How to connect a residual current device in an apartment without grounding: parsing schemes and step by step instructions

Construction standards, tied to modern conditions, are designed to take into account a significant amount of electrical equipment, which is traditionally equipped with housing. The obvious point in this case seems to be the protection of homeowners from possible electric shock. As a rule, one of the main protective devices is the RCD.

It is thanks to this device that a sufficiently effective protective barrier is organized. However, when addressing it, questions always remain relevant, for example, how to connect an RCD in an apartment without grounding.

The need for grounding the RCD

It is believed that the flawless functioning of the safety device is achieved only if there is an electrical network with a phase contact conductor, a “zero” conductor and a grounding bus.

In fact, if we consider the operation of the RCD and the grounding bus, both devices are functionally designed to perform similar actions - to de-energize the circuit in case of leakage of electricity to the case. The difference is noted only in the circuit principle.

Bundle Automat-UZO
A classic assembly pair, thanks to which a completely effective blocking is provided both from electric shock and possible fires due to short-circuit fault: 1 - automatic; 2 - protection device (RCD)

From this follows a logical conclusion: both circuit solutions are applicable in the practice of power supply to the home. Moreover, the best option is to share these two circuit solutions.

If the power supply line is installed RCD, the organization of grounding, by and large, it is permissible to exclude. At the same time, the introduction of a protective device seems to be a reasonable solution for a two-wire power grid where there is no technical grounding bus.

RCD in conjunction with grounding
The optimal technical solution for the construction of electrical circuit wiring of residential buildings, when along with the protective device disconnect also involved grounding bus. Such solutions are the standard for new buildings.

Actually, if you carefully examine the device of the RCD, it will not be able to find terminals specifically designed to connect the "earth".

This factor confirms once again the possibility of switching on without grounding. However, modern housing construction projects necessarily require the presence of a grounding bus.

How does the protective device without the "land"

The connection option without grounding is a typical case for apartments and private houses of old buildings. The power supply of such buildings, as a rule, is organized without the supply of grounding bus. But how correct is the action of the RCD without the inclusion of "earth"?

Connection of RCD without grounding
Wiring option, widespread in relation to the real estate projects of the old sample. The introduction of protective disconnect devices into the old infrastructure has to be carried out in the absence of an earth bus.

For example, during the operation of electrical equipment there was a breakdown on the case. Under conditions of absence of a grounding bus, it is not necessary to count on instantaneous tripping of the RCD.

If a person touches the body of the pierced equipment, the leakage current will flow to the “ground” through the human body.It will take some period of time (device setting threshold) until the moment when the RCD operates.

During this period of time (rather short), the risk of injury from the effects of electric current remains completely acceptable. Meanwhile, the RCD would have triggered immediately if there was a ground bus.

Leakage current without ground
The electrical wiring scheme without the presence of "earth", where the protective device is connected without an additional earth bus, still remains to some extent dangerous for the user. In such situations, the RCD should be carefully adjusted to the threshold.

In this example, it is easy to draw a conclusion on the fact that connecting a UZO in the apartment panel or panel of a private house should always be accompanied by connection to the ground bus. Another question is that a sufficient number of buildings remain, where it is not possible to do this due to the lack of “land” in the project schemes.

For variants of buildings where the power supply is organized without grounding, the switching protection device by means of UZO actually looks like the only effective means of protection that can be applied in such conditions.Therefore, we consider the possible schemes applicable to the supply of private housing.

Connection diagrams for RCD without grounding

One of the traditional circuit solutions where a protective device UZO is used is the option of installing the device directly at the input of power supply to the structure of the object. That is, the protective shutdown device is mounted immediately after the electricity meter.

WCD layout
Traditional connection, typical for the majority of cases of use of the protection device on the electric power lines in the private sector: 1 - electric meter; 2 - RCD; 3 - terminal block bus linear "zero"; 4 - automatic load

This approach ensures the protection of the electrical wiring of the dwelling in full, which means that current leakage of any household electrical appliance is monitored. From the electrical network, voltage is supplied by cable to the device, which combines two phase and two zero terminals in one case (there are also three-phase devices).

These two pairs of terminals are divided into input and output. Through one pair passes the phase line, through the other zero. After completing the layout according to this scheme, then install additional machines for each type of load.

RCD for three-phase connection
Execution of a three-phase device: 1 - terminal for supplying a zero bus; 2 - the value of the operating current; 3 - the value of permissible overcurrents; 4 - cut-off current value; 5 - type of instrument; 6 - phase terminals; 7 - test key; 8 - action indicator; 9 - cocking key

The advantage of this circuit is the savings on electrical equipment. Just installing one device successfully solves the issue of protection. However, on the other hand, if an object of current leakage appears in the home network, the house is completely de-energized.

For some cases, this situation may not be appropriate. To some extent, reduced comfort component for property owners. It is possible to resolve this drawback with the help of another circuit design - more functional in terms of sectional switching off.

