The principle of operation of the bond. RCD: operating principle, purpose, technical characteristics, RCD connection options

A residual current device, further referred to as an RCD, is designed to protect a person from electric shock, as well as from a fire that can occur when an electric current leaks due to poor insulation or poor connection of electrical installations (EU).

The RCD should operate, that is, open the contacts, thereby completely stopping the supply of voltage to the protected line, provided:

1 Human contact with non-current-carrying parts of the power plant that are energized due to insulation breakdown.
2 Human contact with live parts of the power plant that are energized.
3 Occurrence of (differential) leakage current to the power plant housing or ground to prevent fire.

Operating principle of RCD. Scheme

Rice. 1

1 Differential current transformer
2 Trigger element
3 Actuating mechanism
4 “Test” button to check the serviceability of the RCD
I 1 – I 2 direction of current relative to load
I D – leakage current
Ф 1 – Ф 2 magnetic fluxes

Purpose of blocks.
1 Differential current transformer(used in most RCDs) measures the balance of currents between the conductors entering it.
2 Trigger element(consists, as a rule, of electromagnetic relays) serves to control (influence) the actuator.
3 Actuating mechanism Designed for emergency shutdown of an electrical circuit controlled by an RCD.
4 “Test” button to monitor the serviceability of the RCD by creating a leakage current simulation.

Operating principle of residual current device (RCD)

Electrical circuit diagram

Rice. 2

1, 2 Primary windings
3 Secondary winding

If the controlled line is in good condition, there is no specified leakage current, and the transformer is in a state of rest (equilibrium), because the currents in the oppositely connected primary windings of the transformer are equal. Due to the fact that equal magnetic fluxes moving towards each other are mutually subtracted (that is, equal to zero), no electromagnetic field arises in the secondary coil, which means there is no voltage and no emf arises capable of influencing the relay on the basis of which the trigger mechanism is assembled (Fig. .1 ).

And as soon as a leak occurs on the protected (controlled) line equal to the RCD response value (usually from 10 to 30 mA), then the equality in the primary windings of the transformer is violated. As a result, an electromagnetic field arises in the primary and secondary coils, which forms a voltage coupling. That is, in the secondary winding a relay operating voltage arises (Fig. 2), which makes up the starting element (Fig. 1), the effect of which on the actuator (Fig. 1) turns off the contact group, thus de-energizing the protected line.

Attention!

It should be remembered that the RCD requires monthly testing, which is carried out by pressing the “Test” button. In this case, the electrical circuit closes, emitting an artificial current leakage and triggering the protective shutdown device. Failure to operate will indicate a complete malfunction of the device.

According to modern requirements, all electrical installations must have or. In this case, a specified leak that occurs will automatically disable the protection.

An example of this can be seen in the diagram in Fig. 3

Rice. 3

If we imagine differential protection in the form of a simple mechanical device like a scale (Fig. 4) with a response threshold of up to 10 mA. It immediately becomes clear that when the value of 10 mA is reached on one of the scales, they will go out of balance, the contacts will open and the controlled (protected) line will be de-energized. Moreover, we note that the center of balance of the scales is precisely or, therefore it is they that must be used so that the person himself is not this center.

Attention!

You also need to understand that the RCD is an additional safety measure that responds only to differential current (leakage current) and does not respond to short circuits and line overload. Therefore, as a rule, RCDs are installed together with circuit breakers that respond to short circuits (short circuits) and line overloads for which they are designed.

Visual electrical diagram for connecting an RCD

Rice. 5

RCD. Video explanation

Selecting an electromechanical RCD

I wish you successful installation and remember electrical safety.

DIFFERENTIAL SWITCHES type VD1-63 (UZO). Manual

Passport

3421-033-18461115-2007 RE, PS

1 Purpose and scope

1.1 Automatic switches controlled by differential current, without built-in overcurrent protection, functionally independent of the network voltage for household and similar applications, type VD1-63 (UZO) of the IEK® trademark (hereinafter referred to as VD) are intended for operation in single-phase or three-phase AC electrical networks current voltage up to 400 V frequency 50 Hz

and their characteristics correspond to GOST R 51326.1 and technical specifications TU 3421 -033-18461115-2002.

