Electromechanical, electronic RCD: features

In recent decades, the range of protective electrical devices has been supplemented with residual current devices (RCDs), differential circuit breakers (DIFs), and surge protection devices (SPDs). The listed protection devices make it possible to increase the safety of operation of electrical networks. This material is dedicated to RCD. More precisely, one of the varieties of residual current devices - an electromechanical RCD.

On a note! RCDs are often called residual current devices (RCDs). This name is associated with the principle of operation of protective devices. The design and principle of operation of the UDT will be discussed below.

Purpose of RCD

Most current protection devices (fuses, circuit breakers, etc.) protect electrical wiring and electrical receivers connected to it from overload and short circuit currents. Residual current devices perform other functions. Depending on the triggering current, they protect people from electric shock or prevent fire.

Every electrician knows that industrial frequency alternating current flowing through the human body becomes hazardous to health if its value exceeds 0.01 ampere. Currents above 0.1 A are deadly. Therefore, the threshold operating current (setting) of the RCD protecting a person from electric shock is usually selected from the ratings of 10 mA or 30 mA. The first setting is used for damp rooms, children's rooms, and so on. The 30 mA setting applies to normal conditions.

To prevent fires, devices are installed that are configured for differential currents exceeding 300 mA.

RCD, differential circuit breaker and RCBO - what is the difference?

All these devices successfully perform the function of switching off in case of current leakage, and have the letter “D” in their name - differential. The difference is that differential automatic machines have additional built-in overcurrent protection. That is, they additionally protect against overload currents and short-circuit currents, having a thermal and electromagnetic release on board.

Three differential protection devices - HP, IM, RCBO

In terms of functions, everything is simple, but in real life it may not be possible to distinguish RCDs from differential automatic devices the first time. I'm telling you.

The main external signs of an RCD (differential switch, VD):

The RCD has the designation “VD” in its name - differential switch. True, only manufacturers who use Russian letters in their names have this.
RCDs do not have a protective characteristic letter in front of the rated current value (most often this is the letter “C”).
For RCDs, the letter “A” is written after the current value. Examples – 16A, 25A, 32A.
On the side wall of the RCD they sometimes write “Differential Switch (RCD)”.
The diagram indicated on the RCD body does not include designations of thermal and electromagnetic releases.

The main external features of differential automatic machines (IM and RCBO):

The model name on the body always contains the letter “A” (BP, RCBO).
The letter of the protective characteristic is always indicated (B, C, D).
After the rated current, the letter indicating amperes is not placed. Examples – C16, C25, C32.
On the side wall, as a rule, it is written that in front of us is a machine gun.
The diagram shows the thermal and electromagnetic release.

The differences in the HP, IM, RCBO circuits in terms of the presence of releases and overcurrent protection are visible below:

HP, IM, and RCBO - protection circuits are available only on the 2nd and 3rd circuits

differences between AD difavtomats and RCBOs , except perhaps in design. The IM has a series-connected circuit breaker and RCD in different housings, connected into a monolithic structure. AD is a more compact device.

The main external difference between differential protection devices and conventional circuit breakers is that in addition to the rated current In, the rated differential current IΔn (10, 30, 100, 300, 500 mA) is indicated on the HP, IM, RCBO.

By the way, PUE 7.1.76 directly states that it is recommended to use an RCD with an overcurrent protection device as a single device. This is necessary in order to guarantee the presence of protection and the correct protection current. After all, the consumer can install the machine at a higher current, or not install it at all. You never know.

In the second part of the article, we will consider the internal structure and differences of differential protection devices in more detail.

Operating principle of an electromechanical RCD

Residual current devices respond to leakage currents that occur when the insulation of electrical wiring is broken or when a person touches live parts that are energized. The main feature of leakage currents is that they upset the balance (equality) of currents flowing through the phase wires and the neutral wire.

A differential transformer is used to detect leakage. Structurally, it consists of:

a ferrite ring serving as a magnetic circuit (core);
primary windings, which are phase conductors and a neutral wire passed through the core;
secondary (measuring) winding.

In the absence of leakage currents, the total magnetic flux created in the transformer core by the primary windings is zero. In this case, there is no EMF in the secondary winding. If a leak occurs, the balance of currents is disrupted and an EMF begins to be induced in the secondary winding. A potential difference occurs at the terminals of the measuring winding. The higher the leakage current, the higher the potential difference.