Extended functionality circuit breaker circuit

A slightly different circuit design, involving the introduction of an RCD on each separate branch of the power supply, allows you to make the protection more “soft” in relation to the power interlock.

Functionally extended circuit
A somewhat modified version of the circuit solution, where two (or several) protective devices are used. In this case, one acts as an input, the rest as intermediate: 1, 2 - strips of terminals of the zero bus

Here, several protection devices are used, depending on the number of branches of the electric apartment network. For example, if there are two branches, the scheme will look like the following:

  1. Installation of a single RCD as in the first version - at the input.
  2. Installation of the following RCDs after the automata of the network taps
  3. On each branch line protection by the number of consumers.

With this construction of the control circuit and the cut-off voltage is carried out in relation to a separate branch of household electrical wiring.

Therefore, the fact of current leakage, fixed on a separate line, will result in blocking only the network section on which the punched load is connected. The remaining sites will remain in working condition.

Extended RCD version
For the case of circuit layout shown above, an increase in the overall dimensions of the control cabinets is characteristic. Therefore, this option is not always acceptable for the device in the conditions of private houses.

But with a more functional solution does not do without certain drawbacks. It is clear that with the increase in the number of devices will have to expand the switchboard.Increasing the size of the switchboard can also be a problem for the user. Moreover, from the financial side, the choice of applying the noted scheme is also not entirely successful.

Costs will be almost double the increase compared with the first option. True, if you already think about effective full-featured protection, it is not recommended to save money.

Private households and connection details

Private buildings differ from apartments of municipal housing significantly. Primarily the use of equipment that is never used in apartments. For example, the traditional equipment of a private household are electric heating systems or an electric heating module for a bath.

Wiring diagram of the boiler through the RCD
Often it is required to turn on the protective blocking device in the power supply circuits of powerful household appliances. As in this case, when an electric boiler is involved in the private residential sector. For such equipment, the earth tire is mandatory

For any of these systems, it is imperative to install a protective disconnection, since it is not just household appliances, but rather powerful technological equipment.Here, the RCD is not only a protection against current leakage into the case, but also serves as a fire protection device.

With respect to such projects, a schematic solution based on the TT system is often used, providing relative safety in cases of leakage of currents on the equipment case.

TT Connection Diagram
The "TT" scheme for electrical networks where a deafly grounded neutral is used: 1 - a transformer with a grounded neutral bus; 2 - limiting resistor; 3 - residual current device; 4, 5 - sections of consumer load

The addition of such a scheme with a protective interlock device contributes to an increase in the degree of reliability. However, the TT system requires a ground bus.

Step-by-step instructions for the implementation of protection

For complete information on the connection of devices providing a protective cut-off, consider step by step the process of creating a communication circuit with the introduction of a protection device.

  1. To bring to the shield the power cable from the centralized interface of energy input to the house.
  2. Mount a circuit breaker inside the shield (this device is previously calculated for cut-off according to the total network load).
  3. Mount the electric meter in a convenient place and connect the output of the machine with the input terminals of the meter.
  4. Install inside the RCD panel and connect the instrument input (upper terminals) to the output terminals of the meter.
  5. On the output (phase) terminal of the UZO connect the phase conductor of the household wiring.
  6. On the output (zero) terminal of the RCD, connect the neutral conductor of the household wiring.
  7. Connect the main cable at the terminals of the input circuit breaker.

Performing marked operations, you should consider some of the nuances. For example, it is necessary to follow the rule of sequential switching on of an automatic switch with a protective cut-off device.

If, however, it is not planned to introduce an automatic circuit into the network, it is necessary to install fuses instead of the automatic one.

220 Fuses for Networks
Fuse-links that can be used to protect electrical circuits by short-circuit currents. Fusible elements can sometimes be used to protect, replacing the functions of circuit breakers

As a rule, the value of the rated current of the protection module is recommended to take a little more than the value of the current of the circuit breaker. In some cases, this parameter is allowed to be chosen equal to the parameters of the machine.

When performing work on the inclusion of a protective device in the power supply network, it is recommended to check all available circuits for possible defects.

After installing the instrument, be sure to check the effectiveness of the cutoff. For this operation there is a special test key on the front panel of the device.

RCD test key
Keys test the correct operation of protection. After installing and connecting the RCD, use these elements of the device to test the protective function.

When installing, all jointing work must be carried out carefully.

The supply of power lines should be made in exact accordance with the symbols on the device body. That is, the phase is connected to the “phase” and, accordingly, the zero is connected to the “zero”. There is a high risk of failure of the protective apparatus from changing places of the “components”.

Conclusions and useful video on the topic

This video concludes the article on devices used as protective systems for electrical networks, equipment and users of apartments and private houses. Survey material with all the subtleties of use,which will certainly come in handy for practice.

Connecting an RCD without earthing in modern-type apartments is not only not recommended, but also prohibited. If you need to install equipment in the switchboard, be sure to contact the master serving the house. All work concerning the filling of the apartment building must be performed by a qualified specialist.

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