1.2 VDs perform the function of detecting differential current, comparing it with the value of the differential operating current and disconnecting the protected circuit in the case when the differential current exceeds this value. VD provide:

— protection of people from electric shock through indirect contact with accessible conductive parts of electrical installations in the event of insulation damage (VD with a rated differential current of 10, 30 and 100 mA);

— protection against fires arising as a result of fire insulation of live parts of electrical appliances from differential (residual) current to ground or due to prolonged flow of damage current in the event of failure of overcurrent protection devices (VD with a rated disconnecting differential current I D n = 300 mA);

— VDs having a rated differential switching current of no more than 30 mA can be used as a means of additional protection in the event of failure of devices designed to protect against electric shock.

1.3 The main area of use of VD is accounting and distribution boards of residential and public buildings, temporary power supply devices for construction sites, garden houses, garages, retail facilities.

2 Main characteristics

2.1 The main characteristics of the VD are given in Table 1.

Table 1

Characteristic name	Meaning
Number of poles	2	4
Rated operating voltage Ue, V	230	230, 400
Rated network frequency, Hz	50
Operating voltage range of the operational monitoring device, V	from 115 to 265		from 200 to 460
Rated current In, A	16, 25, 32, 40, 50, 63, 80, 100
Rated residual current I D n, mA	10, 30, 100, 300
Rated non-tripping differential current I D n o , mA	0.5 I D n
Rated maximum making and breaking capacity Inm, A	1000
Rated maximum differential making and breaking capacity I D m , A	1000
Rated conditional short circuit current not less than, A	3000
Rated conditional differential short-circuit current I nc, not less, A	3000
Characteristics of operation in the presence of differential current with a DC component, type	AC
Electrical wear resistance, on-off cycles (O-O), not less	4000
Mechanical wear resistance of B-0 cycles, not less	10 000
Maximum cross-section of the wire connected to the power terminals, mm 2	50
Presence of precious metals, silver, g	0.25 (per contact)
Climatic modification and placement category according to GOST 15150	UHL14
Degree of protection according to GOST 14254	IP20
Service life, at least, years	15

2.2 The values of the maximum HP shutdown time in the presence of differential current are given in Table 2.

table 2

Attention! The VD does not have built-in overcurrent protection, so it is necessary to connect in series with it a circuit breaker of the same or lower rating with type B and C overcurrent protection characteristics.

2.3 Overall and installation dimensions are shown in Figure 1.

2.4 Electrical circuit diagrams of the VD are shown in Figures 2 and 3.

2.5 The use of VD in apartment and floor switchboards in electrical installations with grounding systems TN-S, TN-C-S, TN-C is regulated in GOST R 51628.

3 Completeness

Package Included:

VD - 1 piece;
packing box - 1 pc.;
instruction manual and passport - 1 copy.

4 Installation and operation

4.1 Installation, connection and commissioning of the HP must be carried out only by qualified electrical personnel.

4.2 The VD is installed on a 35 mm wide mounting rail (DIN rail) in electrical panels with a degree of protection in accordance with GOST 14254 of at least IP30.

4.3 After installation and checking its correctness, apply mains voltage to the electrical installation and turn on the high-pressure motor by moving the control handle to the “I” - “ON” position, press the button

"TEST". Immediate operation of the VD (switching off the circuit protected by the device) means that the VD is operational.

4.4 If, after turning on the HP, it turns off immediately or after some time, it is necessary to determine the type of malfunction in the electrical installation in the following order:

a) cock the HP using the control handle. If the VD is cocked,

this means that there was a current leak to the ground in the electrical installation caused by an unstable or short-term insulation failure. Check the operation of the HP by pressing the “TEST” button;

b) if the air pressure is not cocked,

this means that in the electrical installation there is a defect in the insulation of any electrical receiver, electrical wiring, installation conductors of the electrical panel or the VD is faulty.

