Protective shutdown ouzo. The principle of operation of the ouzo and the connection diagram in a single-phase network. Video: RCD connection

Probably, today there is no such owner of an apartment or house who would not have heard about RCD protective shutdown devices - what is it? This is the first question that is asked immediately when talking about this device. That is, everyone has heard that this is a protective device, but not everyone knows how it works, on what basis, what functions are assigned to it, what its main purpose is, but, more precisely, few people know. Therefore, there is a need in general terms, without going into the wilds of electronics and electricians, to deal with it.

What and from what protects RCD

Let's start with the fact that RCD has been used quite recently. Literally twenty years ago it was not used anywhere, therefore, even today it is not worth it in old houses. And most importantly, none of the owners of apartments and houses is going to install it. But in vain. Therefore, it is worthwhile to deal with the question of what an RCD is in electricians and what is its role in the safe operation of household appliances.

Many may say, why then install a circuit breaker, does the RCD repeat its functions? Doesn't repeat, that's for sure. Firstly, the circuit breaker installed in the switchboard is a protective device that opens the supply voltage network when an overload or short circuit occurs in it. That is, the machine protects the network itself. Secondly, the RCD is a device that protects people from the effects of current. How, that is, why do you need an RCD?

The thing is that any household appliances that we use daily, as well as electrical wiring, have a certain service life. After the latter, there is a high probability of failure of the insulation of electrically carrying sections. That is, the current begins to move not along a given circuit, but to the ground, if conditions are created for connecting the wiring to the ground. In this case, the conductor most often becomes the person himself.

For example, the standard situation is when any household appliance (vacuum cleaner, washing machine, electric kettle, and so on) breaks through the wiring, and the current begins to act on the device case (in fact, it is a bare live wire). If a person takes this device with one hand, and at the same time stands barefoot on a wet floor, then he will be shocked. And there are a lot of such examples where not only the floor, but also other parts of the building or communication systems can become a conductor. It turns out that in everyday life you can get an electric shock unexpectedly, without knowing where it came from. And for this it is not necessary to poke around in the outlet. That is why, in order to avoid such troubles, a residual current device is installed.

Of course, a ground loop, if it is provided in an apartment or house, as well as installed sockets with grounding, can save you from electric shock. But unfortunately, they are not installed everywhere, and grounding is not provided in all houses. So you can't do without RCD.

Attention! And one more thing, which concerns the strength of the leakage current. It is small, so the machines do not react to it.

That is, it turns out that the residual current device is triggered if it is the leakage current that appears. In the event that a person grabs two bare wires protruding from the outlet with both hands, then it will not work for sure. Because in this case, a person acts as a load, and circuit breakers should respond to this. Now, probably, the main application of the RCD becomes clear.

How many RCDs are needed

It is quite difficult to sort out the number of devices on your own. If you decide to use it in your own home, then invite a specialist for this. Offhand, we can say that if you are the owner of a one-room apartment, then one device is enough. If the apartment has four rooms (and this is fifteen groups of outlets, at least), then it is better to install five devices. Plus one more:

for all lighting
on a cooking electric stove;
water heater, if available.

Advice! All these devices will overload the home electrical network. Therefore, it is best to install differential automata instead of RCDs.

I would like to add that it is not always advisable to install a residual current device. For example, if old dilapidated wiring is still used in the house, then the RCD will most likely turn off the network for no reason, as it will constantly respond to dilapidated insulation, especially when the wires are under heavy load. In this case, it is recommended to use special sockets with small RCDs built into them. It is also better to install such sockets in places where there is an increased risk of leakage current.

Device marking

As for the marking, it is applied to the body of the device for the convenience of choosing it in terms of selection for operating conditions. The main characteristics of the RCD, which you need to pay attention to:

rated current with the unit of measurement ampere (A);
differential with a milliamp (mA) unit, this is the leakage current;
the type of the device itself.

For example, ratings can be indicated on the case: 50 A - in large print, below 300 mA - in small print. The type of device will also be indicated here in the form of a special icon. They are shown in the lower figure, where they are deciphered.

