RCD - device protective shutdown. Currently, RCD is used almost everywhere, and in new buildings it is mandatory.
We install RCDs in apartment panels and in electrical panels of private houses. And this, of course, is correct, only RCD saves a person from electric shock. Also, the RCD protects our apartment or private house from fires that occur due to faults in electrical wiring (poor contact, destruction of wire insulation). In my opinion, to such a question as how to install an RCD or not, there can only be one answer - The RCD must be installed in the electrical panel.
According to GOST 51326.1-99“Automatic circuit breakers controlled by differential current for household and similar purposes without built-in overcurrent protection” automatic circuit breakers controlled by differential current. current (RCD) have the abbreviation VDT(residual current switches). You can find this name for RCD in technical literature, in the names of products in online stores. In France, RCDs are designated ID (Schneider), in England - RCCD's.
Operating principle of RCD
Operating principle of RCD based on comparison of currents, which flow through the RCD, i.e. in your own words - what amount of current passed through the RCDto consumers, the same amount of current should exit back from the RCD through the neutral conductor. In the picture, I 1 is the current in the RCD to the power receiver, I 2 is the current in the RCD from the power receiver. I 1 = I 2 - this condition is met when the electrical wiring is done well or there is no interference in the operation of the electrical wiring.
Suppose a person touches some conductor (phase or zero), in this case the person “takes” part of the current I∆n onto himself, and there will no longer be equality between I 1 and I 2, because I 1 > I 2 - I∆n. The RCD will sense this and turn off, thereby saving a person from probable death due to electric shock. The RCD must operate within 25-40 ms so that the current that will flow through the body does not increase to a fatal level.
RCD by number of phases
RCD There are single-phase and three-phase. Here I think everything is clear, if the network is single-phase, then the RCD is single-phase - it occupies 2 modules (phase and zero). If the network is three-phase, then the RCD is three-phase - it occupies 4 modules (three phases and zero).
I would like to note that in private homes, where three phases with a power of 15 kW have recently been connected, it is not correct to protect people from injury electric shock or fire safety, install a common three-phase RCD, because if there is a current leak in one of the phases, a three-phase RCD will turn off all three phases. A three-phase RCD is installed on individual three-phase consumers, hobs (electric stoves), boilers in private homes.
Selection of RCD by rated current
Well-known manufacturers such as ABB and Schneider Electric produce modular RCDs, which are installed on a DIN rail, with rated currents of 16, 25, 40, 63 A. The rated current of the RCD shows the amount of current that the RCD can pass for as long as desired. Based on this range of rated currents, you should choose an RCD for an electrical panel in an apartment or private house.
It's important to know that The RCD does not have overcurrent protection(currents short circuit, overload) and therefore it should always be protected, the rated current of which is less than or equal to the rated current of the RCD - this is according to the rules. But I'm selecting an RCD in a different way strictly one step above the automatic .
I’ll explain why, the machine, as is known, passes current up to 1.13 of I nom. indefinitely long, and in the range from 1.13-1.45 I nom. for 1 hour. Suppose we chose a 25A machine and an RCD also 25A. As a result, for a whole hour, the RCD, which is designed for 25A, will pass a current of 25 * 1.45 = 36A, I don’t know what will happen to the RCD in this case, but I think that the 25A RCD is highly likely to burn out.
The rated current of the RCD is indicated on its front part.
There are RCDs with rated currents of both 32A and 50A, but these are Chinese RCDs, serious brands such as ABB, Schneider Electric or Legrand do not produce RCDs of this rating.
Examples of how to choose the right RCD based on rated current:
At the same time, remember that if “from above” the RCD is already protected by an automatic machine, the nominal value of which is less than the nominal value of the RCD, then after this RCD You can connect machines with a sum of ratings of at least 1000 A.
Rated breaking current of RCD
Rated breaking current of RCD I∆n(setpoint) is the current at which the RCD is triggered(turns off). The RCD settings are 10 mA, 30 mA, 100 mA, 300 mA, 500 mA. It should be noted that non-release current when a person can no longer unclench his hands and throw away the wire on his own, amounts to 30 mA and above. Therefore, to protect a person from electric shock, choose an RCD with a breaking current of 10 mA or 30 mA.
Rated breaking current of the RCD I∆n or leakage current is also indicated on the front panel of the RCD.
RCD 10 mA is used to protect electrical receivers in damp rooms or wet consumers, i.e. washing machines and dishwashers, sockets that are located inside the bath or toilet, light in the bathroom, heated floors in the bathroom or toilet, light or sockets on balconies and loggias.
SP31-110-2003 p.A.4.15 For plumbing cabins, bathtubs and showers, it is recommended to install an RCD with a rated differential trip current up to 10 mA, if a separate line is allocated for them, in other cases, for example, when using one line for a bathroom, kitchen and corridor, an RCD with a rated differential current of up to 30 mA should be used.