In this case, you need to do the following:

— turn off all electrical receivers and cock the HP. If the HP is cocked, this indicates the presence of an electrical receiver with damaged insulation. The malfunction is detected by connecting electrical receivers in series until the VD is triggered. The damaged electrical receiver must be disconnected. Check the operation of the HP by pressing the “TEST” button;

— if the HP continues to operate when the electrical receivers are turned off, it is necessary to call a qualified electrician to determine the nature of the damage to the electrical installation or identify the HP malfunction.

The test is carried out by pressing the “TEST” button. Immediate activation of the high pressure motor and shutdown of the protected electrical installation means that the high pressure motor is in good working order.

How to understand what leakage current is

A leakage current occurs when an insulation breakdown occurs on the housing (the wire is frayed, the heating element is “broken,” etc.). A leak is when you touch the body of a device that is energized. You touched with one hand and at the same time you are standing on a conductive floor without shoes or touching some other grounded object (central heating radiators, for example). Current will flow through your body, and it will “go” through the ground loop, since this is the path of least resistance. This will be the “workaround” path. As a result, the “returned” current will be less and the relay on the RCD will operate.

But, pay attention! Direct contact immediately with phase and zero is not our case. In this case, the body is perceived as a load rather than a leak. This is a normal situation and the protection will not work. Therefore, work with electricity with one hand, wearing dielectric shoes. And never touch zero and phase at once.

Connecting an RCD to the circuit increases safety. This is especially true for wet areas such as a bathroom.

Sometimes the protection reacts to unobvious things: neighbors are grounded in the wrong direction, a stove with piezo ignition is not grounded, a washing machine or dishwasher is connected with a metal braided hose to metal pipes. In general, there are many situations in which leakage current is generated. These are all also leakage currents, but they are the result of errors or violations. And the RCD also reacts to them. If outages occur for no apparent reason, they simply need to be identified. It’s not easy, but you shouldn’t ignore “false” shutdowns. The reason may be dangerous.

What does it look like

There is a switch on the front panel of the RCD that can be used to manually break the circuit or bring the device into working condition. There is also a “Test” button on the front panel, designed to test the functionality of the protection device. When it is pressed, a circuit containing a resistor is connected, which emits the occurrence of a leak. If the device is working properly, it will turn off the power - the “switch” will move down, opening the contact.

There are sockets for connecting wires at the top and bottom of the device. The wires supplying power are connected at the top, and the lines that go to the load or to downstream devices are connected at the bottom. Both phase wires and zero (neutral) pass through the RCD. That is, when triggered, the power is turned off completely.

There are inscriptions on the case that reflect the main parameters. The RCD is mounted on a DIN rail; for this purpose, there are special protrusions on the rear surface of the case. Fixation methods depend on the manufacturer. There are models that are simply hung, and others with fixation using a pressure valve.

How to ensure quality protection

Despite the obvious benefits of RCDs, you cannot do without a circuit breaker. The RCD does not respond to overcurrents (short circuits) or overload. It only monitors leakage current. So for the safety of the wiring, an automatic machine is also needed. This pair - an automatic machine and an RCD - is placed at the entrance. The machine is usually located before the meter, leakage protection is after.

Instead of a pair - RCD + automatic circuit breaker, you can use a differential circuit breaker. These are two devices in one case. immediately monitors leakage current, short circuit, and overload. It is installed if there is a need to save space in the panel. If there is no such need, they prefer to install separate devices. It is easier to determine damage, cheaper to replace if it fails.