Please note that the electromechanical appearance of the device does not depend on the magnitude of the voltage. I mean its functionality. Electronic, on the contrary, is completely dependent on it. That is, the first one will definitely work even if there is no voltage in the network, the second one will never work without voltage.

Here on the case, usually on the side, the manufacturer must indicate the connection diagram of the device, which is a good hint for beginners who decide to install the protection and disconnection device with their own hands.

So, the marking makes it possible to make the right choice, exactly matching the requirements of the operating conditions of the RCD. Anyone who understands it and will calmly read and understand what the abbreviation of the device means, he will definitely select the device for the needs of the electrical network. Especially when it comes to site installation.

There is another frequently asked question that sounds like this - how can you distinguish an electromechanical RCD from an electronic one? In appearance, you can’t distinguish it in any way, so we advise you to consider the diagram printed on the case.

For an electromechanical in the diagram, a differential transformer (indicated by a cigar-like icon, that is, a rectangle with rounded ends) is connected directly to the polarization relay (it is indicated by a square).
An amplifier plateau is installed between the transformer and the relay (it is in the diagram in the form of a triangle). By the way, it is this plateau that requires the presence of voltage, it is this plateau that has to be fed.

There is another option, how to distinguish the two species from each other. To do this, you need a magnet, which needs to be moved around the RCD case a little: first along the front panel, then on the side. The main thing is that the device is turned on. If it works to turn off, then it is an electromechanical device, if not, then an electronic one.

Conclusion on the topic

So, in this article we tried to answer the questions of concern to our readers related to the residual current device, and in particular, what is it and why is an RCD needed? The ever-increasing invasion of household appliances has caused an increased occurrence of leakage current, which can cause electric shock to a person. And although the leakage current itself does not have great potential, and cannot kill a person, it is within his power to give him health-related troubles. So you should pay attention to this device and without fail to carry out its installation in your own house or apartment. As they say, safe and God saves.

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

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

1 Touching a person to non-current-carrying parts of the power plant that are energized due to insulation breakdown.
2 Touching a person to the current-carrying parts of the power plant, which are energized.
3 Occurrence of (differential) leakage current to the power plant housing or ground to prevent fire.

The principle of operation of the RCD. Scheme

Rice. 1

1 Differential current transformer
2 trigger element
3 Actuating mechanism
4 Button "Test" for monitoring the health of the RCD
I 1 – I 2 direction of current relative to load
I D - leakage current
F 1 - F 2 magnetic fluxes

Assignment of blocks.
1 Differential current transformer(used in most RCDs) measures the balance of currents between its constituent conductors.
2 trigger element(consists, as a rule, of electromagnetic relays) is used to control (influence) the actuator.
3 Actuating mechanism designed for emergency shutdown of the electrical circuit controlled by the RCD.
4 Button "Test" to control the health of the RCD by creating a simulation of the leakage current.

The principle of operation of the residual current device (RCD)

Circuit diagram

Rice. 2

1, 2 Primary windings
3 Secondary winding

When the controlled line is in good condition, there is no specified leakage current, and the transformer is in a state of rest (balance), because the currents in the oppositely connected primary windings of the transformer are equal. Due to the fact that equal magnetic fluxes going towards each other are mutually subtracted (that is, they are equal to zero), then an electromagnetic field does not arise in the secondary coil, which means that there is no voltage and no EMF that can act on the relay, on the basis of which the trigger mechanism is assembled (Fig. .1 ).

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

Attention!

It should be remembered that the RCD requires a monthly check, which is carried out by pressing the "Test" button. In this case, the electrical circuit is closed, emitting an artificial current leakage and the protective shutdown device is triggered. Lack of operation will indicate a complete malfunction of the device.

According to modern requirements, all electrical installations must have or. In this case, the resulting preset leakage 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 it is or that serves as the center of balance of the scales, 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 only responds 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 voltage overloads for which they are designed.