On a note! Electrical protection based on comparison of currents is called differential current protection .

The voltage removed from the secondary winding of the differential measuring transformer is supplied to the threshold organ (comparison device). The threshold organ generates a shutdown signal when the leakage current reaches the set value.

A polarized relay is used as a threshold element in electromechanical disconnecting devices. In an electronic RCD, the comparison device is a DC amplifier made on an operational amplifier chip.

Is it necessary to install an RCD?

As the practice of operating modern electrical appliances shows, it is almost impossible to get an electric shock during their operation if basic safety rules are observed.

Typically, the most dangerous place in portable electrical appliances is the power cord. As a result of bending, especially at the exit point from the electrical appliance and the plug, it will fray over time and the insulation may be damaged. Therefore, before connecting an electrical appliance, it is imperative to check the integrity of the cord insulation.

Modern electrical wiring has an additional grounding wire, to which the metal housings of electrical appliances are connected via an electrical plug. Therefore, in the event of an insulation breakdown, the circuit breaker will trip.

In apartments of old construction, there is no grounding wire in the electrical wiring, but the insulation is already worn out and, as a result of leakage currents, the RCD may give false alarms and the RCD should not be installed.

In addition, the RCD is connected to the break of the phase and neutral wires, as a result, four additional connections appear, which reduces the reliability of the electrical wiring as a whole, since it is at the connection points that contact is most often broken.

Based on the foregoing, we can conclude that existing protective measures even without an RCD reliably protect a person from electric shock.

The only justified case, from my point of view, is the installation of an individual RCD on electrical appliances installed in rooms with electrically conductive floors with high humidity. Such rooms include, for example, a bathroom.

But I am sure that in the near future the rules of the PUE will oblige the installation of RCDs in household electrical wiring in new apartments and houses, and this is probably correct. If there is a chance to save the life of at least one person from electric shock, then you need to take it.

Electricians have one rule called the One Hand Rule. The essence of this rule is that when touching or holding an electrical appliance in one hand, it is unacceptable to touch grounded elements with the other hand - a water pipe or a central heating radiator.

Attention! Before any work with electrical wiring, to avoid electric shock, it is necessary to de-energize it. To do this, turn off the corresponding circuit breaker in the distribution panel and check the reliability of the shutdown using the phase indicator

Electromechanical UDT device

Electromechanical RCDs consist of the following main parts:

housings;
contact system consisting of terminals to which power wires are connected, moving and fixed contacts used for switching;
instrument transformer and rectifier;
polarized relay;
mechanical shutdown systems (release);
electric arc extinguishing systems;
test button and resistor.

Purpose of some elements

Polarized relay

The executive element in electromechanical differential current devices is a polarized relay. A polarized relay belongs to the class of bistable DC relays. It can be either in the off or on state in the absence of voltage on its winding. In the RCD, the winding of the polarized relay receives rectified voltage from the measuring transformer. When the threshold value is reached, the relay switches, which is mechanically connected to the release. As a result, the UDT is turned off.

TEST button

Unlike circuit breakers and other protective devices, RCDs have the ability to check the functionality of the device. The test is performed by pressing the “Test” button. This button, together with a specially selected resistor, forms a chain that simulates the occurrence of leakage current. The ends of the chain are connected to the neutral and phase wires. The string conductors do not pass through the ring core of the differential transformer. Therefore, during the test, the balance of magnetic fluxes in the measuring system is disrupted. The resistor value is chosen so that the artificial leakage current is equal to the rated operating current of the differential protection.

What is an RCD?

First, I’ll answer this basic question. “ RCD ” is an abbreviation that stands for “ Residual Current Device ”. RCD is also called this:

Differential switch (the abbreviation “VD” in the name and on the RCD body comes from these words),
Residual current switch (RCB),
Residual current device,
Differential protection switch,
Automatic circuit breaker controlled by differential current.

From the name it is clear that the main properties of this device are to distinguish (differentiate), turn off, and protect.

And if you want to find out official information on RCDs, refer to GOST R 51326.1-99 .