Operating principle of RCD

The protective shutdown device consists of a transformer, a relay and a disconnecting mechanism. The main working element of the RCD is a differential transformer with two primary windings and one secondary. It is he who compares the currents. The primary windings of a differential transformer have exactly the same parameters, but are connected towards each other. The current that goes to the load passes through one winding, and the current that returns from the load passes through the second winding.

When the line is in good condition, the currents flowing through both primary windings are equal, but have opposite signs. As a result, the electromagnetic fields they create cancel out. In such a situation, there are no induced currents in the secondary winding, the contacts are closed, and there is power.

As soon as a leak appears on the monitored lines, an overweight appears in one of the primary windings (in the figure this is winding number 2). This leads to potential appearing on the secondary winding. When it reaches a threshold value (trip current), the relay is activated, cutting off the power. This is the principle of operation of an RCD.

In general, an RCD is a simple device, but very useful, since it is responsible for safety. For your safety and the safety of your children, we strongly recommend installing a residual current device in the switchboard.

Briefly about the parameters of the RCD

Despite the not too complicated device, there are many parameters by which it is necessary to select an RCD. This:

All these parameters are selected when drawing up the circuit, since the cross-section of the wire, the connected load and many other details are important for selection. So first you need to decide on the number and power of consumers (light bulbs, large and small household appliances, heaters, etc.).

What is a fire protection RCD

Clever minds have figured out how to use the operating principle of RCDs not only to protect people from electric shock when the insulation is damaged. The same device can be used to prevent fires. Structurally, they are no different, they are simply designed for high leakage currents.

How does the RCD work in this case? As you know, when current flows, the temperature of the conductors increases. If the current is sufficient, the heat can be so great that it can cause a fire. If you install a device with a leakage current of 100 mA or higher at the entrance to the house, it will not save a person from electric shock, but it can even prevent the occurrence of a fire. How? It may well happen that one of the protection devices turns out to be faulty. The phase insulation will be damaged, which will sooner or later lead to a fire. It may happen that the damage occurs on the unprotected part of the lines. In this case, the fire protection RCD will turn off the power. This will mean that there is too much leakage and it is necessary to inspect the wiring: measure the insulation, check the heating, etc.

A fire protection device is installed after the meter. If we talk about the parameters, the minimum shutdown current is 100 mA. The type is better selective, but choose the exposure time yourself. Selectivity will save you from false positives. Below, after the fire protection RCD, protection is installed on the line, selecting the disconnecting leakage current depending on the type of load.

If you follow GOST, then the installation of protective devices on lighting lines located in rooms with normal operating conditions is not necessary. That is, “personal” RCDs and automatic machines do not need to be installed on the lines that lead to lighting.

Manufacturers

There is no official rating of RCD manufacturers, so you should rely on reviews from practicing electricians. As a rule, when assembling a “sophisticated” shield, experts recommend using products from three European companies:

ABB (Swedish-Swiss company);
Legrand (France);
Schneider Electric (France).

In the catalogs of the above manufacturers, alternative names for residual current protection devices will be more often found. RCD - residual current switch (RCB). Difavtomat is an automatic residual current switch (RCCB).

The Schneider Electric company has developed a line of Easy9 devices belonging to the middle price segment.

Differential switch EASY 9 (RCD) 2P 63A 30mA (article EZ9R34263). Easy9 devices belong to the middle price segment, but at the same time they are distinguished by the quality, reliability and ease of use characteristic of equipment in the upper price segment

Many electricians are not satisfied with the quality of products from companies such as IEK, TDM, DEKraft, EKF.

In our age of high technology, people are surrounded on all sides by a huge number of devices and devices that operate using electricity. And the greater their number, the higher the likelihood of electric shock to a person. To avoid this, the RCD was invented. What it is and what it is needed for, we will explain in detail in this article.

Purpose

Intended to protect a person from electric shock when touching the housing of electrical equipment (household electrical appliances), which became energized if the insulation was broken.