Visual electrical connection diagram of the RCD

Rice. 5

RCD. Video explanation

Choice of electromechanical RCD

I wish you successful installation remember electrical safety.

DIFFERENTIAL SWITCHES type VD1-63 (UZO). Manual

Passport

3421-033-18461115-2007 RE, PS

1 Purpose and scope

1.1 Circuit breakers, controlled by differential current, without built-in overcurrent protection, functionally independent of mains voltage for household and similar applications, type VD1-63 (RCD) 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 according to their characteristics they correspond to GOST R 51326.1 and technical specifications TU 3421-033-18461115-2002.

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

- protection of people from electric shock in case of indirect contact with accessible conductive parts of electrical installations in case of damage to the insulation (HP with a rated breaking differential current of 10; 30 and 100 mA);

- protection against fires arising from the ignition of the insulation of live parts of electrical appliances from differential (residual) current to the ground or due to a long flow of fault current in the event of failure of overcurrent protection devices (HP with a rated breaking differential current I D n = 300 mA);

- VD having a rated breaking differential current of not more than 30 mA can be used as a means of additional protection in case 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 Key features

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

Table 1

Characteristic name	Meaning
Number of poles	2	4
Rated AC operating voltage Ue, V	230	230, 400
Rated network frequency, Hz	50
Operational control device operating voltage range, V	from 115 to 265		from 200 to 460
Rated current In, A	16, 25, 32, 40, 50, 63, 80, 100
Rated residual breaking current I D n , mA	10, 30, 100, 300
Rated non-switching 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 than, A	3000
Operating characteristic in the presence of differential current with a DC component, type	AC
Electrical durability, on-off cycles (V-O), not less than	4000
Mechanical wear resistance of V-0 cycles, not less than	10 000
The maximum cross-section of the wire connected to the power clamps, mm 2	50
Presence of precious metals, silver, g	0.25 (per contact)
Climatic version and placement category according to GOST 15150	UHL14
Degree of protection according to GOST 14254	IP20
Service life, not less, years	15

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

table 2

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

2.3 Overall and installation dimensions are shown in Figure 1.

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

2.5 The use of HP 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 pc.;
packing box - 1 piece;
operation manual and passport - 1 copy.

4 Installation and operation

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

4.2 HP is installed on a mounting rail 35 mm wide (DIN-rail) in electrical panels with a degree of protection in accordance with GOST 14254 not lower than IP30.

4.3 After installation and verification of its correctness, supply voltage of the electrical network to the electrical installation and turn on the HP by moving the control handle to the “I” - “ON” position, press the button

"TEST". Immediate operation of the HP (disconnection of the circuit protected by the device) means that the HP is in good order.

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

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

this means that the electrical installation has a current leakage to earth caused by an unstable or short-term insulation failure. Check the operability of the HP by pressing the "TEST" button;

b) if the HP is not cocked,

then this means that in the electrical installation there is a defect in the insulation of any electrical receiver, electrical wiring, wiring 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, then this indicates the presence of an electrical receiver with damaged insulation. The malfunction is detected by connecting electrical receivers in series until the HP is triggered. A damaged electrical receiver must be disconnected. Check the operability of the HP by pressing the "TEST" button;

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

Checking is carried out by pressing the "TEST" button. Immediate operation of the HP and shutdown of the protected electrical installation mean that the HP is in good order.

Purpose

It is intended for a person from electric shock when touching the housing of electrical equipment (household electrical appliances), which, if the insulation is broken, turned out to be energized.

When RCD trips

Let's continue the story about RCD. What is it and how does it work? An electric current begins to flow through a person who touches the housing of an electrical appliance under voltage. When it reaches a value of 30 mA, the RCD turns off. As a result, the voltage is automatically disconnected from the damaged equipment. At the same time, a person does not feel anything, since painful sensations occur at much higher currents (from 50 mA). Lethal for humans is a current of 100 mA.

What does the RCD consist of?

