Residual current device or residual current circuit breaker is an electromechanical device, carrying out automatic shutdown of electricity in the network when reaching differential current a certain value. In circuits with a voltage of 380 V, a 3-phase RCD is installed. This device differs in the presence of 3 or 4 poles for connecting to an electrical network.
Content
- Purpose of the device
- Device and principle of operation
- Types of protective devices
- Popular models
- Electrical connection
Purpose of the device
A three-phase RCD protects electronic and electrical devices from short circuits within the network, protects the circuit from fires due to current leakage. But the main task of this device is protection of people from electric shock.
This can happen if a person accidentally touches bare wires or the housing of a household appliance with a broken insulation. If such a situation arises, the three-phase RCD will automatically disconnect the electricity from the network.
It is worth noting that single-phase 3 RCDs for 3 phases cannot be installed, since only one device will work, and the rest will be connected to the network. The principle of operation is the same for all devices. When switched on, the device compares the values of the current passing through it.
Often, protective equipment is installed in a network with an electric motor, in which the stator windings are delta-connected. In the event of a breakdown of the winding onto the case, the protective device will instantly de-energize the electrical circuit. Sometimes three-phase devices are mounted in a 220 V network if a welding unit is connected to it.
Device and principle of operation
The device is based on a differential transformer. It is a magnetic circuit made of a ferromagnetic material, on which the windings are wound.
In the normal state, the currents flowing create electromagnetic fluxes moving in different directions, but the same in value. Therefore, the total magnetic flux will be zero and the protective device will not work.
As soon as a person touches the body of an electrical appliance with damaged insulation, a leakage current immediately begins to flow through the RCD. Due to the fact that the values of the currents will be different, the resulting value of the magnetic flux will not be zero.
An electromotive force will appear in the test winding, which will generate an electric current. Under its influence, the magnetoelectric relay will work and disconnect the power contacts. The protective device reacts to a small leakage current, the threshold value of which does not exceed 10 mA.
This is the difference between these devices and machines that respond to overloads and short circuits. The RCD will not turn off even if a person touches the phase and neutral wires, since it will act as a load that allows electricity to pass through.
Types of protective devices
The main types of protective devices are subdivided into electronic and electromechanical. On the basis of these parameters, consumers choose the necessary devices. In addition, the technical characteristics of the devices are taken into account, the main of which is the value of the rated current. This parameter is determined from the ratio of the maximum load to the voltage value. The devices are divided according to the leakage current, it starts from 10 mA and can reach 300 mA. Protective devices include:
- AC - devices are disconnected when there is an AC leakage;
- A - universal devices that are suitable for all cases;
- B - used in production facilities.
Electromechanical devices operate independently of the voltage of the electrical network, while the operation of electronic devices, on the contrary, is influenced by the mains voltage. If a grounding system is installed in the network of a private house, then the use of a three-phase RCD is all the more necessary. Protective devices are divided:
- on adjustable (discrete);
- unregulated;
- resistant to current surges;
- disconnected at a sharp increase in current.
There are devices that combine the functions of an RCD and a circuit breaker. Such devices are called differential automata.
Popular models
A specific RCD model is selected according to the technical specifications. If powerful electrical appliances are installed in the network, then the protective device must also comply with these parameters. Popular models include:
-
RCD 4P 63A 30mA Energy - device with 4 poles and electromagnetic disconnecting device. The rated current consumption is 63 A, and the minimum leakage current is 30 mA. Mounts on a DIN rail using a two-position clip. - UZO THZ 4P AC Legrand type is a differential current switch from French manufacturers. It is an AC type and responds to differential alternating current. It has the ability to install additional protective elements.
- ABB C40 / 0.3 - protection device for normal current operation. Differs in low price and good quality. Rated current in the circuit - 40 A, leakage - 300 mA.
To protect against overvoltage and short-circuit current, RCDs in the circuit are installed in conjunction with circuit breakers.
Electrical connection
Before connecting the RCD to a three-phase network, you must select the correct circuit. There are several ready-made ways to install the device in an electrical circuit. The connection diagram of the protective device is carried out in order to disconnect the entire electrical network in a country house or apartment.
With this connection, any damage to the circuit will shut down the instrument. The electrical device is located directly next to the electrical panel and meter. It can be hidden from external influences in a separate metal or plastic case. There is another way of arranging protective equipment.
It is possible to divide the electrical network into several sections and equip each with a residual current device. This scheme allows you to isolate and secure powerful household appliances. This scheme differs in that in an emergency, only one section is turned off, and the rest of the circuits will remain operational.
They usually share a bathroom, garage, basement and each floor in a country house. With this connection, the electrical network can withstand almost any load. The device itself is connected according to the designated terminals. Usually, on a 4-pole machine, a neutral wire is connected to the extreme right terminal, and phase conductors are alternately connected to the rest.
Phase wires are connected to a three-pole device, and the zero cable is connected to consumers through a separate bar. The performance of the RCD is checked using a special test button. If the electrical circuit breaks when pressed, then the connection is correct.
