2 |
| 35> S> 16 | 16 |
| S <16 | S |
In an ordinary apartment, which is equipped with all necessary equipment, it is enough to install a protection system with a single-wire cable with yellow-green insulation.
Wire marking
Grounding wires have another characteristic feature - marking.
Ground color
Grounding, according to the rules of the PUE, should be painted in yellow-green color. However, light green or completely yellow wires are rare. Also, the cable can be equipped with a blue braid at the fixation points, which indicates grounding along with zero.
In the distribution panel, it is connected to a bus, a housing and a shield door made of metal. In the box, the connection tends to earth wires. The ground conductor must not be connected to a residual current device.
Symbols on electrical circuits: for direct current, standard grounding, to the body of electrical equipment, clean and protective.
Neutral color
The zero conductor has a strictly blue color. In the distribution panel, it must be connected to the neutral bus, which is indicated by the letter N. All the remaining blue conductors are connected to it. Through the electric meter or directly without installing the machine, the bus is connected to the input. In the junction box, all wires, with the exception of blue, should not be involved in switching. Zero conductors in sockets are connected to a contact, denoted by N - located on its back side.
Phase color
Compared to ground and neutral, the phase has a wider range of colors. Any color other than blue, yellow, and green can be used to indicate wires. The most common are black, red and brown.
In the junction box, the phase that moves away from the consumer is connected to the contact of the automatic switch located at the very bottom, or the residual current circuit breaker. The switches carry out phase switching.
Self marking wires
From time to time, conductors with unusual colors are found. Such decisions do not comply with the standards set out in the EMP. To facilitate the task, it is recommended to independently mark the wires with the necessary colors. Used for this colored tape, as well as heat shrink tube.
Another task of the wizard is to write separately on the leaflet the color values.
The main brands of grounding cable
When choosing a brand of cable, it is necessary to study its type: mobile or stationary use. Stationary is designed to protect equipment, switchboards and structures. The best option is multicore multi-wire cables (VVG, PVG) and single-wire modifications (NYM). If the ground cable is colorless, ground is directed towards the core.
- NYM cable - sheath is painted in accordance with all the rules and regulations, inside is equipped with copper conductors. It also has an intermediate additional sheath, which increases the operational life of the cable even with prolonged use. It does not cause installation difficulties.
- VVg - equipped with cores made of copper of the first and second twisting class. It has an unusual color, which is worth paying attention to. Earth is yellow-green and zero is blue. The outer sheath and insulation are made of polyvinyl chloride, so the cable will not burn even in case of fire.
- PV-6 is a copper wire, the sheath is made of transparent PVC. There is an opportunity to contemplate the work of a conductive core. Operating temperature range -40 - +50 degrees Celsius, very flexible material.
- ESUY has one standard application - system short circuit protection. Able to withstand enormous loads, often used in junction boxes and on railways.
- PV-3 can be produced in 11 colors, consists of a large number of copper filaments, which are placed in a polyvinyl chloride shell. A feature of the outer shell is fragility upon improper storage or use.
The issue of choosing a grounding cable is extremely important, since an incorrectly selected core will be unable to fulfill all the technical tasks assigned to it. If there are difficulties with independent choice, it is better to consult a specialist.