When the RCD trips

Let's continue the story about the RCD. What is it and how does it work? An electric current begins to flow through a person touching the energized body of an electrical device. When it reaches 30 mA, the RCD turns off. As a result, the voltage is automatically disconnected from the damaged equipment. In this case, the person does not feel anything, since painful sensations occur at much higher currents (from 50 mA). A current of 100 mA is fatal to humans.

What does an RCD consist of?

Includes current transformer, (relay and breaking lever system), self-test circuit. More advanced devices contain in their design a system that is electromagnetic and inversely dependent on the magnitude of the cutoff current (protection from and against overload).

Operating principle of RCD

What it is? How is this device powered? Now we will tell you about all this in as much detail as possible. The operation of the RCD is based on current (CT). The phase and working neutral conductors pass through the current transformer. With normally operating equipment (with intact insulation), the magnitudes of the currents flowing through them are equal in magnitude, but opposite in direction. As a result of this, they induce CTs in the winding, identical in size, but opposite in direction, which completely compensate each other (there is no voltage at the ends of the secondary winding of the CT). If the insulation of the equipment is broken, part of the phase conductor current flows to the ground through the grounding conductor (if the device body is grounded) or through a person who has touched this electrical device. As a result of this, the amount of current flowing through the neutral working conductor becomes less than that flowing through the phase conductor. This leads to the fact that the magnetic fluxes in the transformer winding become different in magnitude. As a result, voltage appears at the ends of the CT winding. Current begins to flow through the relay connected to them. When the difference in values reaches 30 mA, a relay is activated, activating a system of breaking levers. The equipment turns off.

Turning on the RCD

It is carried out only after identifying and eliminating the fault in the electrical equipment that led to the operation of the device by pressing the cocking levers.

Conclusion

In this article, we introduced you to RCD in some detail: what it is, how it works and what it is used for. We hope you find this information useful.

Protective shutdown is especially important when a large number of different electrical appliances are used in the house. In this article we will look at residual current devices that are recommended and used in the construction of private houses. A diagram of the residual current device will be shown. Let's look at the question of what and when to use - an RCD or a difavtomat (differential machine). In addition, we will find out the main differences between residual current circuit breakers.

Types of circuit breakers

An important step in the organization of electrical safety are protective electrical devices or, as they are more often called, automatic devices. Conventionally, they can be divided into three types:

automatic switches (AB);
differential shutdown devices (RCD);
differential circuit breakers (DAB).

Fig 1. Circuit breaker

Fig 2. Residual current device (RCD)

Figure 3. Differential circuit breaker (DAB)

Operating principle of residual current devices

Automatic switches (AB), see Fig. 1, are installed to protect electrical wiring from overcurrents, and electrical consumers from short circuits. Overcurrent leads to heating of the conductor, which leads to fire of the wiring and its failure.

Residual current device (RCD) operating principle(Fig. 2). We install it to protect against electric shock in the event of breakdown of the insulation of equipment and wiring. The RCD will protect us even if we touch open, uninsulated sections of wiring or equipment that are energized at 220 V and will prevent a fire from starting if the wiring is faulty.

If a current difference appears, the RCD turns off the voltage supply. It is necessary to select an RCD based on two parameters: sensitivity and rated current. Typically, for home purposes, an RCD with a sensitivity of 300 mA is chosen. The rated current is selected depending on the total power of electrical consumers and must be equal to or be an order of magnitude lower than the rated current of the input circuit breaker (AB), because the RCD does not protect against short circuits and overcurrents. A residual current device (RCD) is usually installed in the circuit after the meter to protect all wiring in the house, see fig. 4, 5. According to modern standards, the installation of an RCD is mandatory.

Rice. 4. RCD connection diagram

Rice. 5 Electrical installation diagram for a house using an RCD

1 - sch distribution stream; 2 - neutral; 3 - w grounding ina; 4 - f aza; 5 - RCD; 6 - aw tomatic switch; 7 - pconsumer nutrition.

