RCD is a tool that protects people from electric shock. In addition, it is designed to protect an apartment or house from a fire that can occur when the electrical wiring ignites. The RCD connection diagram without grounding must be correctly drawn up, otherwise it will only bring harm.
Factors affecting the correct connection of RCDs
- Understanding how it works. It depends on the connection method for certain working conditions.
- For a particular network, you should choose the right RCD.
- RCD disconnects the network in an emergency when the leakage current reaches a predetermined limit.
Connection of RCD and machine: circuit without grounding
For the home electrical network, certain protection devices and methods for connecting them are selected. The RCD connection scheme without grounding involves the installation of devices on separate lines or common to all wiring, after the main circuit breaker and meter. Preferably the devicelocated as close as possible to the source of electricity.
Usually, an RCD with a large rating (at least 100 mA) is installed at the input. It is mainly used as a fire extinguishing agent. After it, RCDs must be installed on separate lines with a cut-off current of not more than 30 mA. They provide human protection. When they are triggered, you can easily find out in which area the current leakage has occurred. The rest of the sections will operate as usual. Despite the costly connection method, all the positive factors are there.
For simple wiring with few ramifications, a 30mA RCD can be installed at the input for human protection and fire protection.
Protective devices are connected mainly in places that present the greatest danger. They are installed for the kitchen, where there are most electrical appliances, as well as for the bathroom and other rooms with high humidity.
Important! The RCD connection scheme without grounding requires the installation of a circuit breaker with each device, since the devices do not protect against short circuits and current increases above the norm. The switch is purchased separately, but you can buy a differential machine that combines the functions of both devices.
It is not allowed to connect wires to the wrong terminals of the device. If it fails, it may fail.
The connection diagram of a single-phase RCD without grounding allows the installation of a three-phase device instead, but in this case onlysingle phase.
How RCD works in the absence of grounding
When the insulation of the wires is damaged or the fasteners of the current-carrying contacts of the devices are loosened, current leakage occurs, leading to heating of the wiring or sparking, resulting in a fire hazard. If a person accidentally touches a bare phase wire, he can receive an electric shock, the passage of which through the body into the ground creates a danger to life.
The RCD connection diagram without grounding in an apartment or house provides for continuous current measurement at the inputs and outputs of protective devices. When the difference between them exceeds a predetermined limit, the electrical circuit is broken. Usually, grounding is done on the protected object. But it may not be.
In old Soviet-built houses, RCDs are used in circuits where there is no protective conductor PE (grounding). From the main three-phase house network, a phase wire and a neutral wire are connected to the apartment wiring, which is combined with a protective conductor and is designated PEN. In a three-phase apartment network, there are 3 phases and a PEN conductor.
A system with combining the functions of working N and protective PE conductors is called TN-C. From the city overhead line, a cable with 4 wires (3 phases and neutral) is introduced into the house. Each apartment receives single-phase power from the interfloor shield. The neutral wire combines the functions of a protective and working conductor.
Schemeconnecting an RCD in a single-phase network without grounding is different in that if a phase breaks down and hits the case, the protection will not work. Due to the lack of grounding, no cut-off current will flow, but a life-threatening potential will appear on the device.
When touching the electrically conductive parts of the body of an electrical appliance, an electrical circuit is created to pass the current through the body. If the leakage current is below the threshold value, the device will not work, the current will be safe for life. If the limit is exceeded, the RCD will quickly disconnect the line from touching the case. If there is a ground on it, the circuit can be disconnected before a person touches the case, as soon as the insulation breakdown occurs.
Features of connecting differential protection in three-phase networks
In accordance with the PUE, the installation of RCDs in three-phase networks of the TN-C system is prohibited. If the electrical receiver needs to be protected, the grounding PE conductor should be connected to the PEN conductor before the RCD. Then the TN-C system is transformed into the TN-C-S system.
In any case, the RCD must be connected to increase electrical safety, but this must be done according to the rules.
RCD selection
The differential machine is selected with a power one step higher than that of the circuit breaker connected to it in the same line. The latter is designed to work with an overload for a few seconds or minutes. An RCD of the same power as it is not designed for such loads and may fail. Low-power devices are used at a current of not more than 10 A, and powerful devices are used above 40 A.
When voltage is in220 V apartment, a two-pole device is selected, if 380 V is a four-pole device.
An important characteristic of the RCD is the leakage current. It depends on its value whether to use the device as a fire-fighting or for protection against electric shock.
