An ouzo residual current device is used for. The principle of operation of ouzo

The principle of operation of the RCD is based on measuring the current indicators that are recorded in the conductors during its passage through the transformer. If the current at the input and at the output are equal, the trip does not occur. And if the strength of the incoming current is higher than the outgoing current, there is a current leakage in the circuit and the RCD is triggered.

That is, the currents flowing through the phase and neutral wires must be equal (this applies to a single-phase two-wire network, for a three-phase four-wire network, the current in the neutral is equal to the sum of the currents that flow in the phases). If the currents are not equal, then there is a leak, to which the RCD reacts.

Devices are divided into several categories, depending on their intended purpose:

Electric shock protection - appropriate models are usually installed in rooms with a high level of humidity. In ordinary apartments, they can be found in the bathrooms. Most often, devices are installed on several circuits, divided into groups. They are not installed for each consumer group, due to the high cost of such a procedure. The principle of operation of the RCD is operational operation, under which it is easy to find out the cause of the failure and quickly establish it. All you need to do is to activate the switches in a certain order. In some cases, it makes sense to install the equipment separately, especially since the ouzo device allows you to do this.
Fire fighting devices - they are characterized by a specific cut-off. The equipment does not provide protection against electric shock. Its purpose is to protect against fire, which is provided under short circuit conditions. Often this happens due to overload or deformation of the wiring. The RCD deactivates the power supply of the entire house, building, which prevents a short circuit. Such models are installed in combination with counters.

Principle of operation

The principle of operation of the RCD and the connection diagram is determined by the features of the internal design of the equipment. It has several coils, one of which misses a phase, and the other is zero. Under the influence of current, fields are formed that, under normal conditions, cancel each other out.

If one of the elements registers a loss of balance, which often happens due to deformation of the conductor, the current goes to the ground. Immediately after this, the third element is activated, which promptly deactivates the power. It is important to determine whether the RCD works without grounding or not.

The device has several types of execution:

Two poles - models that are selected for networks with one phase
Four poles - suitable for a network with three phases.

What to choose depends on the design features of the network, some other factors, and the specifics of the schemes.

RCD test

The device must work properly. You can check this using several methods. First of all, we are talking about the "TEST" button. This is a special block, in fact, a contact. If this button is pressed, the device already connected is immediately deactivated. In the event that this, for some reason, did not happen, then it is better to refuse to use it.

What can be done with a faulty RCD:

Repair
Replace with a new, fully functional one.

Important! It is recommended to check the RCD regularly, ideally every month. This will help to control its serviceability, to track the appearance of various defects in time. In general, this is one of the conditions for fire safety, and it should not be neglected.

Connection Features

The principle of operation of the RCD in a single-phase network determines the features of its connection. It is important to note that such devices are intended for use in specific circuits:

TN-C-S.

A prerequisite is the correct connection to the wiring. Only in this case, under conditions of wiring deformation, the potential that is registered on the case will begin to flow to the ground through the conductor. The error will be fixed.

Important! Under the conditions of the standard supply mode, the device will not deactivate the load, and the household appliances will function normally. From the current that is in any of the phases, the flux F will be recorded in the wire. The values \u200b\u200bare the same, but the direction is different. Thus, they deactivate each other.

How does ouzo work in a leak condition? The potential, considered dangerous, goes to the ground, for which a special tire is responsible. In the design of the relay, the values caused by the imbalance are fixed. A high-quality and serviceable RCD will immediately identify existing malfunctions, moreover, the device instantly deactivates the circuit through contacts.

How does an ouzo with grounding work in a zero open circuit? It is important to note that under such conditions, static-type relays are disconnected from the power supply, respectively, their operation is suspended. In the case of a three-phase system, a distortion is recorded, as a result of which the voltage begins to increase significantly. If insulation deformation is registered in a weak area, the same will happen in the design of another case.

RCD in a two-wire circuit

Fulfilling its main purpose, ouzo has other important advantages. The device protects against damage equipment that is manufactured in accordance with TN-S. It is this factor that causes the growing popularity of such devices. Increasingly, they are being installed in two-wire circuits, which may or may not have PE conductors.