Includes current transformer, (relay and break arm system), self-test circuit. More advanced devices contain in their design a system of electromagnetic and inversely dependent on the magnitude of the cut-off current (protection against and against overload).

The principle of operation of the RCD

What it is? How is this device powered? Now let's talk about all this in as much detail as possible. The RCD is based on current (CT). 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 reverse in direction. As a result, they induce CTs in the winding that are the same in magnitude but reverse in direction, which completely cancel each other out (there is no voltage at the ends of the CT secondary winding). If the insulation of the equipment is broken, part of the phase conductor current flows to the ground through the grounding conductor (if the instrument case is grounded) or through a person who has touched this electrical appliance. As a result of this, the amount of current flowing through the zero working conductor becomes less than the current 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. Through the relay connected to them, current begins to flow. When a difference of 30 mA is reached, a relay is activated, which activates a system of breaking levers. The equipment turns off.

Turning on the RCD

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

Conclusion

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

For RCDs, a PE ground bus is needed. Otherwise, when a potential appears on the body of an electrical appliance due to damaged insulation, there is no current leakage, and when you touch it and grounded metal parts (heating radiator, water pipes), you can get a noticeable electric shock. In this case, the protective device will work, but it will be better if this happens from leakage to the ground.

For reliable operation of the protective device, grounding must be laid. When working according to such a scheme, the RCD will break the circuit even before it touches the metal case of the equipment or household appliances.

RCD types

RCDs are classified according to their functions:

AC - response to a suddenly appearing or gradually increasing alternating leakage current.
A - additionally triggered by a constant pulsating differential current, which may appear unexpectedly or increase gradually.
B - response to direct and alternating pulsating leakage currents.
S - selective RCD with additional time delay for tripping.
G - similar to S, but with less delay.

Which RCD to choose?

Pulsating current in domestic conditions appears from washing machines, lighting dimmers, televisions, computers, power tools and other devices with switching power supplies. The absence of thyristor-controlled devices significantly increased the likelihood of leakage of direct or alternating pulsating current. Therefore, if earlier it was enough to establish the type of AC, now type A or B is needed.

Where to install RCD?

Public places in buildings where there is no increased risk of electric shock.
In electrical circuits with a possible risk of electric shock (rooms with above-normal humidity, socket groups, household appliances, etc.).
On the main input for protection against fire danger. Usually a selective RCD is installed here.
In storey in apartment shields, in individual houses.
In the radial ones, there is a common selective RCD and separate ones for the outlet lines, with a choice of parameters that guarantee selective operation.
At close stages of protection, for example, 10 and 30 mA, 30 and 40 mA, etc., the current selectivity of the RCD is unlikely due to the high response speed. For the indicated values, it is provided if you select a selective RCD of 100mA so that there is still a time delay.
Due to the aging of the insulation, there is not always a gradual increase in leakage currents.
With an instantaneous increase in leakage current due to insulation breakdown, any conventional RCD in series in the circuit can operate. This happens due to the rapid and significant excess of the settings at once on several stages of protection.

The need to use selective RCDs

RCD selective performs its function of fire protection, if you apply modifications with a time delay - S or G. They are subject to increased requirements for short circuit resistance, switching capacity, dynamic and thermal resistance, etc.

Usually, a selective fire protection RCD is installed at the main input for a high leakage current.

RCDs cannot be used in circuits that cannot be suddenly turned off, as this can lead to emergency situations (fire or burglar alarms, danger to personnel, etc.).

In addition to RCDs, current selectivity must have The first to operate are those located closer to the overload or short circuit area. In this case, they are triggered before the short-circuit current reaches the limit value. This is necessary to prevent overloading of series-connected sections, since the current passes through the contacts of their protective devices.

Types of selective RCDs

For a selective RCD, it is important to pause so that a general type device, located below in the circuit, has time to operate. In this case, the device with a time-delayed shutdown passes a leakage current through itself and does not work. The delay interval for models may vary. For products marked S, it is 0.15-0.5 s, for example, RCD 63a 100mA is selective, with the ability to adjust the delay. The choice will be the best if they are installed at the input of the apartment's power cable. Some foreign models have even higher time delays. They are designed to turn off the circuit in the event of a fire hazard. The longer the protection is turned off, the greater the likelihood of ignition of the insulation.