Those. The RCD with a setting of 10 mA is installed on a separate cable, to which only the washing machine is connected. But if from cable line other consumers are still powered, for example, sockets in the corridor, kitchen, then in this case an RCD is installed with a response current (set) of 30 mA.
ABB produces RCDs with a leakage current of 10 mA only at 16A. Schneider Electric and Hager have RCDs for 25/10 mA and 16/10 mA in their product line.
RCD 30 mA installed on standard lines, i.e. ordinary household sockets, lights in rooms, etc.
PUE clause 7.1.79. In group networks supplying plug sockets, an RCD with a rated operating current should be used no more than 30 mA. It is allowed to connect several group lines to one RCD through separate circuit breakers (fuses).
RCD 100, 300, 500 mA called fire protection, such RCDs will not save you from a fatal electric shock, but will protect your apartment or private house from a fire due to faulty electrical wiring. Such 100-500 mA RCDs are installed in input panels, i.e. at the beginning of the line.
In the USA they use RCDs with a rated breaking current of 6 mA, in Europe up to 30 mA.
It should be noted that The RCD is switched off within the setting range of 50-100%, i.e. if we have a 30 mA RCD, then it should turn off within 15-30 mA.
There are designers who promote double diffs. protection of “wet” consumers. This is when, for example, a washing machine is connected to a 16/10 mA RCD, which in turn is connected to a 40/30 mA group RCD.
In the end, what do we get? At the slightest “sneeze” from the washing machine, we turn off the entire group of machines (kitchen light, boiler and room light), because in most cases it is not known which RCD 25/30 mA or 16/10 mA will work, or whether both will work.
According to the set of rules for the design of electrical installations of residential and public buildings:
SP31-110-2003 p.A.4.2
But in fairness, it should be noted that if the electrical wiring is installed efficiently, then the RCDs do not operate for years. Therefore, in this case, the final word belongs to the customer.
Types of RCD according to the operating principle
Based on the operating principle, RCDs are divided into electronic and electromechanical. Electronic RCDs are an order of magnitude cheaper than electromechanical RCDs. This is explained by its lower reliability and low cost of production. An electronic RCD is “powered” from the network, and the operation of an electronic RCD depends on the parameters and quality of this same electrical network.
Let me give you an example: our zero in the floor panel has burned out, and accordingly the power to the electronic RCD will be lost and it will not work. And if at this time a phase short circuit occurs on the body of the device, and a person touches it, then the electronic RCD will not work, because it simply simply does not work, there is no power supply to the electronics due to a zero break. Or if, simply put, electronics are electronics, and Chinese electronics are doubly “electronics” that can fail at any moment. Therefore, an electromechanical RCD, which does not depend on the state of the network, is much more reliable than an electronic RCD.
The principle of operation is based on a comparison of the incoming and outgoing current of the RCD of a conventional differential current transformer, and if the current is not equal to and greater than the setting (rated breaking current of the RCD in mA), as already indicated above, then the RCD is turned off.
From these diagrams you can determine whether the RCD is electronic or electromechanical; the diagrams are applied to the RCD housings.
Well-known manufacturers such as ABB, Schneider Electric, Hager or Legrand do not produce electronic RCDs, only electromechanical RCDs. I install electromechanical RCDs in my electrical panels.
To compare electronic and electromechanical RCDs, I offer a photo with their “insides”. I would post an electronic RCD, some kind famous brand, and not Chinese, but, as I wrote above, ABB, Schneider Electric, Legrand and other serious manufacturers do not produce electronic RCDs.
RCD types AC, A, B
Depending on the type, the RCD must be disconnected from different types current leaks, there are RCDs that turn off only alternating current, there are RCDs that switch off alternating and pulsating current:
Reacts to instantaneous alternating differential leakage current, i.e. these are ordinary consumers: lighting, heated floors, refrigerators, convectors, etc. The type of RCD AC is indicated on the panel, these are either the letters AC, or a special symbol (pictogram) or both.
Reacts to both alternating and pulsating leakage current, which can slowly increase or occur suddenly. These are devices that use rectifiers and switching power supplies: computers, washing machines, televisions, dishwashers, microwave ovens, i.e. where everything is controlled by electronics. Some instructions for modern electrical appliances specifically indicate that it is necessary to install a type A RCD. The pictogram for a type A RCD looks like this 
RCD type A is more expensive than RCD type AC, because “covers” a larger protection zone. But it should be noted that the level of protection with an AC type RCD is higher than if there were no RCD at all.
PUE 7.1.78. In buildings, RCDs of type “A” can be used, which respond to both alternating and pulsating fault currents, or “AC”, which react only to alternating leakage currents. The sources of pulsating current are, for example, washing machines with speed controllers, adjustable light sources, televisions, VCRs, personal computers etc.
Readers often have a question: “Which RCD should I put on the refrigerator? washing machine, dishwasher, hob, etc.?” The most correct answer can be found in the instructions for household appliances.
But, for example, in Europe it is allowed to install only type A RCDs. AC type RCDs are prohibited.
