The main requirement for any electrical appliance is operational safety. This is especially true for equipment in contact with water. In the absence of additional protection, even a small problem with the electrical wiring (burn-through of the insulating layer, puncture between the turns of the engine) is dangerous. An electrical potential appears on the body of the faulty device. In this case, a person or an animal touching the body may get an electric shock. To avoid this, protection methods such as neutralization and grounding have been developed.

Grounding tasks

An artificially created contact between an electrical installation and the ground is called grounding. Its task is to lower the voltage on the device case to a level that is safe for living beings. In this case, most of the current is diverted into the ground. In order for the grounding system to work effectively, its resistance must be significantly lower than in the rest of the circuit. This requirement is based on the property of the electric current to always choose the smallest resistance on its way.

Note! Grounding is used exclusively on power grids with isolated neutral.

The fault current is sometimes insufficient when using an earthing switch with a resistance that is relatively high for the reaction of protective devices. Therefore, another task of the grounding system is the growth of the emergency fault current.

Types of grounding devices:

1. Lightning protection. They divert impulse currents entering the system as a result of lightning strikes. They are used in lightning rods and arresters.
2. Workers. Designed to maintain the normal performance of electrical installations. They are used in both normal and emergency situations.
3. Protective. Protect people and animals from electric shock passing through metal objects in case of breakdown of phase conductors.

Grounding devices are natural and artificial:

1. Metal products are considered natural, the main function of which is not to drain current into the ground. These ground electrodes include pipelines, reinforced concrete elements of buildings, casing lines, etc.
2. Artificial earthing devices are systems designed specifically for current drainage. These are steel strips, pipes, corners and other metal elements.

For the grounding system, pipes intended for transporting flammable substances (both gases and liquids), aluminum parts, cable sheaths must not be used. Also, objects covered with an anti-corrosion insulating layer are not suitable for this purpose. It is forbidden to use water and heating pipes as grounding conductors.

Technical design of grounding systems

There are several connection schemes with a different composition of protective and working conductors:

• TN-C;
• TN-C-S;

The type of grounding is indicated by the first letter in the designation:

• I - live elements do not touch the ground;
• T - the neutral of the power supply is grounded.

The grounding method for exposed conductors is determined by the second letter:

• N - direct contact between the grounding point and the power source;
• T - direct connection with the ground.

After the hyphen, there are letters indicating the method of functioning of the protective PE and working N neutral conductors:

S - the work of conductors is provided by a single PEN conductor;

C - there are several conductors.

TN system

The TN-type grounding includes subsystems TN-C, TN-S, TN-C-S. The oldest of these subsystems, TN-C, is used in 3-phase four-wire and 1-phase two-wire power grids. Such networks are usually found in old buildings. For all its simplicity and relatively low cost, the system does not provide a sufficient level of security, and therefore is not used in new buildings.

Subsystem TN-C-S is used for renovation of old buildings. It is relevant where the working and protective conductors are combined at the input. The use of TN-C-S is necessary for the reconstruction of the system when computer or telecommunication equipment is installed in the old building. This ground is a transitional type between TN-C and the most modern subsystem - TN-S. TN-C-S is a relatively safe and affordable financial grounding scheme.

The difference between the TN-S subsystem from other types of such equipment is the location of the working and neutral conductors. They are installed separately, with the neutral PE conductor uniting all existing conductive elements of the electrical installation. To avoid duplication, create a transformer substation equipped with a main grounding. An additional advantage of the substation is the ability to reduce the length of the conductor running from the cable entry into the equipment to the ground electrode.

TT system

In this grounding system, current-carrying open elements are in direct contact with the ground. In this case, the electrodes do not depend on the substation neutral grounding device. TT is used when, for technical reasons, it is impossible to build a TN system.

IT system

In this system, the neutral of the power supply does not touch ground or is grounded by a high impedance installation. The circuit is popular in situations where it is necessary to connect sensitive equipment (hospitals, laboratories, etc.).

Zeroing

The neutralization process consists in combining non-energized metal elements with the grounded neutral of a 3-phase step-down current source. Also use the grounded terminal of the 1-phase current generator. Zeroing is used to provoke a short circuit in the event of a breakdown of the insulating layer or penetration of current into a non-current-carrying equipment element. The meaning of the short circuit is that after that the circuit breaker is triggered, the fuses are blown out, or other protective means are turned on. Zeroing is used in electrical installations with solidly grounded neutral.