When marked G, the device operates within 0.06-0.08 s. The device is fast enough to respond to network problems. It should be installed below RCD type S selective. With two-stage protection, it can be installed at the main input, since the speed of the RCD connected below is still higher.

If there are several groups of loads in the network, a separate protective device is connected in front of each, and a selective fire protection RCD is connected to the input. Then, if one of the lines fails, only it will be de-energized, and the rest will remain connected. With a similar wiring diagram, it is easier to detect a malfunction. If a conventional RCD turns out to be faulty or does not respond to malfunctions in the circuit, then a selective RCD (300 mA or 100 mA) will work and turn off the entire network.

To ensure selectivity, the following instrument settings are required:

set the response time of the selective RCD, if it provides for such an opportunity;
set the required shutdown parameters depending on the magnitude of the leakage current.

The tripping characteristics of RCDs of selective action must be at least 3 times larger than the others. Only in this case the device will be guaranteed to work.

RCD parameters

Two RCD time parameters are defined by Russian standards:

breaking time - the interval from the appearance of the breaking leakage current ∆i to the moment the arc is extinguished;
time limit for a device of type S is the time interval between the onset of ∆i and the opening of the contacts.

The last parameter determines the selectivity of the RCD. Its limit value is 0.5 s. In this case, it should be taken into account that for the protection of people, opening should occur within 10-30 ms, to prevent ignition of the insulation - up to 500 ms. RCD type S selective is widely used where it is necessary to exclude false alarms from the influence of interference or power surges.

RCDs are divided according to the network shutdown speed as follows:

general use - without delay;
type G - 10-40 ms;
type S - 40-500 ms.

Leakage currents always take place in electrical circuits. In sum, they should not exceed 1/3 of the nominal ∆i of the device. It is believed that for 1 A of load there is 0.4 mA of consumer leakage current, and for 1 m of the length of the phase wire - 10 μA. The protective device is adjusted according to the total natural leakage current. If this is not done, frequent false positives may occur. In this case, it should be taken into account that a device with ∆i=100 mA will no longer protect a person from electric shock.

When designing electrical networks, you can not specify the type of RCD, until experts require it. But you need to justify your choice in advance. It is important that the rated current of the device is higher than the expected load current. In addition, the RCD is installed only in a common pair with a circuit breaker. You can install one differential machine instead of two devices. It will cost less, but you should choose the right parameters.

RCD protects in two-wire networks where there is no protective conductor. But it works only after touching a dangerous place.

Which fire protection RCD to choose?

Selective RCD 63A, 300mA is usually installed at the input as a fire protection.

Many use conventional generic models by installing 30 mA protection devices in the house. Here, the function of "partial" selectivity is fulfilled due to the large difference in operating currents. This saves money on the price difference. In addition, a conventional RCD provides better safety due to faster response when catching leakage currents. The difference in the behavior of the devices is that the selective device will not trip first at a differential current equal to or greater than 300 mA. Such a situation is already extraordinary and there is no question of whether to go to the control panel, which may be located on a street pole. With such a large current, an ordinary RCD will probably work if an accident occurs on the line. Here and so it will be clear where to look for a malfunction.

Thus, a fire RCD can be installed both selective and conventional.

RCD manufacturers

The Legrand Group is a world-renowned manufacturer of building electrical systems. The leading positions are ensured by the highest production culture and large investments in the creation of new electrical products. For Russia, the group supplies the entire range of electrical equipment, from sockets and switches to the most complex control systems.

Selective RCD Legrand is of electronic and electromechanical type (indicated on the front panel). Depending on the version, it is installed on the side or below the circuit breakers. Adjustable time delay (0-1.3 s) and sensitivity. In combination with automatic devices, they are used as highly sensitive or basic protective devices.