Differential circuit breakers (DAB) combine the functions of RCD and AV. The differential circuit breaker circuit is based on protecting circuits from short circuits and overloads, as well as protecting people from electric shock when touching live parts, see Fig. 6.

Rice. 6. Scheme of operation of DAV

These devices are widely used in household electrical networks (220/380 V) and in socket networks. A differential circuit breaker consists of a high-speed circuit breaker and a residual current device that responds to the difference in currents in the forward and reverse directions.

The operating principle of a differential machine. If the insulation of the electrical wiring is not damaged and there is no human contact with live parts, then there is no leakage current in the network. This means that the currents in the forward and reverse (phase-zero) load conductors are equal. These currents induce equal but counter-directed magnetic fluxes in the magnetic core of the DAV current transformer. As a result, the current in the secondary winding is zero and does not trigger the sensitive element - the magnetoelectric latch.

When a leak occurs, for example: when a person touches a phase conductor, the balance of currents and magnetic fluxes is disrupted, an unbalance current appears in the secondary winding, which triggers the magnetoelectric latch, which in turn acts on the release mechanism of the machine with the contact system.

To carry out periodic monitoring of the performance of RCDs and DAVs, a testing circuit is provided. When you press the "Test" button, a tripping differential current is artificially created. The activation of the protection devices means that it is generally in good working order.

Selecting a circuit breaker

Now, let’s decide in which case and which circuit breaker we should give preference to:

To protect the wiring of the lighting network, from which all our lamps are powered, we select automatic circuit breakers (AB) with operating currents 16 A.
The socket network in the house, which is used to turn on irons, table lamps, TV, computer, etc., must be protected by circuit breakers with differential protection (DAB).
For the socket network, we choose a DAV with an operating current of 25 A and differential current shutdown 30 mA.
To connect an air conditioner, dishwasher, electric oven, microwave oven and other powerful appliances that we need in everyday life, we need our own individual socket and, therefore, our own circuit breaker with differential protection. For example, to connect an electric furnace with a power of 6 kW, a differential circuit breaker with shutdown currents of 32 and 30 mA is required.

Paying attention, that all sockets must have a grounding contact. I recommend connecting power equipment, such as a grinding machine, to a circuit breaker. Since the entire network in our house is 220 V, we select the listed circuit breakers for the appropriate voltage.

Let's talk about the circuit breaker, which for safety reasons needs to be installed at the input. If we have protected all the outlet lines with automatic circuit breakers with differential protection, then at the input we install an automatic circuit breaker (AB) with a rated current determined by the technical conditions and a single-line diagram of the project “Electrical equipment of a residential building”.

But it is possible, after the input circuit breaker (AB), to install a residual current device (RCD) with a differential protection current of 300 mA. See Fig. 5 for such a connection diagram. If we choose this protection option, then it does not oblige us to install differential circuit breakers for the outlet network, but simply install an automatic circuit breaker (AB), see the same figure. 5. This scheme is acceptable if we have only one socket line with a number of sockets. But it is completely irrational if we have a number of independent receivers plugged into individual sockets.

For example: You have a current leak on the body of the washing machine and you accidentally touch it. The differential protection will instantly work and the DAV of the washing machine will turn off. It will not be difficult for you to identify and eliminate the cause. Just imagine how much work you need to do to find the reason for the RCD tripping at the input.

I would like to say that in the modern market of circuit breakers and RCDs there is a very large selection of devices, both domestic and foreign. It should be taken into account that domestically produced products are characterized by large overall dimensions, the ability to regulate current, lower price, and the service life in domestic conditions is almost the same.

Table 1. Comparison of the cost of circuit breakers

Conclusion

So, in the article we discussed the issues of electrical safety. They became especially relevant when a huge number of electrical appliances, consumer electronics and computers entered our home. The wiring carries a very high load and a protective shutdown is necessary. Modern technology is very expensive and demanding on the quality of networks. Therefore, you should not skimp on protective measures, because the cost of an RCD is not commensurate with the cost of the equipment in your home, and even more so with the cost of human life.

