RCD is a tool that protects people from electric shock. In addition, it is intended to protect the apartment or house from fire, which can occur when the electrical wiring is ignited. The RCD connection diagram without grounding must be properly designed, otherwise it will only bring harm.
Factors affecting the proper connection of an RCD
- Understanding the principle of work. The connection method for certain operating conditions depends on this.
- For a specific network, the RCD should be selected correctly.
- The RCD disconnects the network in an emergency when the leakage current reaches a predetermined limit value.
RCD and machine connection: circuit without grounding
For the home electrical network, certain protection devices and methods for connecting them are selected. The RCD connection diagram without grounding involves the installation of devices on separate lines or common to the entire wiring, after the main circuit breaker and counter. Preferably, when the device is located as close as possible to the source of electricity.
Typically, an RCD with a large rating (at least 100 mA) is installed at the input. It is used primarily as a fire fighting agent. After it, RCDs should be installed on separate lines with a cut-off current of not more than 30 mA. They provide human protection. When they are triggered, it is easy to detect in which area a current leak has occurred. The remaining sections will work as usual. Despite the costly way to connect, all the positive factors are there.
For simple wiring with a small number of branches, it is possible to install a 30 mA RCD at the input, which performs the functions of human protection and as a fire protection.
Protective devices are connected mainly in areas of greatest danger. They are installed for the kitchen, where the most electrical appliances, as well as for the bathroom and other rooms with high humidity.
Important! The RCD connection diagram without grounding requires the installation of a circuit breaker together with each device, since the devices do not protect against short circuit and current increase above normal. 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 only one phase is used.
How RCD works in the absence of grounding
When the insulation of the wires is damaged or the fastenings of the current-carrying contacts of the devices are weakened, current leakage occurs, leading to heating of the wiring or sparking, resulting in a risk of fire. If a person accidentally touches a bare phase wire, he may receive an electric shock, the passage of which through the body into the earth creates a danger to life.
The RCD connection diagram without grounding in an apartment or in a house provides for continuous measurement of the current at the inputs and outputs of protective devices. When the difference between them exceeds a predetermined limit, an 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 is connected to the apartment wiring, which is combined with a protective conductor and is indicated by PEN. In a three-phase apartment network there are 3 phases and a PEN conductor.
The system, combining the functions of the working N and protective PE conductors, is called TN-C. A cable with 4 wires (3 phases and neutral) is introduced into the house from the city overhead line. Each apartment receives single-phase power from the floor board. The neutral wire combines the functions of a protective and working conductor.
The connection circuit of the RCD in a single-phase network without grounding is different in that if the breakdown and phase gets into the housing, the protection will not work. Due to the lack of grounding, the cut-off current will not flow, but life-threatening potential will appear on the device.
When you touch the electrically conductive parts of the body of the appliance for the passage of current creates an electrical circuit into the ground 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 housing. If there is grounding on it, the circuit can be disconnected before a person touches the case, as soon as an insulation breakdown occurs.
Features of connecting differential protection in three-phase networks
In accordance with the EMP, 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 converted to the TN-CS system.
In any case, the RCD must be connected to increase electrical safety, but this must be done according to the rules.
RCD selection
A differential circuit breaker is selected with a power one step higher than that of a circuit breaker connected to it in one line . The latter is designed to work with overload for several seconds or minutes. The RCD of the same power with it is not designed for such loads and can fail. Low-power devices are used at a current of not more than 10 A, and powerful devices are higher than 40 A.
With a voltage in the apartment of 220 V, a two-pole device is selected, if 380 V is a four-pole device.
An important characteristic of an RCD is the leakage current. It depends on its size to use the device as a fire fighting device or to protect against electric shock.
Devices have different response speeds. If you need a high-speed device, select selective. There are 2 classes - S and G, where the latter has the highest speed.
The structure of the machine may be electromechanical or electronic. The first does not require additional food.
By marking, you can distinguish the type of leakage current: AC - alternating, A - any.
Errors during installation and operation of RCD
- It is not allowed to connect the output neutral wire of the RCD to an open section of the electrical installation or switchboard.
- The neutral and phase wires must be connected through a protective device. If the neutral passes the RCD, it will work, but false positives may occur.
- If you connect zero and ground to the same terminal in the outlet, the RCD will constantly operate 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 make the connection.
RCD connection without grounding in the apartment
A breakdown of insulation in the absence of grounding leads to the appearance on the device body of a potential that is dangerous to humans. A leak here will occur only after touching. In this case, the entire leakage current will pass through the body until it reaches a threshold value and the protective device disconnects the circuit.
Connecting RCDs to outlets
With the TN-C system, the instrument case is sometimes connected to a neutral wire. The RCD connection diagram without grounding for outlets provides for the connection of a neutral to the side terminal 3. Then, when a wire is broken, the current from the device will go through it. Connection should be done at the entrance to the apartment.
This is a violation of the rules, as the likelihood of electric shock increases. If voltage gets to neutral in an external network, it will be on the cases of similarly grounded electrical appliances. Another disadvantage of this method is the frequent operation of the circuit breaker when connecting loads.
This connection cannot be done 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 EMP. In essence, this should be a change to TN-CS as follows:
- transition inside the apartment from a two-wire to a three-wire network;
- transition from an intra-house four-wire network to a five-wire;
- separation of the PEN conductor in an electrical installation.
Features of electrical wiring for connecting an 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 outlets and the instrument cases until the system is upgraded to TN-CS or TN-S. When the PE wire is connected, all the conductive housings of the devices will be energized if the phase falls on one of them and there is no grounding. In addition, capacitive and static currents of electrical appliances are summed up, creating the danger of human injury.
Having no experience in installing wiring and electrical equipment, it is easiest to purchase an adapter with a 30 mA RCD and use it when connected to electrical appliances sockets. This connection method significantly increases electrical safety.
For electrical appliances and sockets in the bathroom and other rooms with high humidity, it is necessary to install an RCD of 10 mA.
RCD connection diagram in a single-phase network without grounding in a private house
The home network may be the same as in the apartment, but here the owner has more options.
The easiest way is to install at the entrance one common or several RCDs on the main lines of the home network. For a complex network, several levels of protective devices are connected.
An introductory RCD of 300 mA protects all wiring from fire. In addition, it can be triggered by the total leakage current from all lines, even if they leak in the normal range.
Universal RCDs for tripping at 30 mA are installed after the fire, and the next lines should be a bathroom and a children's room with I y = 10 mA.
How to connect grounding in a private house
You can make a ground loop and convert the network to TN-CS. It is not recommended that you reconnect the neutral ground wire to yourself. If voltage gets to the neutral from an external network, this grounding may become the only one for all neighboring houses. With poor performance, 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.
RCD connection 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). The RCD is selected at 30 mA (universal), with protection against fire and electric shock.
The RCD connection diagram without grounding in the country requires the installation of the main input and a pair of machines for lighting and sockets. If a boiler is used, it can be connected via an outlet or a separate machine.
Conclusion
The RCD connection diagram without grounding is a common method of protection. Grounding also has a protective function and must be connected correctly. It is important to pay attention to the additional protection of the bathroom and other rooms with high humidity. RCDs are expensive, but electrical safety is more important here. In complex wiring diagrams, it is advisable to install several protection levels with selective operation of a lower rated RCD.
It is important to understand that RCDs are the only type of apparatus designed to protect a person from electric current.