RCD prices remain high, like other brands.

By ABB, RCDs are most fully represented by the F 200 series - from 16 A to 125 A. RCD 63A, 100mA selective is sufficient for a home network. For leakage currents for household appliances, a 30 mA device is usually used. As a fire protection at the input of a private house, a selective RCD ABB (63A, 300mA) four-pole for a three-phase network is used, as one of the most reliable. It is not inferior in quality to Legrand brand products. For an apartment with a single-phase input, there will be a two-pole device. The photo below shows a selective RCD ABB 63A, 300mA.

The maximum current that the device can withstand is from 3 to 10 kA (indicated on the front panel). It is short-term, not working current. The RCD is able to pause until the machine disconnects the circuit.

The company is one of the leading, but the prices are very high. Consumers often prefer abb models because safety is the most important thing. ABB DDA200 AP-R type A and AC differential block is available. It has a trip delay of 10ms, although it is not an ABB selective RCD. Its tripping characteristic curve is located between selective and conventional RCDs. The device has an increased resistance to false alarms compared to general purpose devices.

The rejection rate for ABB selective RCD, as well as for other products, is only 2%, due to which there are practically no problems in operation. Electromechanical devices are much more reliable than electronic ones and have pluses in everything, except for the price. RCDs with an electronic actuator are already beginning to appear, not inferior in reliability to a mechanical one.

On the market you can find products half the price, and the quality is not inferior to ABB. The company also produces the FH 200 series, which has a slightly lower price, but significantly loses in quality to the F 200 products. In particular, it does not have such reliable conductor fastening contacts that quickly begin to dangle, which affects the quality of work.

If you purchase an ABB selective RCD, then only in specialized stores, and not in dubious places. A fake is dangerous because it is not able to protect a person properly. On modular equipment, the list of which also includes RCDs, samopalshchiki pay great attention because of the high cost.

The domestic group of companies IEK produces about 7 thousand items of products that meet international standards and ensure the reliable operation of power grids.

RCDs are subject to high requirements. On the one hand, they must work reliably, protecting people from and wiring from the risk of ignition. But at the same time, devices installed at different stages of electrical circuits must act selectively, turning off individual sections. These conditions, as well as GOST 51326.1, correspond to the selective RCD IEK type VD1 63S.

The product group is represented by rated currents of 25-80 A, and differential currents are 100 mA and 300 mA. Products are cheaper than those of famous brands and are widely used as introductory fire fighting apparatus. In this case, the protection selectivity is ensured by high cutoff currents and time delays for circuit disconnection.

Choice of protective devices

If electricity is consumed in a simple way, a sinusoidal current flows through the circuit. The leak will be of a similar shape and AC type devices can be used here.

In modern household appliances, phase-cut control circuits are increasingly used. An AC type device will not respond to them, and here it is better to use an RCD of type A, which also responds to a sinusoidal current. Devices can be used together, for example, type AC is suitable for lighting with incandescent lamps, and type A is suitable for sockets to which devices with pulse regulation can be connected. But if you have to change the lighting to energy-saving lamps with brightness control by phase cut-off, you will also have to replace the device type AC with A. Otherwise, it will not work.

In order to separate the operation by the levels of electrical circuits, it is necessary to use selective devices. Type S is installed at the main input, type G is installed at the second level, and then instantaneous devices.

The RCD is selected one step higher in rated current than the circuit breaker connected in tandem with it, which can operate for a long time when the load is exceeded. If there is a 50 A machine at the input, a selective RCD 63A will suit it.

According to the requirements of the standards, the nominal values of the voltage, as well as continuous and interrupting current ∆i are indicated on the front panels of the devices. If there is a designation of a sinusoid, this is the AC type. The presence of two positive half-cycles under it means type A. Selective RCDs are denoted by the letters S and G. The rated short-circuit current is indicated in the box. The device must withstand its increase to the maximum until the machine turns off. Usually the current does not have time to reach the limit value. The RCD disconnects the circuit with a defect in advance, until the conductor has heated up and the insulation has not ignited.

