What is an RCD: working principle, device types and marking + which you need RCD

Any electrical network must have a safety device, but that is the RCD and a principle of its operation knows not everyone. Deciphering abbreviations is as follows - residual current device.

This low-voltage electrical apparatus designed for switching off the protected circuit portion when creating a differential current exceeding the rated value for this device.

This article will try to analyze in detail the device and operation of the RCD, to consider existing varieties and to deal with the kind of information includes the protective device off.

Purpose of protection device

Grounding device RCD circuit PE is neutral conductor or conductive housings of electric resistance mechanisms parts with not greater than 4 ohms.

In can be energized occurrence of leakage current these items of equipment that It poses a risk to human life and animals in contact with them, as well as to property generally.

Save from an electric shock - calling the review apparatus. Upon detection of the leakage current are turned off voltage.

The greatest danger lies in the fact that such violations in the chain are invisible and rarely noticeable when at the touch of the instrument can feel a slight electric shock.

The main cause of this phenomenon is the contravention wiring insulating layer. Uncontrolled processes can cause great harm, so protective equipment becomes more popular in the domestic environment.

The use of an RCD is most prevalent in single-phase networks with alternating current and grounding the neutral line, and a voltage up to 1 kW indicators in a format domestic electricity supply.

The design of the RCD

Optional features of the protective mechanism will help to understand the principle of the RCD action, namely reproducible reaction unit to the current leakage.

The key operating sites are:

• Transformer differential sensor;
• Starting bodies - the mechanism Tearing properly functioning electric circuit;
• electromagnetic relay;
• control unit.

Counter connected to the sensor coil - and zero phase. In normal network operation, the semiconductor elements formed in the core magnetic flux having opposite direction in relation to each other. Due to this magnetic flux is zero.

To a secondary winding wound on the magnetic core of the transformer is connected type electromagnetic relay. If you met the standard working conditions, it is not involved in the network.

all work is changing dramatically when leakage occurs. The phase and neutral conductors are beginning to pass different current values. Now the value of the force and direction of magnetic flux in the transformer core will also have different parameters.

It appears in the secondary windings when the current and predetermined values, reproduced tripping electromagnetic relay. It is connected in tandem with the trip mechanism. This ligament in the right moment and responds disengages the grid.

Check node is represented by resistance mechanism - a certain load connected to bypass the differential sensor. This element simulates the leakage current and thus checks the operating condition. More we talked about validation methods in this article.

Action / RCD operation principle is as follows: the current supply line in phase with the reference resistance, and after that - to the neutral wire, bypassing sensor.

Thus, the conditions of different indicators of current input and output device. This imbalance and should lead to the launch of off site.

Depending on the development, schematic device can vary, but the principle used in the RCD, is identical in all models.

The principle of operation of the protective mechanism

Consider what you want to use an RCD. The functioning of the protective device based on the measuring method.

Fixed parameters of the incoming and outgoing currents flowing through the transformer. If the first value is greater than the second, which means that the electrical circuit occurs the leakage current and the instrument plays off. If the parameters are identical, the device does not work.

For a better understanding, let us consider how to work the RCD in the household distribution panel with a two-pole system.

To the upper terminal blocks connected to the input two-wire line (phase and neutral). To the lower terminal blocks connected phase and zero padded up to a load portion, e.g., to an outlet of the boiler or the power kettle. protective earthing device will run the cable, bypassing the RCD.

In the standard operating mode, movement of electrons is performed on the phase line from the incoming cable to the electric heater of the boiler / kettle flowing through the differential protection unit. They move back to the ground again through the RCD, but the line-to-neutral.

For example, the insulation has been damaged appliance PETN. Thus, through the water that is inside, the current will be conducted partly housing, and then go into the ground through the wiring protective device.

Residues current return on the neutral line through the RCD. However, its power will be reduced by the amount of leakage compared with incoming.

Difference indicators calculates the differential transformer. If the figure is higher resolution, the device instantly reacts and breaks the circuit.