Devices have different response speeds. If you need a high-speed apparatus, a selective one is selected. There are 2 classes here - S and G, where the latter has the highest speed.
The structure of the machine can be electromechanical or electronic. The first does not require additional power.
By marking, you can distinguish the type of leakage current: AC - variable, A - any.
Errors in the installation and operation of the RCD
- It is not allowed to connect the output neutral wire of the RCD to an open area of the electrical installation or switchboard.
- The neutral and phase wires must be connected through a protective device. If the neutral bypasses the RCD, it will work, but false trips may occur.
- If you connect zero and ground to the same terminal in the outlet, the RCD will constantly trip when the load is connected.
- It is not allowed to install a jumper between the neutral wires of several consumer groups if separate protective devices are connected to them.
- Phases are connected to the terminals marked "L", and zero - to "N".
- It is not allowed to turn on the device immediately after operation. First you need to find and fix the problem, and then connect.
Connecting an RCD without grounding in an apartment
Insulation breakdown in the absence of grounding leads to the appearance of a potential on the instrument case, which is dangerous to humans. Leakage here will occur only after touching. In this case, the entire leakage current will pass through the body until it reaches the threshold value and the protective device disconnects the circuit.
Connecting an RCD to sockets
In the presence of a TN-C system, the device case is sometimes connected to the neutral wire. The connection diagram of an RCD without grounding for sockets provides for connecting the neutral to the side terminal 3. Then, if the wire breaks down, the current from the device case will go through it. The connection must be made at the entrance to the apartment.
This is against the rules as it increases the chance of electric shock. If voltage hits the neutral in the external network, it will be on the cases of electrical appliances grounded in this way. Another disadvantage of this method is the frequent operation of the circuit breaker when loads are connected.
This connection cannot be made by yourself. If everything is done according to the standard, it is necessary to order a project for changing the power supply system in accordance with the requirements of the PUE. Basically it should be changing the system to TN-C-S as follows:
- transition inside the apartment from a two-wire to a three-wire network;
- transition from intra-house four-wire network to five-wire;
- separation of the PEN conductor in an electrical installation.
Features of wiring for connecting RCD
When an RCD is connected in a single-phase network without grounding, the wiring is done with a three-wire cable, but the third conductor is not connected to the zero terminals of the sockets and instrument cases until the system is upgraded to TN-C-S or TN-S. With the PE wire connected, all conductive cases of the devices will be energized if the phase falls on one of them, and there is no grounding. In addition, the capacitive and static currents of electrical appliances are summed up, creating a risk of injury to a person.
Without experience in wiring and electrical equipment, the easiest way is to purchase an adapter with an RCD for 30 mA and use it when connecting to electrical outlets. This connection method greatly improves electrical safety.
For electrical appliances and sockets in the bathroom and other areas with high humidity, it is necessary to install an RCD for 10 mA.
Scheme for connecting an RCD in a single-phase network without grounding in a private house
Home network can be the same as in the apartment, but here the owner has more options.
The easiest way is to install one common or several RCDs at the input on the main lines of the home network. For a complex network, several layers of protective devices are connected.
Introductory RCD 300 mA protects all wiring from fire. In addition, it can operate on the total leakage current from all lines, even if they have leakage inwithin normal limits.
Universal RCDs for operation at 30 mA are installed after the fire, and the next lines should be the bathroom and children's room with Iy=10 mA.
How to connect grounding in a private house
You can make a ground loop and convert the network to TN-C-S. It is not recommended to independently connect the re-grounding to the neutral wire. When voltage hits the neutral from the external network, this grounding may become the only one for all neighboring houses. If not properly executed, it can burn out and cause a fire. It is advisable to re-ground at the outlet from the overhead line, which minimizes the likelihood of a fire in the house.
Connecting an RCD in the country
In the country, the wiring diagram is simple, and the loads are small. Here, the RCD connection diagram in a single-phase network is suitable (photo below). RCD is selected for 30 mA (universal), with protection against fire and against electric shock.
The connection diagram for an RCD without grounding in the country requires the installation of a main input and a pair of machines for lighting and sockets. If a boiler is used, it can be connected via a socket or a separate machine.
Conclusion
The RCD connection diagram without grounding is a common method of protection. The ground also serves as a protection and must be connected correctly. It is important to pay attention to the additional protection of the bathroom and other rooms with high humidity. RCD is expensive, butelectrical safety is more important here. In complex wiring diagrams, it is advisable to install several stages of protection with selective operation of an RCD of a smaller rating.
It is important to understand that an RCD is the only type of device designed to protect a person from electric current.