Update. From 01.03.21 GOST R 51326.1-99 is not valid. Instead, GOST IEC 61008-1-2020 . For electromechanical RCDs (independent of supply voltage), there is additionally GOST 31601.2.1-2012 , for electronic ones - GOST 31601.2.2-2012 .
For RCBOs, the new GOST number is GOST IEC 61009-1 –2020.

The difference between an electronic RCD and an electromechanical UDT

Electronic and electromechanical protection devices differ only in the type of threshold device. As noted above, electronic protection devices use an electronic amplifier as a threshold device, which generates a shutdown signal. This signal is sent to a conventional relay, which acts on a mechanical release. Electronic components, unlike electromechanical relays, are cheaper and have less technological variation. Therefore, an electronic RCD, as a rule, costs less than an electromechanical protection device.

People who have not previously encountered residual current devices often ask the question: how to distinguish an electromechanical RCD from an electronic one? Devices can be identified by markings on the front of the device. For all RCDs on the body you can see a symbolic image of a differential transformer. It is depicted as an ellipse enclosing power conductors. A symbolic communication line is drawn from the transformer going to the comparison device. The comparison device is depicted as a rectangle or triangle. If a triangle is drawn, then this is an electronic RCD. If the rectangle is an electromechanical device.

Important! If one or all of the images of the phase conductors connected to the moving contacts have bends in the form of an arc or a rectangular protrusion, then you are dealing with a circuit breaker. These bends represent the electromagnetic and thermal release respectively. If a measuring transformer and a comparison device are added to the “bends”, then this is a difavtomat.

On a note! All RCDs always have an even number of poles. Devices used in a single-phase network have two poles - phase and zero. Three-phase UDTs respectively have 4 poles. Zero terminals are always marked with the Latin letter “N”.

The eternal dispute about RCD

On electricians forums, debates continue on the topic: which protection device is better to use, electronic or electromechanical RCD?

In principle, there are no functional differences between devices with different threshold devices. Both types of differential current devices successfully perform their functions. But meticulous researchers have noticed one feature that the electronic RCD has. An op amp requires power to operate. It is taken from the input terminals of the protection device. Therefore, in the event of a break in the zero or phase supplying the electronic circuit, the device loses its functionality. An electromechanical RCD is free of this drawback, since the actuator is powered from the secondary winding of the transformer. Therefore, if the neutral wire breaks, the “electromechanics” will still work in the event of a phase leak.

Uzo electromechanical or electronic, how to distinguish and what is better to choose

Residual current switches (RCDs) are designed to cut off the voltage when a leakage current occurs, and modern or modernized wiring almost always contains this device in the electrical panel. But there are two types of RCD: electronic and electromechanical. In this article I will tell you how to distinguish them from each other and what is better to put in your home.

What is the difference between electronic and electromechanical RCDs

First, let's find out how they differ and on what principle they work. Let's start with the electromechanical one.

The main actuator of an electromechanical RCD is a differential transformer. Thus, in the event of a leakage, the current will pass through this transformer, and a current and voltage will also arise in the secondary winding of this transformer, which will cause the polarized relay, mechanically connected to the tripping mechanism, to operate. This will cause a shutdown.

And it turns out that regardless of whether there is voltage in the network at a given period of time or not, the electromechanical RCD will disconnect the damaged section of the network where the leakage current has arisen.

What about electronic?

And the electronic RCD will only work if there is a leakage current and the operating voltage is necessarily present in the network. Thus, if there is no power (the network is de-energized), then the electronic RCD will not work even if a leak occurs.

Here a completely logical statement arises: So what if it doesn’t work, there’s still no light!

This statement is not entirely true and now I will explain why.

Let's look at all possible emergency situations:

2. Break of the neutral wire. But this situation is much more dangerous and here’s why. Since there was a break in only one conductor, namely the working zero, the phase will still be present in the network. This means that electric shock is quite possible, and if at such a moment a breakdown of the washer’s insulation occurs, then when you touch it, you will be shocked, and the electronic RCD will be inactive, since there is no voltage, but only a dangerous potential.

3. The third very unpleasant moment is power surges. Because of them, electronic devices connected when a voltage surge occurs often fail. What is an electronic RCD? That's right, this device is constantly connected to the network. And a situation may well arise that the electronic board will fail and, because of this, the network will not be disconnected when a leakage current occurs.

It can be seen that the last two points in no way affect electromechanical RCDs, therefore, in my opinion, it is better to choose them for installation in your home.