What happens in this case:

The body of the equipment is insulated, it does not come into contact with the ground in any way.
Under deformation conditions, the phase and its potential are recorded on the case, but it does not leave it
When in contact with equipment, a person is exposed to mortal danger - electric shock.

Important! In the framework of a circuit in which there are no RCDs, the current enters the body, but passes through it rather slowly. The device will detect the fact of a malfunction in time, quickly deactivate the voltage - this will happen in an instant. Thus, the risk of electric shock will be minimized.

Self-installation of RCD

Today, more and more often, the installation of RCDs is carried out by people who do not have sufficient knowledge and experience in the field of electrics. This can be dangerous, especially when it comes to old buildings prepared for renovation.

It is within the framework of the reconstruction, as a rule, that the transition to the use of TN-C-S is carried out. All that makes sense to do in this case is a ground loop. Another option is to connect the housing of household appliances to the water supply network, heating radiators, or to those elements of the building foundation that are made of metal.

Important! Connecting by yourself can lead to a dangerous situation if the wiring is faulty. This is fraught with damage. All actions related to the arrangement of the circuit should be performed at a high quality level. A prerequisite is the measurements necessary for control. This can only be done by specialists with sufficient experience.

RCD mount

Most of the devices on sale today:
stationary models. They are conveniently fixed to the ruler provided by the design of the shield.
portable models. They are connected to a standard outlet, and only in this position, the RCD feeds household appliances. The latter are somewhat more expensive, but the price is fully justified by their high quality characteristics, reliability and durability.

For RCDs, a PE ground bus is needed. Otherwise, when a potential appears on the body of the 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 danger 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. The 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 frame. 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.

In this article, we will talk about an electrical device called fully RCD - a residual current device. Residual current device (abbreviated as RCD) is a more complete name: a residual current device controlled by differential (residual) current or a mechanical switching device, which, when the differential (residual) current reaches (exceeds) the set value, should cause the contacts to open.

The main task of the RCD (Residual Current Device)

The main purpose of the RCD is to protect a person from electric shock and from the occurrence of a fire caused by current leakage through worn wire insulation and poor-quality connections.

Combined devices that combine an RCD and an overcurrent (short circuit) protection device are also widely used. Such devices are called UZO-D with built-in overcurrent (short circuit) protection, or simply a differential automat. Often differential automata are equipped with a special indication that allows you to determine for what reason the operation occurred (from overcurrent or from differential current).

Residual current device: purpose

RCD - a residual current device is installed in the electrical network of an apartment or house to perform the following electrical safety tasks:

Increasing the level of safety in the operation of household and similar electrical appliances by people;
Prevention of fires due to ignition of insulation of current-carrying parts of electrical appliances from differential (residual) current to the ground;
For diffusers. Automatic shutdown of a section of the electrical network (including residential) in case of overload (TK-current protection) and short-circuit current (MTZ-maximum current protection).

Note: In Russia, the use of RCDs became mandatory with the adoption of the 7th edition of the Rules for Electrical Installations ().

As a rule, one or more RCDs are installed on a DIN rail in an electrical panel.

(I talked about installing an electrical panel in an apartment in another blog article :)

SUMMING UP THE FIRST SUMMARY

There are two types of RCDs on sale - Residual Current Device:

RCD directly.
And UZO-D (differential) is an RCD + short-circuit protection device, in “one package”.

Important!

The use of an RCD is an additional protective measure, and not a replacement for overcurrent protection using fuses, since the RCD does not react in any way to faults if they are not accompanied by current leakage (for example, a short circuit between the phase and neutral conductors. Therefore RCD must be used together with Circuit Breakers (fuses)
RCDs can greatly improve the safety of electrical installations, but they cannot completely eliminate the risk of electric shock or fire. RCD does not respond to emergency situations, if they are not accompanied by leakage from the protected circuit. In particular, the RCD does not respond to short circuits between phases and neutral.
The RCD will also not work if the person is energized, but there is no leakage, for example, when a finger touches both the phase and neutral conductors at the same time. It is impossible to provide electrical protection against such touches, since it is impossible to distinguish the flow of current through the human body from the normal flow of current in the load. In such cases, only mechanical protective measures (insulation, non-conductive covers, etc.) and the shutdown of the electrical installation before servicing it are effective!

