RCD: what is it? Purpose, application and technical data

The requirement for reliable protection of the person from the harmful effects of electric current always ahead of the potential of science and technology to create security devices that meet this goal. Today, innovations in the electrical industry to fully meet all the criteria for this type of devices. The article reveals the question of how such a device, the RCD: what it is, its purpose, the principle of action, the selection and application.

Means and methods of electrical protection: modern devices and the characteristics of their work

As soon as the application of electrical current came into our lives, once there was a need for protection from its damaging effects on human health. First of all - is the fulfillment of the insulation of conductive parts of the wiring and components of the current receivers.

But complete isolation is impossible, as in any electrical circuit there are technology gaps and contact groups. There is always a possibility of an abnormality (failure) of the insulating layer and the conductive elements of mechanical damage, and most importantly - statistical regularity in violation of safety regulations and rules of operation of electrical equipment, both on the production and household level.

Electrical protection: insulation and earthing

One of the most effective ways to protect against the damaging effects of electric current is the organization of the ground loop. ground loop - this artificial compounds having "ground" (so-called PE-conductor) neutral conductive housings or parts of electric mechanisms having a resistance no greater than 4 ohms. These electrical elements may be energized because of the earthing phase conductor or lightning current.

The main purpose of the device ground loop - this eliminate the possibility of defeat of a human or animal an electric shock in the case of touching the body or parts of electrical equipment mechanism be energized due to the closure phase in which the electric current.

Note! The AC networks with a grounded neutral point and the voltage to 1 kV (this housing electrical format) in the ground As primary protection against electric shock indirect contact is not applicable, since it is not effective.

The problem of the most efficient protection against electrical effects on humans decided to so-called device differential current (UDT) - a large segment of the control and protection devices for different purposes and design features. Classification UDT segment quite extensive from the control method, the type of installation and the number of poles, and to the possibility of regulating the time delay tripping of the differential current.

Consider what the RCD. Deciphering this abbreviation - residual current device. Requirements for the installation and use of UDT are shown in enlarged edition of the SAE - installation rules electrical equipment and a series of standards for electrical installations of buildings IEC 60364, and the impact of current on human beings and cattle IEC 60479-1.

Historical background RCD development

A pioneer in the development of the RCD was Germany. The first working model of the protection device has been designed and built in the thirties of the last century. As the leakage current detector it uses the minimum possible size of differential current transformer, and the control element polarized magnetic relays used with a sensitivity of 100 milliamperes (mA) and a speed of not more than 0.1 seconds.

fixing the differential current threshold at the prototype was about 80 mA. Develop a monitoring relay with a sensitivity of less than 80 mA at that time it was not possible due to lack of materials with the desired electromagnetic characteristics. It was only in the mid-twentieth century, it was suggested new design RCD. The design took into account the mechanisms to eliminate false positives from discharges during a thunderstorm and a weight increased sensitivity residual current up to 30 mA.

We have also undergone changes and dimensions RCD: the size of the shipping carton to a modern format that can be mounted on DIN-rail in modern electrical cabinets.

Technical experts in the field of electrical and electronic developments are already making predictions for the future. They firmly believe that soon such systems as protection against electric shock will manage artificial intelligence.

He will be able to perform not only measurement and control functions, but also carrying out video and audio monitoring given to him by the object, to make instant decisions on any random situations and, if necessary, notify service salvation.

RCD: what it is and how it works

Among the most popular of the protective UDT working in a domestic environment, are protective device (RCD). RCD works like human protector against electrical shock and as a preventive mechanism to prevent accidental ignition wiring cables and electrical cords plug.

The functional idea of ​​this device is based on the laws of electrical engineering, postulating the equality of the incoming and outgoing current in closed circuits with active loads.

This means that the current flowing through the phase conductor must be equal to the current flowing through the neutral conductor - for single-phase AC circuits at two-wire wiring, and the current in the neutral conductor must be equal to the sum of currents which flow in the phases for phase four chain.

