Working and protective grounding: description, principle of operation and purpose, connection diagrams and differences,

During the operation of electrical appliances, grounding devices must be used. In accordance with the purpose, it is possible to use protective and working grounding. The first type allows you to ensure the normal operation of the equipment, and the second is designed to protect people. These types of security measures have different purposes and principles of operation.

Protection of electrical equipment

Working (functional) grounding - connection to the ground of certain points of current-carrying parts of electrical equipment. Most often it is neutral points of windings of transformers and generators. To implement this type of protection, reliable conductors or special devices, for example, breakdown fuses, are used. The main task of working grounding is to prevent short circuits and failures in the operation of electrical installations.

According to safety regulations, these types of protection against electric shock cannot be combined. The fact is that interference currents (for example, atmospheric discharges) can be superimposed on those flowing in an electrical circuit. As a result, the equipment may be damaged and the protective earth will not function properly. It should also be remembered that the functional resistance indicator should not exceed 4 ohms.

Protective earth

Due to the electrical connection of metal structures of industrial and domestic equipment to the ground increases the safety of its operation. This method of protecting people from electric shock is called protective grounding. Even if special automatic devices are used in the circuit, the speed of their operation does not allow a person to be completely safe.

Principle of operation

If the phase conductor touches the metal structure of the equipment, then its case will be energized. If this type of protection has been organized correctly, then an electrical circuit with low resistance is created. As a result, this path will become more preferable for the current, the touch of a person to the body will be safe. This is how you can briefly describe the principle of protective grounding.

Main functions:

1. Protection is provided even in a situation where hazardous voltages on the case were generated by inductive currents and not by short circuits.
2. The use of a dead-grounded neutral makes it possible to obtain, in case of a short circuit, long-term pulses with a large amplitude, which contribute to the operation of the protective automatics.
3. The grounding conductor is capable of providing reliable protection of the equipment in the event of a lightning strike.

The latter function is not intended and is of secondary importance. The main purpose of protective grounding is to ensure the safety of people while working on the equipment.

Connection diagrams

To select the optimal protection option, you should understand the grounding schemes, as well as their advantages and disadvantages. The first type is a deafly grounded neutral (type TN). This circuit is used in household and industrial electrical equipment designed to operate in networks up to 1 kV. For its implementation, the neutral wire of the power source is connected to the ground electrode. Then the housing, shield and chassis are connected to the common conductor.

The most popular are three schemes, indicated by the corresponding letter:

1. C - the conductor performs both protective and working functions. The circuit is extremely simple to implement, but when the electrical circuit is broken, it loses its protective properties.
2. S - two separate neutral wires are used. The cost of the circuit is somewhat higher, but its reliability increases significantly.
3. C-S is a combination of the two previous systems. When using it, it is necessary to take measures to prevent mechanical damage to the protective conductors, otherwise the circuit will cease to perform its function.

The TT scheme is used on overhead power lines. A solid-grounded neutral is connected to the power source, and energy is transmitted through four conductors. On the consumer's side, an autonomous protection system is mounted, to which the equipment is connected.

Another scheme for implementing this type of protection is the IT scheme. It is actively used in research centers, as it allows you to additionally eliminate spurious electrical interference. To reduce the resistance index, it is necessary to shorten the length of the conductor. This problem is solved by creating a special grounding loop around the perimeter of the object.

Categories of grounding conductors:

1. Artificial - made specifically to create protective grounding and should not be covered with paints and varnishes. It is allowed to use electrically conductive concrete as a ground electrode.
2. Natural - electrically conductive parts of networks and communications of buildings that are in contact with the ground.

This classification is conditional, since in any case, metal parts of the building located in the ground are used to ensure the safety of people. It is recommended to create protective grounding using natural grounding conductors. However, to solve this problem, it is forbidden to use pipelines that supply flammable substances.

The purpose and device of protective grounding differs significantly from the functional one, therefore they cannot be combined. In detail, the issues of organizing the protection of equipment and people from the effects of electric current are set out in a special document "Rules for the Installation of Electrical Installations".