RCD characteristics

Now let's deal with the characteristics of the RCD indicated on the device case.

RCD - residual current device designed to protect a person from electric shock when indirectly touched (a person touches open conductive non-current-carrying parts of an electrical installation that is energized in the event of insulation damage), as well as with direct contact (a person touches current-carrying parts of an electrical installation that are under tension). This function is provided by RCDs of appropriate sensitivity (cut-off current is not more than 30 mA (milliamps).

Note: In the US, according to the National Electrical Code, ground fault circuit interrupters (GFCIs) designed to protect people must open the circuit at a current leakage of 4-6 mA (milliamps) (the exact value is selected by the manufacturer of the device and is usually 5 mA ) for a time not exceeding 25 ms (microseconds). In Europe, these values for RCDs, like ours, are 30-100 mA.

RCDs should operate in no more than 25-40 ms (milliseconds), that is, before the electric current passing through the human body causes heart fibrillation - the most common cause of death in electric shocks.

The list below shows the values of current through the human body and the most likely sensations that can be felt.

Important! don't try to experience it for yourself!

Current through the human body -0.5mA: not felt, weak sensations when touched with the tongue, fingertips and through the wound.
Current through the human body-3 mA: Feeling close to an ant sting.
Current through the human body-15mA: If you took hold of the conductor, it is impossible to let it go. Unpleasant, but safe.
Current through the human body - 40mA: Body spasms, diaphragm spasms. Danger of suffocation for several minutes.
Current through the human body-80 mA: Vibration of the ventricle of the heart. Very dangerous, leads to fairly quick death.

Hence the second short summary of the characteristics of the RCD

To protect a person in household electrical networks (single-phase current with a voltage of 220 volts), RCDs must be marked: cut-off current not more than 30mA, response time not more than 40 ms (milliseconds). Large manufacturers (such as ABB, Legrand) produce RCDs for human protection, with cut-off currents of 10 mA and 30 mA.

RCDs with a current of 30 mA are usually placed on group circuits. If you put an RCD of 10 mA, it is possible (there is always a background, natural leakage current in the apartment). 10 mA is usually placed on single consumers (washing machine, dishwasher). If you have a shower cabin, or a washing machine is installed in the bathroom (wet environment), using an RCD with a cut-off current of 10 mA is easy necessarily.

It should be repeated:

For damp and very damp rooms (saunas, baths, baths, showers), an RCD with a leakage current of 10 mA (milliamp) should be used.
For other premises, it is sufficient to use an RCD with a cut-off current of 30 mA (milliamps)
In wooden ladies, when conducting electrical wiring, in order to avoid fires, the installation of an RCD is desirable, or rather, it is simply necessary.

Note: On sale there are RCDs with cut-off currents and 100 mA and 300 mA or more. These RCDs (with 100 mA, 300 mA or more residual current breaking current are sometimes used to protect large sections of electrical networks (for example, in a private house or computer centers), where a low threshold would lead to false trips. Such low-sensitivity RCDs perform a fire-fighting function and do not are effective protection against electric shock.

RCD classification

Now let's note a few more points. In accordance with the classification, RCD - residual current device is divided into the following types:

Type AC-RCD, the opening of which is guaranteed if the differential sinusoidal current either suddenly appears or slowly increases.

Type A - RCD, the opening of which is guaranteed if a sinusoidal or pulsating residual current either suddenly appears or slowly increases.

The third result of the article

RCD type "A" is more expensive and more versatile, but both types "A" and "AC" are excellent for use in household electrical networks. Therefore, it is not worth focusing on this.

In wide sale, there are mainly RCDs of AC type (only the icon will be displayed on the facade of the device:

It should be noted that each RCD is designed to use a certain load in networks, namely a certain Amperage, which is indicated on the facade of the RCD. Since RCDs in electrical networks are used together with circuit breakers (fuses), I pay attention once again: the amperage of the RCD must be higher than that of the circuit breaker on the line.