Please note: Prices are valid for 2009.

For many, it is no longer news that a modern household electrical network must have RCD protection. For those who do not yet know anything about such protective elements, let us say that this is the basis of human security. The device also helps prevent fires caused by electrical wiring. Therefore, familiarization with this element of protection and automation will not be superfluous. Let's talk in detail about the device, what is it structurally made of and what is the principle of operation of the RCD?

How does leakage current occur?

Below we will look at why an RCD is needed, but first let’s figure out what current leakage is? The entire operation of the device is connected precisely with this concept.

In simple terms, current leakage is the flow of current from a phase conductor to the ground along a path that is undesirable and completely unintended for this purpose. This could be the housing of electrical equipment or a household appliance, metal fittings or water pipes, or damp plastered walls.

Current leakage occurs when insulation is damaged, which can occur for a number of reasons:

aging as a result of long service life;
mechanical damage;

thermal effects when electrical equipment operates in overload mode.

The danger of current leakage is that if the insulation of electrical wiring is broken, a potential will appear on the objects described above (device body, water pipe or plastered damp wall). If a person touches them, he will act as a conductor through which the current will flow into the ground. The magnitude of this current can be such that it will cause the most tragic consequences, even death.

The video demonstrates the operation of an RCD

How to determine if there is a current leak in your home? The first sign of this phenomenon will be a barely noticeable effect of electricity, that is, when you touch something, you seem to be slightly shocked. This dangerous phenomenon is most often observed in bathrooms. In order to guarantee your safety in your own apartment, it must be equipped with protective elements.

RCDs (residual current devices) or differential circuit breakers are used for this purpose.

What is the basis for the operation of an RCD?

The operating principle of the RCD is based on the measurement method. At the input and output, readings of currents flowing through the transformer are recorded.

If the input current reading is higher than the output, there is a current leak somewhere in the circuit and the protective device will trip. If these readings are the same, then the RCD does not operate.

Let us explain this principle in a little more detail for a two-wire and four-wire system. An RCD in a single-phase network does not trip when currents of the same magnitude flow through the phase and neutral conductors. For a three-phase network, the same readings of the current in the neutral wire and the sum of the currents passing through the phase conductors are required. In both network options, when there is a difference in current values, this indicates an insulation breakdown. This means that a current leak will pass through this place, and the residual current device will trip.

After this, the RCD cannot be turned on until the location of the damage is detected.

Let's translate this whole theoretical principle of RCD operation into a practical example. A two-pole residual current device was installed in the home switchboard. An input two-core cable (phase and neutral) is connected to its upper terminals. A zero and a phase are connected to the lower terminals, going to some load, for example, to an outlet that supplies a water heating boiler.

Protective grounding of the boiler body is carried out with a wire that bypasses the RCD.

If the power supply is in normal mode, then the electrons move along the phase wire from the input cable to the heating element of the boiler through the RCD. They move back to the ground again through the RCD, but along the neutral wire.

The currents passing through the device have the same magnitude, but their direction is opposite (counter).

Let's assume a situation where the insulation on the heating element is damaged. Now the current through the water will partially end up on the boiler body, and then go into the ground through the protective grounding wire. The remainder of the current will return through the neutral wire through the RCD, only it will be less than the incoming current exactly by the current leakage reading. This difference is determined by the RCD, and if the number is higher than the response setting, the device immediately reacts to a circuit break.

The same principle of operation and operation of an RCD if a person touches a bare conductor or the body of a household appliance on which potential has appeared. Current leakage in such a situation occurs through the human body, the device instantly detects this and stops the supply of electricity by turning it off.

There will be no serious injuries because the RCD reacts almost instantly.

Design

The design of the RCD will help us understand how it reacts to current leakage. The main working units of the RCD are:

Differential current transformer.
The mechanism by which an electrical circuit breaks.
Electromagnetic relay.
Test node.