When such a circuit due to accidental contact person uninsulated portions of the conductive circuit elements or contact the exposed portion of wiring (because damage) to other conductive material, forming a new electrical circuit, there is a so-called current leak - equality of incoming and outgoing currents violated.

This disorder can be registered and used as a command for disabling the entire circuit. In this process, and it was designed RCD. A current of "leakage" in the electrical steel called differential current.

RCD can detect very low current "leaks" and perform the switch mechanism function. Theoretically RCD operating principle is as follows (where I_Rin - input current of the neutral conductor, I_O - output current of the phase conductor)

• I_Rin = I_O (Balance of the system without disturbing, the RCD in the idle state);
• I_Rin > I_O (Balance of the system is broken, the RCD detects the appearance of residual current and disconnect the mains supply).

RCD mandatory defense

When the electricity network installed RCD, which means that provide protection from:

• circuiting the phase conductor to the housing of the appliance. In a lot of cases - is the heating elements of washing machines, water heaters and space heaters. Moreover, breakdown can occur only when the thermal element heats up under the action current;
• incorrect wiring, when unscrupulous electricians immure in plaster "twist" wires without back box. If the wall is wet - this twist differential current leakage will occur in the wall all the time and the RCD will de-energize the line until completely dried plaster or the right will be repaired compounds;

• incorrect installation in the switch box when seemingly small, but "good" change, introduced into the circuit, changing the current distribution and lead to a loss of high performance device. This will be discussed in more detail a little later.

RCD may be triggered for reasons not evident at first inspection appliance connection scheme. If you use a gas stove with an electric gas burning down or the washing machine hose is connected to the metal housing to the water tap or when neighbors produced on ground or water heating system, whereas in the circuit current leakage will occur again, due to which the fire is RCD. In such cases, a thorough engineering analysis.

Boundary conditions RCD work

The rules are often exceptions. This principle is not bypassed and the generic quality of the device under consideration breaker.

RCD not react when a person or an animal comes under tension, but the earth fault current is not going to happen. This case is possible when touched simultaneously to the phase and neutral conductor, under the control of the RCD, or total isolation from the floor. RCD protection in such cases, is completely absent. RCDs can not distinguish between an electric current passing through the human or animal body from a current flowing in the load element. In such cases security can provide for mechanical protection action (full isolation dielectric housings and others.) Or complete blackout appliance before inspection.

RCD, completely dependent on the supply voltage to the appropriate network entity, is operational only in case of full serviceability of said network. The situation can become dangerous when the "above" the RCD will open neutral conductor and phase conductor will remain energized. Then in the wiring phase conductor may be a factor in the risk of electric shock and RCD because of his own disability will not be able to turn off the power supply.

RCD can "freeze" in the standby state, if there is a blockage in the main contact shaft solenoid or failure of the secondary winding of the control device, and at the right time not work. In order to check the operating state exists RCD test mechanism. If you regularly carry out a test scan of the device (and for this, simply press the "T" - test), the risk of damage to the RCD will have a minimum probability.

The use and how to connect the RCD

The main use in a domestic environment RCD obtained using electrical groups of bathrooms, kitchens and rosette groups a large number of connected devices and the equipment. This does not mean that the use of RCD in the total incoming network does not make sense. This sampling scheme is dictated by only the operational management and marketing feasibility, as RCD small currents are much cheaper in price with higher power devices.

However, in some cases, if we consider hostels, clubs, etc., will be a reliable application of the general selective RCD because of the mass and the simultaneous use of almost all the elements of the electrical equipment. RCD selective type different from conventional high latency residual operating current (i.e., response time) and is one of the most used devices. When triggered, the usual local RCD in any circuit, overall selective RCD does not disconnect all wiring once, and allows the power supply to stop only a particular group.