RCD connection diagram

Now let's consider the RCD connection diagram - a residual current device, classical zeroing (TN-C). Most houses in the Russian Federation have a classic zeroing, in the apartments of these houses there is no separate dedicated ground line, that is, two, not three power wires run throughout the apartment.

Note: In accordance with GOST 50571_3-94 (Safety requirements. Protection against electric shock):

In the TN-C system, protection devices that respond to the RCD-D differential current should not be used;
When a residual current protective device RCD-D is used for automatic tripping in a TN-S system, the PEN conductor must not be used on the load side. The connection of the protective conductor to the PEN conductor (independent earth conductor) must be carried out on the power supply side, i.e. to a protection device that responds to differential current (UZO-D). The diagram shows the connection points of the RCD-D.

Before I connect the RCD, I pay attention to how the RCD circuit works. The principle of operation of the RCD is based on a comparison of the output (left into the apartment) and the input (returning from the apartment) current. If it turns out that the balance is disturbed, and less comes in than leaves, then the RCD turns off the power supply. If the RCD is installed for one line, then there are two options: put an automatic machine after the RCD or the device itself must have a built-in maximum current limiter. Connecting an RCD without a machine will cause a short circuit or constant overheating to disable it. I remind you: that the amperage of the RCD must be higher than that of the machine on the line. Note: In the figure, the phase wire is fed to the lower terminal of the introductory machine. This is not entirely correct, it is better to supply power to the upper terminal of the machine. Although I note that connecting the power wires from above is just a tradition. It is she, and not some technical reason, that determines the recommendation to connect from above. And, although from the point of view of safety, it would be better to connect everywhere the same way, there is no strict ban on connecting from below. However, it is highly desirable that within the shield, and even better - throughout the entire facility, power is supplied in the same way: either from above (everywhere) or from below (everywhere). Other connection schemes can be found in the article:.

Well, that's probably all I wanted to tell you about the RCD - the Protective Shutdown Device used in household electrical networks with a voltage of 220 volts. Good luck to you in your endeavors!

Specially for the site:

Dear guests, I am glad to welcome you on the pages of the Electrician's Notes website.

Today we will analyze with you an interesting article on the topic of the principle of operation of the RCD.

What is UZO? What is it for?

Residual current device (RCD) is designed for:

protection of people from the occurrence of a malfunction in the electrical installation
disconnection of voltage in case of accidental or erroneous contact with the current-carrying parts of the electrical installation during a current leakage
protection against ignition of electrical wiring in the event of a ground fault (housing)

Alternatives to RCDs have appeared on the electrical goods market - these are differential automata. Their peculiarity lies in the fact that they combine both the RCD and the circuit breaker.

Differential automata take up less space in, but they are several times more expensive. But we will talk about all the features of differential automata in the following articles. In order not to miss the interesting - subscribe to receive news.

The principle of operation of the RCD is based on the response of the current sensor to the changing input value of the differential current in the conductors.

The current sensor is the usual one, which is designed in the form of a toroidal core. The operating current setting is set on a magnetoelectric relay, which has a very high sensitivity.

RCDs made with a relay control body are very reliable and trouble-free.

But the development of electrical engineering does not stand still, therefore, not so long ago, electronic RCDs appeared, in which the controlling body is not a relay, but a special electronic circuit.

The relay acts on the actuator, which in turn opens the electrical circuit.

The executive mechanism consists of:

contact group (selected for maximum current - look at the RCD passport)
springs (to open the electrical circuit in case of abnormal operation)

To independently check the serviceability of the RCD, you must press the "Test" button. This creates an artificial current leakage, which is sufficient to trip the RCD. Thus, it is possible to independently perform RCD checks without the involvement of specialists. Checking the RCD with the "Test" button must be carried out monthly. For a more thorough check of the RCD, we produce.

And now we will consider the principle of operation of the RCD in more detail.