In another article, we have given our recommendations on the selection and proper connection RCD for boiler.

The feasibility of using the RCD

Consider, for which you want to use and RCD from any negative factors impact device provides protection.

First of all - the closure phase on the electrical enclosure. Basically to problem areas include heating elements heaters and washing machines. It should be noted that the breakdown is formed only in the case where the heat generating part is heated by the current.

Also, if incorrect wiring. For example, if used without twisting the terminal box, which are subsequently recessed in the wall plaster and closed. Since the surface has an increased moisture content, this will breakdown and twisted giving a leak in the wall.

Differential protective mechanism in this case will always perform blackout line portion until completely dry or until a rebuilt connector assembly.

Scope of the review of devices is quite varied - from public buildings to large-scale enterprises. They are equipped with electrical structures and circuits for reception and distribution: shields in homes, current supply systems for individual consumption, etc. The main thing with etoom - correctly select the RCD power.

Types of devices and their classification

Firms developers endow their products with diverse features that must be considered in determining the right type of RCD, building on the specific operating conditions conductive network.

To an ordinary consumer was able to pick up the necessary residual current device among diversity of the proposed models, classifying system was created based on the following characteristics:

• operation principle;
• kind of differential current;
• time delay tripping of the differential current;
• number of poles;
• installation method.

Next, let us consider in more detail each of these classifications.

Classification # 1 - by inclusion method

There are only two switching method - electromechanical and electronic. In the first case, the machine will shut off power to the damaged line, regardless of the mains voltage. The main working body - toroidal core with windings.

In the formation of leakage in the secondary circuit formed by the voltage for activating the operation of the polarization switch, which leads to the activation of switch mechanism.

The functioning of the device in the electronics depends entirely on the additional stress that is external power required. Here, the working body is represented by an electronic board with an amplifier.

Within such a mechanism there are no additional sources of accumulating energy, so the operation of the circuit uses electricity and the external network, if there is no voltage, - the device does not break the chain.

An example operation of an electronic RCD, an on-line with the socket, is fed from a microwave: breakage occurred zero phase, in addition to this, in the same period, malfunction of the microwave is formed and wiring occurs phase ground fault, i.e. it appears dangerous potential.

If you touch the stove, electronic security type will not be used because No power supply. It is because of insecurity in comparison to electromechanical analogue of this device was less common.

Classification # 2 - leakage current of the genus

All models are manufactured security automata further divided by the load current passing through the device. They are treated with a predetermined format voltage fluctuations.

In the case of all devices in the passport prescribed nominal value of the operating voltage. This parameter should match the range of the nominal electrical current.

AU type will be activated upon occurrence of instantaneous AC voltage controlled leakage circuit or when its capacity undulating. These devices are marked with the inscription "AC" or symbolic sign "~".

Type A is triggered when the instantaneous formation of alternating or pulsating current breakdown in a controlled circuit, or with their slow increase.

This mechanism can be used in any view of the situation. On the housing of the machine applied to the abbreviation "A" or symbol as in the graphic image in a rectangle .

In most cases, the A-type is connected to the circuit, where the load regulation is reproduced by cutting the tops sine wave, for example, the adjustment parameters of the engine revolving speed movements thyristor converter.

The RCD subspecies effective for playback in the subject reaction wiring DC, AC or converted (rectified) leakage current.

This is expensive equipment designed for industrial activity sites. In a domestic environment, they do not apply.

Presented disconnection protection device types A, B and AC were calculated for the period from the activation of 0.02-0.03.

Classification # 3 - for the time delay type

This classification involves the distinction of two types: S and G. Automatic protection type can be characterized by reacting S selective format. Exposure of the response time corresponds to the range 0.15-0.5 seconds. It is advisable to select in the case of group connections RCD.

According to the scheme, in the panel taken two load groups in the form of sockets and №1 №2, which is connected RCD type A, and the input of the second machine space - S.