So, we’ve decided on the type of RCD, now let’s learn how to distinguish them

How to distinguish electronic from electromechanical RCDs

The simplest and most accessible way to distinguish these products is to carefully examine the diagram that is drawn on all devices, because if you look closely at it you can find significant differences.

So, looking at the electromechanical RCD, you will see a differential transformer, it is connected through the secondary winding to a polarized relay, it also has a connection with the shutdown mechanism. As they say, mechanics in their purest form.

Now let's carefully study the circuit diagram of the electronic RCD

At first glance, the circuits are very similar, there is also a transformer and a relay, but in addition to these elements, this circuit contains one more, namely an electronic board to which power is supplied.

No power - no tripping of such an RCD.

We use a battery

Another option for determining which RCD is in front of you is to use any battery you have.

To do this, we take an RCD, a battery and two wires.

We clamp one ends of the wire to the RCD terminals

Then we turn on the RCD and touch the plus and minus ends of the battery. If nothing happens, then we swap the ends and lean against the battery again. Again, nothing happened - in front of you is an electronic RCD.

If the relay has worked (at least in one of the two options), then you have an electromechanical relay.

In these simple ways you can determine what type of relay is in front of you. And which one to choose, of course, is up to you, but I would install only an electromechanical RCD.

The article turned out to be useful and interesting, then thumbs up (like).

Thank you for your attention

How to choose the right RCD

We discussed the issue of using electronic and electromechanical devices above. They also talked about choosing a setting for different types of premises. There is one more parameter that should be taken into account when choosing a UDT. This parameter is the rated operating current. That is, the current that the RCD can withstand for an unlimited amount of time. When choosing a working “nominal value” you can follow a simple rule. The operating current must be no lower than the operating current of the machine, which protects the supply line from short circuit and overload.

What to consider when choosing an RCD

In order to choose an effective and safe device, you need to know some factors:

Understanding the purpose and principle of operation of the device you have chosen;
Know exactly its parameters and characteristics;
Study the regulatory documents supplied with the device.

An important role when choosing a machine is the age of your wiring, the condition and quality of the connections. Whether your apartment is new or old, whether there is a transformer substation nearby, the temperature conditions of the room where the electrical panel is installed - these are factors that influence the choice of a device that will protect you in any adverse situations.

A typical home electrical circuit diagram should look like this:

Input electrical panel;
Electrical panel on the lower floor;
Electrical panel on the second floor;
Each floor of the house has an electrical panel equipped with a group of automatic circuit breakers, individually for each apartment.

There are different types of RCDs, each of which performs specific tasks. Let's look at the indicators by which RCDs are classified.

Gradation:

type of current leakage;
response time;
shutdown principle;
number of poles.

Before making a purchase, you should determine exactly why you need the machine and what load it must withstand.

How to properly connect residual current devices

When connecting leakage current protection devices, several basic rules must be observed.

First and most important. RCDs and automatic devices must be operated in networks with a solidly grounded neutral with a separate grounding wire (three-wire or five-wire system). In this case, the housings of all electrical receivers protected by devices from leakage currents must be reliably grounded. Grounding can be carried out through the socket contacts or with a separate bolt-on wire.

Dangerous! Never use the neutral wire as grounding. Only a separate land!

Second. It is necessary to ensure that the wires are connected correctly. Zero should be connected to the terminals marked with the letter “N”, and phases to the phase terminals. This rule, which at first glance is not obvious, is associated with connecting the test button and the electronic protection circuit.

Third. Conductors of the same name protected by different RCDs cannot be connected to each other. This mistake is often made by inexperienced electricians when they use a common zero for several socket blocks. Such a connection, when connecting a load, immediately triggers the protection.

Example of RCD operation

Let's give a small example of a typical RCD-D. Given:

two-wire power supply circuit for 220 V, without grounding;
as an energy consumer - a washing machine;
switching device built into the circuit.

Normally, the RCD passes electricity directly and without obstacles. Incoming and outgoing currents are of equal importance. If, for example, an electric motor malfunctions, voltage will be applied to the body of the machine. By touching it, an unsuspecting person will be subjected to a powerful shock of electricity.

A leakage current and imbalance occurs: part of the energy flows through the body of the person under attack. Less electricity is returned to the RCD than was left, and the device breaks the circuit.