The operation of the RCD in the normal state of the network

In the normal state of the wiring (without leaks), the operating current (I1=I2) flows in anti-parallel and induces magnetic fluxes (Ф1=Ф2) of the same magnitude in the secondary winding of the current transformer, which compensate each other. At this moment, the relay does not work, because the current of the secondary winding of the current transformer is close to zero.

RCD operation in case of leakage

In case of accidental or erroneous contact with the current-carrying parts of the electrical installation, a leakage current appears. At this moment, the magnitude of the currents passing through the current transformer is violated (I1 is not equal to I2), therefore, a current (not balance) will appear in the secondary circuit of the current transformer, which will be enough to trigger the relay. The relay drives the spring mechanism and the RCD is turned off.

How the RCD looks like from the inside, see the figure below.

You can hear an opinion that disputes the need to install residual current devices (hereinafter referred to as RCDs). To refute or confirm it, it is necessary to understand the functional purpose of these devices, their principle of operation, design features and connection diagram. Also an important factor is the correct connection, depending on the specific task. We will try to answer as broadly as possible all questions regarding this topic.

Functional purpose

According to the official definition, this type of device plays the role of a high-speed protective switch that reacts to current leakage. That is, it works when a circuit is formed between the phase and the "ground" (PE conductor).

To give a classic example, an electric water heater is installed in the bathroom. It works without problems for a warranty period and even more, then there comes a moment when the body of one of the heating elements cracks and a phase breaks down into water.

If in this case a circuit is formed: phase - person - earth, the load current will not be enough to trigger the electromagnetic protection, it is designed for short circuit. As for thermal protection, its response time is much longer than the resistance of the human body to the destructive effects of electric current. The result can not be described, the worst thing is that in an apartment building such a boiler can pose a threat to neighbors.

In such cases, the presented device is the only effective way to provide reliable protection. It's time to consider its concept, design and principle of operation.

Device diagram

First of all, we present a schematic diagram of the device, indicating its main elements.

Designation:

A - Relay that controls the contact group.
B - Differential CT (current transformer).
C - Phase winding on DTT.
D - Zero winding on DTT.
E - Contact group.
F - Load resistance.
G - Button that starts testing the device.
1 – Phase input.
2 - Phase output.
N - Contacts of the neutral wire.

Now let's explain how it works.

Principle of operation

Let's say that a certain device with internal resistance R n is powered from our protective device, while the case of the connected device is grounded. In this case, during normal operation, currents equal in value, but different in direction, will flow through the windings I and II of the DTT.

Thus, the total value of i 0 and i 1 will be zero. Accordingly, the magnetic fluxes caused by the currents in the DCT will also be counter-current, therefore their total value will also be zero. Given the above conditions, no current will be generated in the secondary winding of the DDT, so the relay that controls the contact group is not initiated. That is, the safety device will remain on.

Now consider the situation in which a breakdown occurred on the body of the connected equipment.

As a result of the appearance of a leakage current (i y) to the "ground", the balance of currents flowing through the primary windings I and II will be disturbed. This will lead to the fact that the value of the magnetic flux will also become different from zero, which will cause the formation of a current (i 2) on the secondary winding of the TTT (III), to which the relay that controls the contact group is connected. It will work and the connected equipment will be de-energized.

The test button on the device simulates current leakage through the resistor R t, which makes it possible to verify that the device is working. This check must be carried out at least once a month.

Design

The figure below shows a typical protective device with the top cover removed, which allows you to see the main components of the design.

Designations:

A - The mechanism of the button that starts testing the device.
B - Contact pads for connecting the phase input and neutral wire.
C - Differential CT.
D - The electronic board of the current amplifier coming from the secondary winding, to the level necessary to operate the relay.
E - The lower part of the plastic housing with a standard DIN-rail mount.
F - Arc chutes on a breaking group of contacts.
G - Contact pads for connecting the phase output and neutral wire.
H - Release mechanism (operated by relay or manually).