For example, if a disco an insulation of equipment and the body (for example - the amplifier) ​​will be in contact with the phase conductor, in the moment of contact of the amplifier by the operator, the local RCD It works on and off only group amplifying equipment, and overall selective RCD is not shut off all the power, and groups such as ambient light, the toilets and the cafe will operate in standard mode.

a mechanism to connect the RCD in existing network similar to the connection of the circuit breaker, with the only difference being that when a single-phase machine Tightening the two terminals, on the RCD - four.

If you touch the man bare plot wire or equipment case under phase voltage, instantaneous power outage - so RCD tripped.

Important!The AC systems additional protection by the RCD to be provided for the sockets groups with rated current up to 20A (washing machines, boiler, Ovens, etc..) And mobile (portable) equipment and power up to a rated current 32A that is used outdoors.

Basic principles of RCD mechanism and a comparative analysis of analogues

Physical processes in the mechanisms of the work of many modern electromechanical or electronic devices, can be us completely understandable. Not everyone has the knowledge of engineering disciplines and, of course, not be able to understand and describe the physical basis of the principles of operation of a device. But the principle of use (operating rules), built on the security features, enables the use of the most sophisticated inventions in our daily lives.

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Each instrument has a technical passport, which easily understood language is always described and purpose, and principle and, whenever required, there are prescribed activities for installation, connection and correct operation. In our case, it was an attempt to describe the principle of the disconnection protection device (RCD), the most affordable way and give the reader an opportunity to make decisions in the choice of one or the other device in the case needed.

The operating principle of the RCD and the design features

To fulfill its protective function, the apparatus includes a minimized size of differential current transformer control "follower" magnetoelectric relay solenoid control the main contact group, and additional diagnostic elements - "Test" button and the machine elements operation.

The physical side of the work is as follows.

When the RCD (push button contact closure) is activated solenoid and hold the contact group is similar to the electromagnet rod. Since that moment come into contact terminals of the solenoid coil and terminal power supply wires. But in the scheme of the solenoid power installed transit contacts opening, which are controlled by magneto switches and relays is given the function of self-disconnection RCD.

The outgoing and incoming mains current flowing in respective windings of the transformer, due to the generated emf (Electromotive force) creates two equal but divergent magnetic in the magnetic core (core) flow.

Due to the full compensation of magnetic fluxes in the wound on the secondary side, the supply control switch, there is no electromotive force and the relay is passive.

At the moment of the contact person or animal bare part of the phase conductor or the housing of a household appliance, on which occurred breakdown phase, through incoming transformer winding would proceed an additional differential current.

Violation of the equality of incoming and outgoing currents instantaneously create uncompensated magnetic flux in the transformer core. As a consequence, the instant appearance of EMF in the secondary winding coupled with the relay as the source of his power.

Relays, received power, immediately triggered and disconnects power solenoid (transit terminals open), holding the main contacts in the closed position.

Contacts open, the solenoid is de-energized and releases the spring-loaded rod of the contact group, and network power supply is interrupted. The more sensitive control relay to small values ​​of differential current, the more effective protective function RCD.

Note! These protection functions such as power failure with symptoms of short-circuit and overcurrent in the RCD are not provided. In practice, the installation of RCDs usually involves the joint use of the circuit breaker ( "machine"), calculated directly on the possibility of short-circuit and overcurrent.

The correct wiring diagram and automatic RCD. errors of fitting

Both devices have the same support structure for installation in the control flaps accounting and distribution of electricity. The problem is reduced only to the correct connection to the mains and to each other:

1. Basic option: central automatic accounting counter → → RCD.
2. Preferred: central automatic accounting counter → → → selective type RCD group automatic → group RCD.

In this case shows the recommended sequence of connections, but also need to consider the most correct wiring diagram:

• in any case, do not connect the neutral wire to the ground terminal after it exits the RCD. In this case, the possible occurrence periodic differential leakage current, resulting in false positives;
• not a complete phase connection RCD. If the neutral wire from the mains will pass in transit by the RCD, the resulting current in the neutral wire will be perceived as a differential that will lead to permanent tripping device;
• not to allow the connection of zero wire outlets controlled by RCD, with the wire (terminal) ground. However, even unconnected to the consumer outlet will create a differential current;
• for group use of RCDs are not allowed on the bridge the neutral conductor outside the terminals. This will lead to the triggering of the RCD at the same time.