There are both simple mechanical protection devices and models with semiconductor contact breakers. There are also versions with more complex built-in logic. But electronic ones are more expensive and require additional power to maintain the operation of the circuits.

How to quickly check an RCD without connecting to the network

Each leakage current protection device has a test button. With its help, it is easy to carry out periodic checks of the UDT during operation. To test a large batch of disconnecting devices that are not connected to the network, you can use a regular 1.5 V AA battery.

If it is connected to the same poles (for example, to terminals 1-2), a working device will work instantly, since the current pulse during connection will not be balanced by the reverse current. RCDs with a rated differential current of 10 or 30 mA are triggered even by a dead battery.

Types of devices

Depending on the type of current flowing through your wires, there are two types of devices:

RCD type AC - protects against the effects of alternating current;
RCD type A is protection against alternating and pulsed current;
RCD type B – designed for use in industrial installations. It is triggered by leakage of alternating, direct and pulsating current.

At first glance, it seems that the issue is resolved, alternating current flows in all houses, therefore, we choose the AC type. However, modern household appliances, microwave ovens, washing machines, and most energy-saving lamps are equipped with a power supply that passes pulsed current through it.

Therefore, you can get an electric shock not only by trying to disassemble a faulty unit that is under voltage. Over time, any equipment wears out, which leads to damage to the secondary switching, which is why you can get an electric shock by touching the base of the household appliance.

An AC type RCD can operate on a pulse current, but with a long delay, and this can be dangerous to human life. European countries have long abandoned AC type machines; they are installed mainly on devices without electronics, such as underfloor heating or water heaters.

Often there are illiterate managers who do not know the difference between RCD type AC or A. It happens that they just want to get rid of stale goods. Unfortunately, the recommendations of electricians are also not always competent. AC protectors are a little expensive, but not more expensive than your life. The answer to the question of whether to choose an ouzo type A or AC is obvious.

Explanation of the principle of action of blood pressure

I’m writing for those who still haven’t clicked on the link above. AD consists of two parts or halves. The first one (on the left) is actually a two-pole circuit breaker with overcurrent protection. The second part (on the right) is an electronic RCD that does not have power contacts.

When the RCD is triggered, it does not open anything, but only makes it clear to the left side that it is time to turn off the load. Information is transmitted from the right side to the left through an electromagnet with a core, which, when triggered, extends and acts through a lever on the trigger mechanism of the machine.

To restart this system, a person needs two actions: turn on the machine, and press “Return” on the RCD.

General view of the electronic RCD board

Let's take a closer look at the electrical circuit of an electronic RCD. Here are all the electronics:

AD-67 Electronics, printed circuit board

I pulled out and laid out all the internal elements of the RCD:

All the insides of an electronic RCD

At the top right of the photo is an electromagnet with a core, which is the only actuator in the device in question.

RCD printed circuit board, view from the soldering side

What is the difference between an RCD and a machine in electrical engineering?

Domestic manufacturers produce products with sufficient characteristics. But they are inferior to foreign ones in response time, reliability of individual elements and quality of materials used. For an economically feasible power supply to a home with multi-level protection, you can combine electrical protection devices from different manufacturers. Input RCDs for 300 and 100 mA are domestically produced, and the load wiring is carried out through devices from ABB, Siemens, Schneider-Electric and similar devices with leakage currents of 10 and 30 mA.

Important: when the automatic circuit breaker is triggered, it is more difficult to determine the reason for the shutdown. Whether it is an overload or a leakage current, to find a fault it is necessary to completely remove the load and turn on the electrical appliances one by one. Some manufacturers provide devices with diffraction indicators, which makes it easier to find a breakdown.

For each power supply facility, a set of electrical protections is selected individually based on the condition of the wiring, type of network reconstruction, load and type of consumers (electrical appliances), and financial capabilities.

Rice. 2. Difference in the scheme indicated on the body

Nuances of operation

The pricing policy for both types of devices is ambiguous. The cost of an RCD is higher than a similar differential circuit breaker from the same manufacturer. This is due to ensuring the reliability and maintainability of the devices. If a combination of a circuit breaker and an RCD fails, as a rule, one product must be replaced. In the case of a differential switch, otherwise: a failed electrical protection cannot be repaired - a complete replacement of the unit is required. The practice of electricians shows that automatic machines break down more often due to low-quality electrical energy, lack of reconstruction of electrical distribution networks and electrical equipment at substations.