If you install a residual current device on the line, it will trip due to the difference in current strengths on the phase and zero. The circuit breaker installed in addition to the RCD will allow both devices to operate in the event of a breakdown, or to connect the fastest connecting protection element.

When installing grounding, it should be borne in mind that a short circuit should lead to melting of the fuse or disconnection of the circuit breaker. If this does not happen, the free flow of the fault current in the electrical circuit will cause a voltage to appear on all zeroed objects, and not only at the breakdown site. The voltage indicator is the product of the zero resistance and the fault current, which is very dangerous when a living creature is struck by current.

It is necessary to carefully monitor the good condition of the neutral conductor. When it is broken, a voltage arises on all zeroed elements, since they automatically come into contact with the phase. For this reason, it is forbidden to install any protective devices on the neutral conductor (in addition to switches and fuses), due to which a break occurs when triggered.

To reduce the risk of electric shock when the neutral conductor is broken, additional grounding is created every 200 meters of the line, as well as on the end and input supports. The resistance level on each new earthing switch should not be higher than 30 ohms.

Difference between grounding and zero

The main difference between grounding and earthing is the purpose of the systems. Grounding is necessary to quickly reduce the voltage to an acceptable level. The task of grounding is to completely turn off the current in the area where a breakdown to the case or other non-conductive element has occurred. Zeroing is associated with a decrease in the potential of the housing in the period between closing and disconnecting the electricity supply.

In new buildings, grounding is not used. In new buildings, a 3-wire cable with a phase, neutral and earth (1-phase system) or a 5-wire cable (three phases, neutral and earth) is installed in a 3-phase system. The most commonly used scheme is TN-S, but TN-C-S is also found.

Do I need to do grounding in the apartment

It is not worth using zeroing in order to protect residents and electrical installations in an apartment - there are situations when a refrigerator (or other device) is zeroed, and a current breakdown occurs. Also, incorrectly performed electrical wiring is often found (after all, an electrician could have confused the wires and connected a phase instead of zero). In such cases, household appliances fail even before the circuit breaker is triggered.

Installation of a residual current device, differential circuit breaker or circuit breaker is necessary only together with grounding.

Grounding and grounding requirements

All electrical installations and circuits equipped with neutral conductor insulation require installation of a protective system (neutralization or grounding).

There are several rules to follow when creating a security system:

1. Zeroing must be done for installations with a solidly grounded conductor with a power of up to 1000 volts. Grounding in such systems is not done.
2. Zeroing should be supplied with a 380 volt transformer. In a zeroed system, the secondary voltage should not exceed 380 volts, and the step-down voltage should not exceed 42 volts.
3. When grounding, it is allowed to connect from the separating transformer to only one consumer of electricity. The current rating of the protective device is up to 15 amperes. Neutralization or grounding of the secondary winding is not allowed.
4. When grounding zero in a 3-phase electrical circuit, it is necessary to put protection against current breakdown. Mount it in the neutral conductor or phase from the lower voltage.
5. Protective grounding or neutral grounding must be created at installations located on the street, as well as in especially dangerous working conditions. The voltage rating is 42 volts (alternating current) or 110 volts (direct current).
6. For voltages above 380 volts (direct current) and 440 volts (alternating current), protection is required regardless of other conditions.

Subject to grounding:

• housings of electrical installations;
• equipment drives;
• frame parts and metal structures of electrical cabinets and panels;
• secondary transformer windings;
• steel cable sheaths;
• busbars;
• cables;
• metal pipes for wiring;
• electrical equipment mounted on moving elements.

As for housing, grounding and grounding is necessary for electrical household appliances with a capacity of more than 1300 watts. Metal products such as bathtubs and shower trays, suspended ceilings are subject to grounding for potential equalization.

A dedicated conductor is used to ground air conditioners, electric stoves or similar electrical consumers with a capacity of more than 1,300 watts. It should be connected to the zero of the mains.

Note! The cross-sections of the phase and neutral conductors must be the same.

A detailed list of electrical installations requiring protection by grounding or grounding is indicated in the Electrical Installation Rules. PUE is an official document, it contains all the standards. The document also establishes a list of equipment for which protection is optional.

The creation of a grounding and grounding system is extremely important, the safety of people and the preservation of property depend on it. Therefore, the cost of a mistake is high. It is recommended that only qualified workers be assigned this work.