Useful advice! When you connect the four-pole. those. three-phase RCD in the same network must be strict compliance with the phase-coded labeling Terminal device. Otherwise, the test mode will not be objective.

RCD analogs with enhanced features

Market UDT (residual current devices) are very diverse. It should be isolated from a number of competing with counterparts RCD called differential machine, belonging to the class of circuit breakers, residual current-driven - RCBOs.

To answer in simple terms to the question: Emergency circuit breakers, what is it? - you must remember that its main feature is the combination of a main function of the RCD and circuit breaker. Also, the difference of the differential RCD and machine is that most need RCD protection against short circuits in the network and current overloads (of course, for this purpose, and is set in a pair of circuit breaker) and Emergency circuit breakers capable of defending itself themselves.

It is worth noting the entry of new models of RCBOs - electronic and with auxiliary power supply. They differ from electromechanical designs presence of the electronic board with the differential current amplifier, which allows fix the leaks and about 10 mA even when triggered neutral wire breakage incoming network when the phase wire remains under voltage. Conventional RCDs or RCBOs in a situation in contact with human open phase portion does not work.

Another novelty in the line of residual current devices - so-called multi-functional safety device. What it is USM becomes clear from the reference to its intended use. This device serves to shut off the equipment at the output of voltage parameters for the network operating limits (less than 180V and more than 260V), as well as for the protection of the operating equipment of the "burning" of the winding and the electronic components of devices surges. These spikes can be caused by electromagnetic pulse or closures at zero phase conductors in a three-phase network.

RCD or differential Machine: how to distinguish and to choose

There is no single algorithm, allowing to give preference to one or the other device does not exist. The reason for this particular choice mnogovariativnoy. The main factors that affect the selection of the RCD and RCBOs.

Is it possible to place one or the other device in the main panel. In practice - Overall total size of the RCD and circuit breaker longer than the overall size Emergency circuit breakers.

What is the purpose when you make changes to the electrical circuit. If necessary, individual protection high-power equipment (kitchen stove, boiler, washing machine, etc.) From a possible "hit" of electric shock, is optimized differential automatic, clearly keeping an eye on the load current.

In the case of the need for protection against electric shock for some group of sockets or lighting lines in which power can be increased over time, it is advisable to apply RCD. RCD has a large supply of power, and the differential machine in connection with transshipment need to replace more powerful.

qualitative assessment. Practice has proved that the devices combines many functions of different devices, very often inferior in quality to a single device. This also applies to devices such as a differential multifunctional machine that the quality and durability is inferior and the RCD circuit breaker.

The situation with the breakdown. In a situation where work is no longer the RCD or circuit breaker needs to be replaced, or one or the other device. But when the machine is not working differential, even by reason of failure of a certain function, it is necessary to replace it with a new one. In this case, the cost is much greater.

The stability of the power supply. Failure of the RCD, is sufficient to establish a jumper between the circuit breaker and the electric mains (bypass RCD) and a power supply is restored. But in case of breakage Emergency circuit breakers Emergency circuit breakers need or emergency or a spare circuit breaker. So most expeditious resumption of power supply may be in question.

Useful advice! If necessary, proper selection of the desired residual current device (RCD or RCBOs) if use engineering approach and economic assessment even when the hand already has some form of device.

There was a question on the external differences from the RCD RCBOs.

Marking the cover of the device. EXAMPLE 1: "ABB 16A 30 mA" - RCD ahead of us ABB (manufacturer company "ABB") with a nominal current of 16 amps and a lower differential current of 30 milliamperes. Example 2: «CHNT C16 0,03A" - Emergency circuit breakers in front of us, the manufacturer company CHNT c rated current of 16 amperes and the characteristic of the electromagnetic and thermal breaker class "C" in the differential current 30 milliamps.