If the residual current device fails, it is possible to temporarily restore the power supply to the facility (apartment, while ensuring that the damaged section of the line is de-energized) by turning on the circuit breaker, which is located in the electrical circuit in front of it. If you install a difavtomat, you will need to install a working electrical product.

It is preferable to install differential switches in houses and apartments where power supply interruptions rarely occur. A residual current device paired with circuit breakers provides reliable protection with minimal financial investment.

Nuances of operation

Description

RCD ABB F202 AC - modular two-pole residual current switch. Designed for protection against indirect contact and additional protection against direct contact from alternating sinusoidal leakage current to ground, to disconnect power supply circuits with inductive and resistive loads.

The ABB F202 AC-16/0.01 residual current switch is used in residential, commercial and industrial premises.

The 2-pole RCD ABB F202 is equipped with a quick mounting system with which it can be easily mounted on a DIN rail in a distribution cabinet or box.

ABB F202 residual current devices comply with European standards IEC/EN 61008, UL 1053 a.

What is the difference between an RCD and a machine in electrical engineering?

Important: when the automatic circuit breaker is triggered, it is more difficult to determine the reason for the shutdown. Whether it is an overload or a leakage current, to find a fault it is necessary to completely remove the load and turn on the electrical appliances one by one. Some manufacturers provide devices with diffraction indicators, which makes it easier to find a breakdown.

Rice. 2. Difference in the scheme indicated on the body

How to avoid buying the “wrong” RCD?

In order to know how to distinguish VD1 63 differential or RCD visually, you need to pay attention to the diagram shown on the case. On electromechanical samples, the secondary winding of the differential relay is directly connected to the relay. There is no jumper to power the element from an external network.

Electronic RCDs are equipped with a circuit with an electronic amplifier board (in the form of a triangle).

To accurately check devices at home, you need a 1.5..9V battery (or battery), known to be charged. The RCD must be set to the “on” position. Connect two wires to the electrical device terminals, then to the battery poles. If there is no change, the polarity should be changed.

If the protective device is electromechanical, then when an electric current flows in the secondary circuit, a jump is detected, which triggers the relay and turns off the device. The lack of response to connecting the battery indicates that the RCD is electronic and does not work without external voltage.

An equally effective method is using a permanent magnet. If you hold the element near the front of the case, the switched on device will work if it is electromagnetic.

It is important for the consumer to decide what type of device is needed. Lack of load in the network can be for several reasons: failure of the external power supply network, repair work on the line. The cause may also be burnout of the neutral wire in the shield. In this case, the electronic type protective device does not respond to a malfunction: electrical appliances do not work, but the power to the phase wire does not disappear. It is in this case that the likelihood of emergency situations arises: if the insulation breaks down, for example, on a boiler, the phase gets into the housing. And when a person accidentally touches it, a leakage current begins to flow. In this case, the RCD will not work due to the lack of normal power supply.

How to avoid buying the “wrong” RCD?

Electronic RCDs are equipped with a circuit with an electronic amplifier board (in the form of a triangle).

An equally effective method is using a permanent magnet. If you hold the element near the front of the case, the switched on device will work if it is electromagnetic.

When observing frequent power surges in the network, the differential transformer is subject to rapid wear and failure. A burnt-out board with an amplifier is the cause of electric shock with all the ensuing tragic consequences. When purchasing an electronic type RCD, you should regularly test the sample. Weekly checks will help maintain the protective functions of the network.

Disadvantages and comments on the scheme

In similar circuits, I have seen the use of a transistor cascade in front of the thyristor. Perhaps in this circuit it was not required due to the high sensitivity of the thyristor or the design features of the differential transformer.

Despite the fact that the RCD (more precisely, IM) is declared to be of the “AS” type (operating from a sine wave), in fact this circuit only works on one half-wave. This can be seen even from the fact that the thyristor input circuit is shunted by a diode. It turns out that despite the fact that the response time of the RCD is stated to be 40 ms,

Maximum RCD response time

you need to add at least another half period (10 ms) to it. Or is this already taken into account in the tabular data?