Conclusion

In electrical household networks, current and time selectivity is used. To do this, protective devices are installed in series according to a tree diagram, where one switch is common. The basis of the principle of operation is to reduce the time of current flow through the body with direct or indirect contact with the elements of electrical installations that are energized. RCD selective is installed at the entrance and performs a fire-fighting function.

The abbreviation RCD was created from the phrase "residual current device", which defines the purpose of the device, which consists in removing voltage from the circuit connected to it in the event of accidental insulation breakdowns and the formation of leakage currents through them.

Principle of operation

For the operation of the RCD, the principle of comparing the currents entering the controlled part of the circuit and the currents leaving it on the basis of a differential transformer is used, which translates the primary values of each vector into secondary ones strictly proportional in angle and direction for geometric addition.

The comparison method can be represented by ordinary scales or a balancer.

When the balance is maintained, then everything works normally, and when it is disturbed, the qualitative state of the entire system changes.

For a single-phase circuit, the phase current vector approaching the measuring body is compared and the phase current vector leaving it is zero. In normal operation with reliable whole insulation, they are equal, balance each other. When a fault occurs in the circuit and a leakage current appears, the balance between the considered vectors is violated by its value, which is measured by one of the transformer windings and transmitted to the logic block.

The comparison of currents in a three-phase circuit is carried out according to the same principle, only the currents of all three phases are passed through the differential transformer, and the unbalance is created on the basis of their comparison. In normal operation, the currents of the three phases are geometrically balanced, and if the insulation of any phase is broken, a leakage current occurs in it. Its value is determined by summing the vectors in the transformer.

Structural scheme

Simplified, the operation of the residual current device can be presented in blocks by a block diagram.

The unbalance of currents from the measuring body is sent to the logical part, which operates on the principle of a relay:

1. electromechanical;

2. or electronic.

It is important to understand the difference between them. Electronic systems are now rapidly developing and are becoming increasingly popular for many reasons. They have wide functionality, great capabilities, but require electrical power for the operation of the logic and the executive body, which is provided by a special unit connected to the main circuit. If the electricity goes out for various reasons, then such an RCD, as a rule, will not work. The exception is rare electronic models equipped with this function.

Electromechanical relays use the mechanical energy of a cocked spring, which resembles an ordinary mousetrap by the principle of operation. In order for the relay to work, a minimum mechanical force on the sensed actuating element is sufficient.

Just as a mouse touches the bait of a prepared mousetrap, the leakage current that occurs during an unbalance in a differential transformer leads to actuation of the actuator and disconnection of voltage from the circuit. To do this, the relay has built-in power contacts in each phase and a tester preparation contact.

Each type of relay has certain advantages and disadvantages. Electromechanical designs have been operating reliably for many decades and have proven themselves well. They do not require external power, and electronic models are completely dependent on it.

It is now generally accepted that the most effective measure of protection against electric shock in electrical installations with voltages up to 1000 V is a residual current device (RCD) for leakage current.

Without objecting to the importance of this protection measure, most experts have been arguing for many years about the values of the main RCD parameters - installation current, tripping time and reliability.This is explained by the fact that the parameters of the RCD are closely related to its cost and operating conditions.

Indeed, the lower the setting current and the shorter the response time, the higher the reliability of the RCD, the more expensive its cost.

In addition, the lower the setting current and the shorter the RCD response time, the more stringent the requirements for the insulation of the protected area, since even a slight deterioration in it under operating conditions can lead to frequent, and in some cases long-term, false shutdowns of the electrical installation, thereby making it impossible normal operation.

On the other hand, the higher the RCD setting current and the longer its operation time, the worse its protective properties.

RCD design

The layout of a single-phase RCD is shown in the picture below.

In it, voltage is applied to the input terminals, and a controlled circuit is connected to the output terminals.

A three-phase residual current device is made in the same way, but the currents of all phases are controlled in it.