If there is a breakdown in one beam, the opening device is activated only when a collective unit does not perform its function and shuts down the defective portion.

Selectivity open circuit activation can be performed using another method - by setting the leakage current. This method is most prevalent.

Take analogous to the preceding scheme, and to modify it thus: a group select automatic type SS only has to set point diftoka 0.03 A, and is analogous to the device input only 0.1 A.

There are situations where residual current circuit damage exceeds the nominal setting of the two protection devices. For the first scheme selectivity will not be broken, and the second - the current cut-off can apply any of the connected devices.

Apparatus form factor G is also represented drawdown selective principle and has a shutter 0.06-0.08. All these sample types are designed to withstand extreme currents - up to 15 kA.

The current limit is an important parameter of choice, because It is due to this and ensured security.

For example, in environments with high humidity, electrical power is supplied in connection with trip devices circuit with setpoint 0.01 A. For standard household conditions - 0.03 A.

For fire safety organizations buildings - 0.1-0.3 A. We encourage you to read tips choice of fire RCD and the intricacies of its installation.

Classification # 4 - the number of poles

Since the automatic device operates by comparing the current values ​​passing through it, the number of poles in the machine is identical to the number of conductive lines.

Pole RCD referred to as 2P. It includes a single-phase circuit to ensure the protection of man and the prevention of possible causes of the fire.

Marking four-RCD - 4P. They are designed to work in a network with three phases. It is also possible setting combinations, e.g., the device with four poles is introduced into the two-wire network.

However, it is not implemented the full potential of the device, which is economically disadvantageous.

Classification # 5 - method of installation of the device

Since differential protective devices are performed in different housings, they can be used as a stationary or portable.

In the second case, the machine is equipped with extendable wire. Devices are fixed to the din-rail, mounted in a switchboardThat is placed either in the corridor or in the apartment.

There is also a kind of performance options RCD-socket and RCD-plug. Both in the first and in the second case an appliance and connected by a mechanism at break is not dangerous for humans.

Full transcript labeling values

It is mandatory on the device is present name of the company-developer. This is followed by a standardized marking the designation of the serial number.

To decipher the abbreviations we use an example [F] [X] 00 [X] - [XX]:

• [F] - a disconnecting device;
• [X] - execution format;
• 00 - numeric or alphanumeric designation of the series;
• [X] - the number of poles: 2 or 4;
• [XX] - characteristics of the leakage current view: AC, A and B.

Also, there will be indicated and the nominal parameters of the device, which in the selection should pay special attention.

For maximum parameters, which are designed devices include voltage Un, current In, The differential value circuit breaking current IΔnThe ability to enable and disable im, switching capacity with closures Icn.

Basic labeling values ​​must be arranged so as to remain visible after installation of the device. Some parameters can be applied to the side or at the rear, visible only to the product installation.

Outputs intended only for connecting the neutral conductor, denoted by the symbol of the Latin "N». RCD to trip mode indicated by the symbol "ABOUT"(Circle) included - short vertical line"I».

Not every product marked optimum temperature environmental indicators. In those models, which is a symbol  - This means that the operating range of -25 to + 40 ° C, unless there is no designation - refers to the standard values ​​from -5 to +40 ° C.

Conclusions and useful videos on the topic

Footage detailed overview of all the constituent elements review protection mechanisms, their purpose and the principle of interaction with each other:

A description of all types of circuit breakers, as well as advice on how to make a choice:

The answer to the age-old question, on what to choose - at the differential machine, or to the RCD + mounting secrets:

Use of RCDs - a profitable and correct decision not only on the part of economy, but, in terms of fire safety and protection of man.

It is recommended to use the maximum of its potential in the domestic environment by installing all the electrical engineering group to provide complete isolation from the impact of electricity.

Still have questions on the principle of action or classification circuit breakers? Or do you want to supplement the material described useful information? Please write your comments in the block clarification, ask questions - competent experts and visitors to our site will try to answer you maximized.