The transformer is connected to opposite windings - phase and zero. When the network is operating in normal mode, these conductors in the transformer core help induce magnetic fluxes that are in the opposite direction relative to each other. Due to the opposite direction, the magnetic flux in total is zero.

The device and principle of operation of the RCD is clearly shown in the following video:

An electromagnetic relay is connected to the secondary winding of the transformer; under normal operating conditions it is at rest. A current leak occurs, and the picture immediately changes. Now various current quantities begin to pass through the phase and neutral conductors. Accordingly, there will no longer be equal magnetic fluxes on the transformer core (they will be different both in magnitude and direction).

A current will appear in the secondary winding and, when its value reaches the set value, the electromagnetic relay will operate. Its connection is made in conjunction with a release mechanism; it will instantly react and break the circuit.

An ordinary resistance (some kind of load, the connection of which is made without passing through the transformer) serves as a test unit. Using this mechanism, current leakage is simulated and the operating condition of the device is checked. How does this check work?

There is a special “TEST” button on the RCD. Its main purpose is to supply current from the phase wire to the test resistance and then to the neutral conductor, bypassing the transformer. Due to the resistance, the current at the input and output will be different, and the created imbalance will trigger the shutdown mechanism. If the RCD does not turn off during the test, then you will have to abandon its installation.

Note! The RCD check must be carried out regularly, ideally once a month. This is a fire safety requirement and should not be neglected.

The internal design of different RCD manufacturers may differ, but the general operating principle remains unchanged.

All devices differ in the operating principle. They come in electronic and electromechanical types. Electronic RCDs have a complex circuitry and require additional power to operate. Electromechanical devices do not require external voltage.

How is the RCD indicated on the diagram?

For connected RCDs there are two generally accepted symbols on the diagrams.

Despite the design complexity, they tried to make the designation of the device as simple as possible. There is nothing superfluous, only the following elements:

A differential current transformer, which is schematically depicted as a flattened ring.
Poles (two for single-phase network, four for three-phase network).
A switch that acts to break contacts.

In this case, the poles have two types of designation:

Sometimes they are drawn in straight vertical lines depending on the number (two or four).
In other cases, for reasons of compactness, one vertical straight line is drawn, and the number of poles is applied to it in the form of small oblique lines.

Main operating characteristics of RCDs

In order for the device to work at the right time, it must be selected correctly according to its operating characteristics and connected.

The main parameter is the rated current value. This is the maximum current that this device can withstand over a long service life, remaining in working order and maintaining its protective characteristics. You will find this number on the front panel of the device; it must correspond to one of the readings in the standard series - 6, 10, 16, 25, 32, 40, 63, 80, 100 A. This RCD parameter depends on the load of the protected line and the cross-section of the conductors.

The RCD connection diagram provides for the joint installation of this device with circuit breakers.

This is important to remember, because the RCD only protects against current leaks, and the machine will react to disconnecting the circuit in short circuit and overload mode.

The video shows whether it is possible to connect an RCD if there is no grounding in the apartment:

In terms of rated current, the RCD must be selected an order of magnitude higher than the machine installed in pair with it.

The next important parameter is the rated residual current. This is the required leakage current value to turn off the RCD. There is also a standard series for differential currents, the values in which are normalized in milliamps - 6, 10, 30, 100, 300, 500 mA. But on an RCD this figure is indicated in amperes - respectively, 0.006, 0.01, 0.03, 0.1, 0.3, 0.5 A. You will also find this parameter on the device body.

To protect people at the RCD, it is necessary to set the leakage current setting to 30 mA, because values that are higher will lead to injury, electrical injury and even death. Since the environment in damp rooms is considered the most dangerous, a setting of 10 mA is selected on the RCDs protecting them.

We hope that by understanding the main purpose of the RCD and the principle of its operation, you will not neglect this important element of protection and make your life safe.