Said wiring on the front side. For RCD is designated in Scheme differential transformer (oval loop), a control relay (square) with a loop on the contour of the oval and a test circuit in a chain line. Emergency circuit breakers for the scheme is very similar to the scheme of the RCD, but there are additional figures in the form of a small arc and line speed - this is the designation different from the RCD, electromagnetic and thermal breaker.

The use and installation of RCDs: designation in wiring diagram

The majority of control control devices installed in the electrical grid, have a small list of parameters necessary for the proper selection of the electrical circuit.

Selection is made for the RCD to the nominal load current threshold and locking differential leakage current. Practice recommends a value not exceeding 30 mA. Installing the RCD in the electrical network is based on an engineering analysis of existing network elements and assembly capabilities. Connection diagram RCD network should take into account all the possible switching errors and eliminate them. Only when the correct power supply circuit connected to the RCD will provide maximum efficiency for triggering protective mechanisms of the device.

Selection parameters and wiring diagram RCD without grounding

Knowing the principle of the RCD, the standard two-wire power provided only phase and neutral wires having no ground circuit, can and should be set RCD in accordance with the requirements of protection. The correct installation RCD circuit previously discussed.

The answer to the question of how to put the RCD in the apartment, is with a calculator in hand. It is necessary to sum the power units of the equipment and machinery installed in the apartment, and the amount divided by the number 220. Thus, a rough approximation we calculate the nominal current, and in which the choice will be made by the RCD. This calculation is based on a mathematical relationship of electric power from the mains voltage (220V) and current occurring when the power supply load devices:

M = U x I,

where M - power, U - voltage, I - current.

Example: RCD must select the group for protecting electrical kitchen unit. On this line, there is such appliances:

1. Electric oven 2000 watts.
2. Microwave 1200 Watts.
3. Food processor 700 watts.
4. Refrigerator 800 Watts.
5. Small appliances 600 watts.

Summarize wattages: 2000 + 1200 + 700 + 800 = 5300 watts. Calculates the current by the formula: I = M / U = 5300/220 = 24,09A. Choose the closest at par RCD with great value - 25A.

For in-depth calculation of the currents in the lines of wiring required basic knowledge of the highest electrical engineering.

In addition to the rated load current and differential current threshold of sensitivity, in some cases, when selecting an RCD is required to pay attention to another criterion - the category of the leakage current. It in most cases concerns the AC and pulse current in the network.

Category AC It assumes RCD work environment AC differential leakage. This category is the most common and can be used in all kinds of AC networks. In some cases triggered RCD - discussed above.

Category A It has the lowest detection limit (about 10 mA) of the differential current and is able to fix a separate component of the current amplitude (a so-called half-wave). RCDs with such categories leakage current responds not only to a variable current configuration, but on impulse. Such RCDs acquire priority application, as more and more household appliances, particularly lighting elements is converted into blocks of pulse current supply.

The main trend in the European market is the expansion of the segment pulse equipment. This naturally leads to an increase in number of pulse current applied RCD. But as in the domestic application of the active current receivers will remain for a long time (fully variable), RCD category AC will take quite a wide space on the market shelves.

Returning to the question of the absence or presence of electrical earthing circuit, it is necessary to emphasize the fact that even with available ground to an even greater degree of protection required by the organization of electric shock due to installation into the network RCD.

Basic principles of connection diagrams in a single phase RCD network has already been discussed earlier. Wiring Diagram RCD grounding is no different from the circuit without grounding.

Useful advice!If the grid has a ground circuit, it is necessary to control and ensure proper circuit when connecting RCD when any one neutral conductor wiring must not be coupled to the conductor (terminal) ground circuit.

Graphical symbol RCD in the scheme of power supply

The main legislative provisions entered into the GOST 2.755-87 ESKD "Graphical symbols in electrical circuits and contact switching device compound "and GOST 2.710-81 ESKD" alphanumeric designations in electrical circuits "prescribed graphic lettering and other devices such as RCD. But no strict requirements on the designation of different residual current device is not charged.

