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, a definition of working grounding is given: “working is the grounding of one or more points of the current-carrying parts of an electrical installation, which is not for safety purposes.”
Such grounding implies electrical contact with the ground. It is necessary for the normal operation of the electrical installation in normal mode.
Assignment of functional grounding
In order to understand what is called working grounding, you should know its main purpose - to eliminate the danger of electric shock if a person comes into contact with the body of the electrical installation or its current-carrying parts, which are currently energized.
This protection is used in networks with a three-phase current distribution system. An isolated neutral is required forelectrical networks where the voltage does not exceed 1 kV. In networks with voltages over 1 kV, protective grounding can be done with any neutral mode.
How protective (functional) grounding works
The principle of operation of functional grounding is to reduce the voltage between the body, which, as a result of an unforeseen accident, was energized, and the ground to a safe value for humans.
If the body of the electrical installation, which is energized, is not equipped with functional grounding, then a person’s touch 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.
When the functional grounding works properly, the current passing through a person will be safe. The tension during the touch will also be negligible. The bulk of the electricity will go through the grounding conductor to the ground.
Differences between working and protective grounding
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, then the second serves to protect people from electric shock. It also protects the equipment from damage in the event of a breakdown of some electrical device on the case. If the building is equipped with a lightning rod, this type of grounding will protectappliances from overload in the event of a lightning strike.
Working grounding of electrical installations, in case of an emergency, will play a protective role, but its main function is to ensure the correct uninterrupted operation of electrical equipment.
Functional grounding is used unchanged only at industrial facilities. In residential buildings, a grounding conductor is used, which is connected to the outlet. However, there are household appliances in the house that are fraught with a potential danger to the consumer, so it will not be superfluous to ground them using a solidly grounded neutral.
Home appliances that need to be connected to a working ground:
- Microwave.
- Oven and stove powered by electricity.
- Washing machine.
- PC system unit.
Ground design
Working grounding is iron pins driven into the ground, playing the role of conductors, to a depth of about 2-3 meters.
Such metal rods connect the ground terminals of electrical equipment to the ground bus, thereby forming a metal bond.
Metal bond is in every residential building. This is a welded iron structure that connects the upper ends of the ground electrodes to each other. She is brought to the introductory shield of the house for further wiring to 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. cable mainlyused to transfer functional ground from busbar to busbar.
For safety reasons, the electronic resistance of the metallic earth bond is periodically tested. It is measured from the ground terminal of the electrical installation to the ground ground loop furthest from it. The resistance value in any part of the working ground must not exceed 0.1 ohm.
Why do several grounding conductors
Electrical installation cannot be equipped with only one grounding conductor, since the soil is a non-linear conductor. The earth resistance is highly dependent on the voltage and the area of contact with the working earth pins plugged in. For one grounding conductor, the contact area with the soil will be insufficient to ensure the uninterrupted operation of the electrical installation. If you install 2 grounding conductors at a distance of several meters from each other, then a sufficient area of contact with the ground appears. However, it should be remembered that it is impossible to spread the metal parts of the ground too far, since the connection between them will be interrupted. As a result, there will be only two ground electrodes installed separately in the soil, not connected to each other in any way. The optimal distance between two ground loops is 1-2 meters.
How not to ground
According to paragraph 1.7.110 of the PUE, it is forbidden to use any type of pipeline as a working ground. In addition, it is forbidden to run the ground cableoutside and connect it to an unprepared pad on the bus. Such a ban is explained by the fact that each metal has its own individual potential. Under the influence of external factors, galvanic steam is formed, which contributes to the process of electroerosion. Corrosion can spread under the sheath of the ground wire, which increases the risk of melting when high currents are applied to the ground loop in the event of an accident. A special protective lubricant prevents the destruction of the metal, but it works only in a dry room.
Also, the PUE prohibits alternate grounding of electrical installations with each other, connecting more than one cable to one ground bus pad. If such 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. Corrective work is life-threatening if the working earth is connected incorrectly.
Requirements for grounding structures
To understand what is called working grounding, as well as what requirements apply to such structures, you should know that in order 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 built for grounding purposes meet all safety standards required to ensure the normal operation of networks and additional fuses from possible overload.
Dangercontact with live parts
When a person comes into contact with current-carrying parts of an electrical circuit or with metal structures that are energized as a result of a violation of the insulating layer of the cable, an 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, respiratory and cardiac arrest is possible. There are cases when an electric shock at low voltage leads to the death of a person.
Precautions against electric shock
To protect people as much as possible from contact with current-carrying parts of the electrical installation, as well as with its metal parts, it is necessary to completely isolate the dangerous object. To do this, install various fences around electrical installations.