List of main characteristics

Having dealt with the design of the devices and their principle of operation, let's move on to the main parameters. These include:

The type of electrical wiring to be protected, it can be single-phase or three-phase. This parameter affects the number of poles (2 or 4).
The value of the rated voltage, for two-pole devices is 220-240 Volts, for four-pole devices - 380-400 Volts.
The value of the rated current load, this parameter corresponds to that of circuit breakers (hereinafter AB), but has a slightly different purpose (will be described in detail below), measured in Amperes.
Rated differential (breaking) current, typical values: 10, 30, 100 and 300 mA.
Type of breaking current, accepted designations:

AC - Corresponds to sinusoidal alternating current. Both its slow increase and sudden manifestation are allowed.
A - In addition to the previous characteristics (AC), the ability to monitor the leakage of the rectified pulsating current is added.
S - Designation of selective devices, they are distinguished by a relatively high response delay.
G - Similar to the previous type (S), but with less delay.

Now it is necessary to explain the meaning of the rated current parameter, since some questions arise with it. This value indicates the maximum allowable current for this protective electromechanical device.

When choosing this parameter, it is necessary to take into account that it must be one step higher than that of the AB on this line. For example, if the AB is designed for 25 A, then it is necessary to install protective devices with a rated current of 32 A.

Please note that this type of device is not designed to operate from short circuit and overload. If such an accident occurs, then all the wiring will burn out and a fire will occur, but the device will remain on. That is why such protective devices must be used in conjunction with AB. Alternatively, you can install a diffuser, in fact it is also a residual current device, but equipped with a short circuit and overload protection mechanism.

Marking

The marking is applied to the front panel of the device, we will tell you what it means using the example of a two-pole device.

Designations:

A - Abbreviation or logo of the manufacturer.
B is the designation of the series.
C - The value of the rated voltage.
D - Rated current parameter.
E - The value of the breaking current.
F - Graphic designation of the type of breaking current, can be duplicated by letters (in our case, a sinusoid is shown, which indicates the type of AC).
G - Graphic designation of the device on circuit diagrams.
H - The value of the conditional short circuit current.
I - Device diagram.
J - The minimum value of the operating temperature (in our case: - 25 ° C).

We have given a typical marking, which is used in most devices of this class.

Connection options

Before moving on to typical connection diagrams, it is necessary to talk about a few general rules:

Devices of this type must be paired with AB, as we mentioned above, this is due to the fact that protective devices are not equipped with short circuit protection.
The value of the rated current of the protective device, it must be one step higher than that of the AB standing with it in a pair.
Do not confuse input and output contacts. That is, the input marked, as a rule, “1” should be supplied with a phase, and “N” should be zero. Accordingly, "2" is the phase output, and "N" is zero.
Zero after the apparatus must not be connected to zero before it.

Now let's consider the simplest circuit in which protection against short circuit and leakage current is installed on each line.

In this case, everything is simple, an AB is installed at the input (A in Fig. 7) with a rated current of 40 A. After it there is a common device (B), it is also called a fire-fighting device. This device must have a leakage current of at least 100 mA, a rated current of at least 50 A (see paragraph 2 of the general rules above). Next are two bundles of RCD-AB (C-E and D-F). The rated current parameter for "C" and "D" is 16 A. For "E" and "F" this parameter should be a step higher, in our case it is 20 A. As for the magnitude of the breaking current, for wet rooms this the indicator should be 10 mA, for other consumer groups - 30 mA.

This connection option is the simplest and most reliable, but at the same time more expensive. It can still be used for two internal lines, but when their number is 4 or more, it makes sense to install one protection device per group AB. An example of such a scheme is shown below.

As you can see in this scheme, we have one common (fire) protective device and four group ones for lighting, kitchen, sockets and bathroom. This connection option allows you to significantly reduce costs, compared with the scheme, where a bunch of RCD-AV is connected to each line. In addition, the necessary level of protection is provided.

In conclusion, a few words about the need for protective grounding. For the normal functioning of the RCD, it is necessary. On the Internet, you can find a switching circuit without PE (in fact, it is no different from the usual one), but it should be noted that the operation will only occur when there is contact with batteries, cold or hot water pipes, etc.