The figure shown shows a four-wire RCD, although three-wire designs are commercially available.

How to check RCD

Every design model has a built-in functionality check function. For this, the "Tester" block is used, which is an open contact - a button with a spring self-return and a current-limiting resistor R. Its value is selected to create the minimum sufficient current, artificially simulating leakage.

When the "Test" button is pressed, the RCD connected to the operation should turn off. If this does not happen, then it should be rejected, look for a breakdown and repair or replace it with a serviceable one. Monthly testing of the residual current device increases the reliability of its operation.

By the way, the serviceability of electromechanical and individual electronic structures is easy to check in the store before purchase. For this purpose, it is sufficient, when the relay is on, to briefly apply current to the phase or zero circuit from the battery with any connection polarity according to option 1 and 2.

A working RCD with an electromechanical relay will work, and electronic products in the vast majority of cases cannot be checked this way. They need power for their logic to work.

How to connect an RCD to a load

Residual current devices are designed for use in power supply circuits according to the TN-S or TN-C-S system with the connection of a protective neutral PE bus in the wiring, to which the cases of all electrical devices are connected.

In this situation, if the insulation is broken, the potential arising on the case immediately flows through the PE conductor to the ground and the comparison body calculates the fault.

In normal power supply mode, the RCD does not disconnect the load, so all electrical appliances work optimally. From the current of each phase in the magnetic circuit of the transformer, its own magnetic flux F is induced. Since they are equal in magnitude, but oppositely directed, they cancel each other out. The total magnetic flux is absent and cannot induce an EMF in the winding of the relay.

In the event of a leakage, dangerous potential flows to earth via the protective PE busbar. EMF is induced in the relay winding from the resulting unbalance of magnetic fluxes (currents in phase and zero).

The residual current device instantly calculates the fault in this way and in a fraction of a second de-energizes the circuit with power contacts.

Features of the RCD with an electromechanical relay

The use of the mechanical energy of a cocked spring in some cases can be more profitable than the use of a special block for the electrical supply of the logic circuit. Consider this using an example when the zero of the supply network is broken, and the phase is supplied.

In such a situation, the static electronic relays will not receive power and, therefore, will not be able to work. At the same time, in this situation, a three-phase system has a phase imbalance and an increase in voltage.

If an insulation breakdown occurs in a weakened place, then the potential will appear on the case and will leave through the PE conductor.

In an RCD with an electromechanical protection relay, they will work normally from the energy of a cocked spring.

How RCD works in a two-wire circuit

The undeniable advantages of leakage current protection in electrical equipment made according to the TN-S system through the use of RCDs have led to their popularity and the desire of individual apartment owners to install RCDs in a two-wire system not equipped with a PE conductor.

In this situation, the body of the electrical appliance is isolated from the ground, not in communication with it. If an insulation breakdown occurs, then the phase potential appears on the case, does not drain from it. A person who has contact with the ground and accidentally touches the device falls under the action of the leakage current in the same way as in a situation without an RCD.

However, in a circuit without a residual current device, the current can pass through the body for a long time. When the RCD is installed, it will sense a malfunction and turn off the voltage during the setting time within a fraction of a second, which will also reduce the degree of electrical injury.

Thus, the protection makes it easier to save a person when it gets under voltage in buildings equipped according to the TN-C scheme.

Many home craftsmen try to install RCDs on their own in old houses awaiting reconstruction to switch to the TN-C-S system. At the same time, at best, they perform a self-made ground loop or simply connect the housings of electrical appliances to the water supply network, radiators, and iron parts of the foundation.

Such connections can create critical situations in the event of a malfunction and cause serious damage. Work on the creation of a ground loop must be carried out with high quality and controlled by electrical measurements. Therefore, they are performed by trained professionals.

Mounting types

Most RCDs are made in a stationary version for mounting on a common Din-rail in an electrical panel. However, on sale you can find portable structures that are connected to a conventional electrical outlet, and the protected device is powered from them further. They cost a little more.