Grounding of electrical installations is divided into two main types - functional working and protective. In some sources, there are additional types of grounding, such as measuring, control, instrumental and radio.
Working or functional grounding
In the PUE section in paragraph No. 1.7.30, the definition of working grounding is given: "a worker refers to the grounding of one or more points of current-carrying parts of an electrical installation, which does not serve for safety purposes."
Such grounding involves electrical contact with the ground. It is necessary for the normal operation of the installation in normal mode.
Functional grounding purpose
In order to understand what is called working grounding, you should know its main purpose - to eliminate the danger of electric shock in the event of a person touching the body of the electrical installation or its live parts that are currently under voltage.
Such protection is used in networks with a three-phase current distribution system. An isolated neutral is necessary for the mains, where the voltage does not exceed 1 kV. In networks with voltages above 1 kV, protective grounding can be done with any neutral mode.
How protective (functional) grounding works
The principle of the functional grounding is to reduce the voltage between the case, which, as a result of an unforeseen accident, is under current, and the earth to a value safe for humans.
If the housing of the electrical installation, which is under current, is not equipped with functional grounding, then touching a person to it is equivalent to contact with a phase wire.
If we take into account that the resistance of the shoes of a person who touched the electrical installation and the floor on which he stands is negligible relative to the ground, then the current can reach a dangerous value.
With the proper functioning of the functional grounding, the current passing through a person will be safe. Touch voltage will also be negligible. Most of the electricity will go through the ground conductor to the ground.
Differences between working and protective earths
Working and protective grounding differs from each other primarily by purpose. If the first is necessary to ensure the correct and uninterrupted operation of electrical equipment, the second serves to protect people from electric shock. It also protects equipment from breakdowns in the event of a breakdown of an electrical device on the case. If the building is equipped with a lightning rod, this type of grounding will protect the devices from overload in the event of a lightning strike.
Working grounding of electrical installations, in the event of an emergency, will play a protective role, but its main function is to ensure the correct uninterrupted operation of electrical equipment.
Unchanged, functional grounding is used only at industrial facilities. In residential buildings, a grounding conductor is used, which is connected to a power outlet. However, there are household appliances in the house that pose a potential danger to the consumer, so it will not be superfluous to ground them using a grounded neutral.
Home appliances that need to be connected to a working ground:
- Microwave
- Oven and stove, which work due to electricity.
- Washer.
- The system unit of a personal computer.
Grounding design
Working grounding consists of iron pins driven into the ground, playing the role of conductors, to a depth of about 2-3 meters.
Such metal rods connect the grounding terminals of the electrical equipment to the grounding bus, thereby forming a metal connection.
There is a metal connection in every apartment building. This is a welded iron structure that connects the upper ends of the ground electrodes to each other. She is taken to the entrance shield of the house for further wiring in apartments.
As a grounding conductor, use a bus or wire with a cross section of at least 4 square meters. mm, painted in yellow and green stripes. The cable is mainly used to transfer functional grounding from bus to bus.
For safety reasons, a periodic check of the electronic resistance of the metal ground connection is carried out. It is measured from the ground terminal of the electrical installation to the most distant ground ground loop. The resistance index in any part of the working ground should not exceed 0.1 ohms.
Why do several grounding conductors
The electrical installation cannot be equipped with only one ground electrode, since the soil is a non-linear conductor. Earth resistance is highly dependent on voltage and contact area with the stuck pins of the working ground. One ground electrode system will have insufficient contact area with the soil to ensure uninterrupted operation of the electrical installation. If you install 2 earthing switches at a distance of several meters from each other, then there is a sufficient area of contact with the ground. However, it should be remembered that the metal parts of the grounding cannot be carried too far, since the connection between them will be interrupted. As a result, there will remain only two ground electrodes separately installed in the soil, not connected in any way with each other. The optimum distance between two ground loops is 1-2 meters.
How to ground
According to paragraph 1.7.110 of the EMP, it is forbidden to use any kind of pipelines as a working ground. In addition, it is forbidden to bring the grounding cable out and connect it to an unprepared contact area on the bus. Such a ban is explained by the fact that each metal has its own individual potential. When exposed to external factors, galvanic steam is formed, which contributes to the process of electroerosion. Corrosion can spread under the sheath of the grounding wire, which increases the risk of its melting during the supply of large currents to the ground loop in the event of an accident. Special protective grease prevents the destruction of the metal, but it acts only in a dry room.
The PUE also prohibits alternating grounding of electrical installations with each other, and connecting more than one cable to one grounding busbar ground. If these rules are neglected, then in the event of an accident at one installation, it will interfere with the work of a neighbor. This phenomenon is called electrical incompatibility. If the working earthing is improperly connected, corrective work is life threatening.
Grounding Requirements
To understand what is called working grounding, as well as what requirements are imposed on such structures, you should know that to protect people from electric shock, the voltage of which does not exceed 1000 V, it is necessary to ground absolutely all metal parts of electrical equipment. It is important that all structures constructed for grounding purposes comply with all safety standards required to ensure the normal operation of networks and additional fuses against possible overload.
Risk of contact with live parts
If a person comes in contact with live parts of an electric circuit or with metal structures that are energized as a result of a violation of the cable insulation layer, electric shock may occur. The resulting injury manifests itself in the form of a burn on the skin. From such a blow, a person can lose consciousness, it is possible to stop breathing and heart. There are cases when an electric shock at low voltage leads to the death of a person.
Electric Shock Precautions
In order to maximally protect people from contact with live parts of the electrical installation, as well as with its metal parts, it is necessary to completely isolate the hazardous object. For this, various fences are installed around electrical installations.