As we already know, all residual current devices presented breaker mechanism and control element - a differential current transformer. Therefore, designation of the RCD in the diagram is represented by two standard graphic symbols - the circuit breaker and the transformer differential current recording. You can see the graphic representation of the RCD on the single line diagram and other drawings.

Wiring diagram for three-phase RCDs

This type of device is commonly called chetyrohpolyusnym and specificity of its connection to the three-phase network is completely analogous to the bipolar connection RCD. On the device listed terminals connection of the phase conductors and the neutral conductor. Also attached to the device certificate, which presents a standard connection diagram in the three-phase four-pole RCD network.

Different manufacturers sometimes there are differences in the location of the zero terminal of the device - right or left, and the connection of the phase conductors only requires compliance with the marking at the entrance and output.

Three-phase four-pole RCDs are used for large differential leakage currents and their main purpose is only protection against ignition wiring. In order to organize the protection of people from electrical shock, it is necessary in each individual group Equipment to install single-phase two-pole RCD with adjustable leakage current equal to no more than 30 mA.

Lineup, manufacturers and prices RCD

UDT market products segment comprises a number of foreign brand-name companies as well as domestic producers. To date, preference is given to brands from Italy, Poland, Germany and Spain, as their products have received the best consumer assessment of the quality criteria of reliability and the relationship price quality. Existing market UDT residual current device allows for a wide range of various types of devices, providing a diverse range of goods both in price and quality.

The table lists the most common goods manufacturers UDT and shows the market prices offered by them:

product name	Trademark	price, rub.
RCD IEK VD1-63 single phase 25A 30 mA	IEK, China	442
RCD ABB single-phase 25A 30 mA	ABB, Italy	536
RCD ABB single-phase 40A 30 mA	ABB, Italy	740
RCDs Legrand 403000 single phase 25A 30 mA	Legrand, Poland	1177
RCDs Schneider 11450 single-phase 25A 30 mA	Schneider Electric, Spain	1431
IEK VD1-63 three-phase RCD 63A 100 mA	IEK, China	1491
Automatic switch IEK VA47-29 25A	IEK, China	92
Circuit-breaker 25A Legrand 404 028	Legrand, Poland	168
Circuit Breaker ABB S801C 25A single-pole	ABB, Italy	441
RCBOs IEK 34, three-phase C25 300 mA	IEK, China	1335

As can be seen from the comparative table price 25A RCD 30 mA (the most sought after on the market) depends on the manufacturer. So the price of ABB RCDs 25A 30 mA higher than Chinese counterparts, but lower than that of manufacturers such as Legrand and Schneider Electric. Taking into account criteria such as quality and value buy RCD 25A 30mA preferred company ABB, and the necessary circuit breaker can buy Chinese-made or company Legrand.

Useful advice! Having made the decision to install the RCD in the home network, but not having experience in similar wiring devices, use the services of a qualified electrician.

Summing up this excursion into the world of the residual current devices, in particular - a residual current device (RCD) will focus on the important points discussed.

One of the most effective means to protect humans and animals against the damaging effects of an electric current is to install a network of the electricity supply circuit breakers - RCD.

RCD has a function to respond to the differential leakage current, which appears on contact with the exposed part of the person posting or body of any electrical equipment. It may be under a phase voltage due to damage to the insulation of the phase conductor and the contact with the body. RCD also responds to current leakage between the wiring insulation fault when it can lead to heat and fire.

However, the RCD does not respond to the phenomenon of short circuit in the wiring circuit and excess capacity in the current chain. In this connection it is necessary to install the device in a pair with the circuit breaker ( "automatic"), which responds to short-circuit and overload power.

Most importantly - always follow the safety rules and caution when working with power tools and appliances. How can often produce a visual inspection of the open current-carrying elements of Electricity and plug elements for the current collectors.