RCD type B- a rarity in Russia, they are used in industry, where, in addition to other types of leaks, there are rectified current leaks; type B RCDs are not used in everyday life.
Trip delay (selectivity) RCD
Based on the response time, RCDs are divided into 3 types:
RCD without time delay, are used to protect people from electric shock and fire due to electrical wiring faults. An RCD without a time delay is installed on the lines of electrical receivers. And they are the first stage of defense.
RCD type S (selective), also called fire protection. This type S RCD operates with a delay (0.2-0.5 seconds), so it does not protect a person, but only protects against fires. Fire protection RCD installed at the beginning of the line after the opening machine and protects the input cable and the automation connection in the panel, and is also the second stage of the differential. protecting the entire house from fire.
You can determine that this RCD is selective by the letter “S” on the panel, which indicates that the RCD is selective with a time delay for shutdown.
Examples a single-phase selective fire protection RCD from ABB with a leakage current of 100 mA and a three-phase fire protection RCD at 300 mA from Schneider Electric.
RCD type S is selected with a rated leakage current of 100-300 mA. A fire RCD with a setting of 100-300 mA is the second stage of protection, and according to the rules, if several RCDs are installed on the same line in a circuit, then each subsequent stage must have a longer response time and current setting.
SP31-110-2003 p.A.4.2 When installing an RCD, selectivity requirements must be consistently met. With two- and multi-stage circuits, the RCD located closer to the power source must have tripping current settings and response time at least three times greater than that of the RCD located closer to the consumer.
If there were no time delay, and we have two RCDs on the line, one for 30 mA, the other for 100 mA, then in case of current leaks If both RCDs would trip and a 100 mA RCD would de-energize the entire house. Therefore, in order not to run out into the street in shorts in the cold and turn on the fire protection RCD in the street panel, fire protection RCD is selected with a setting sufficient to prevent fire.
RCD type G, the same as type S, only with a shorter time delay of 0.06-0.08 seconds. RCDs are rare, and I had to wait 2-3 months for their “arrival”, which is very inconvenient for me, because... electrical panels freeze for a long time.
RCD connection diagram
Power (electricity) can be supplied to both the lower and upper contacts of the RCD - this statement applies to all leading manufacturers of electromechanical RCDs.
Example from the instructions for the ABB F200 RCD
I share RCD connection diagrams for 2 types:
Connection diagram for a three-phase electric motor via an RCD
People often ask about connection in the comments. three phase motor(pump) through an RCD, the question arises due to the lack of three-phase electric motors neutral.
Actually, there is nothing complicated about this; for the correct operation of a three-phase RCD, we connect the neutral conductor to the neutral terminal of the RCD on the power side, and on the motor side it remains empty.
The RCD should be checked at least once a month. This is done quite simply, just click to the "TEST" button, which is available on any RCD.
The RCD must turn off; this should be done when the load is removed, when TVs, computers, washing machines, etc. are turned off, so as not to “tug” sensitive equipment again.”
I like ABB RCDs, which, like the ABB S200 series switches, have an indication of the on (red) or off (green) position.
Just like ABB S200 switches, there are two contacts on each pole at the top and bottom.
Thank you for your attention.
Residual current devices save a person from electrical injuries by removing voltage from electrical wiring when leakage currents occur through it. Invisible and uncontrolled violations of the insulation layer can cause enormous harm to our lives and property. Therefore, such protections are gradually gaining more and more popularity among the population.
Manufacturers produce these devices in a fairly large assortment and provide them with various electrical characteristics, which allow you to optimally select devices for the specific operating conditions of each electrical wiring.
The operation of RCDs on electronic components depends on the presence of voltage in the network. To turn off, power is required for the logic circuit with a built-in amplifier. For this reason, such devices are considered less reliable: they, as a rule, will not be able to perform their protective functions in the event of a zero break, when a phase potential has passed through the human body.
This option is shown in the picture: the power supply does not receive mains voltage, and the phase passes through the insulation breakdown to the washing machine body through the victim to the ground. The protective function cannot be performed due to design features device.
Electromechanical RCDs are triggered directly by leakage current, using no electrical energy supply network, and the potential of a pre-charged mechanical spring. Therefore, if a similar situation arises, they perform their protective function.
The picture shows the most difficult case for the operation of an electromechanical RCD connected to a two-wire circuit.
At the initial moment of the malfunction, the leakage current will pass through the human body, but after a short time required for the electromechanical device to operate, the phase potential will be removed from the circuit.
Since this period of time is less than the period of onset of cardiac fibrillation, we can assume that the protective function of the electromechanical RCD is fulfilled in this case.
It is quite natural that if in the considered examples the body of the washing machine is connected to a PE conductor, then:
the electronic circuit, as a rule, will not work either;
the electromechanical device will turn off the phase at the moment of insulation breakdown and thereby completely prevent the passage of current through the human body.
UZO-D
Please note that when describing the possibilities of switching off leakage currents by electronic RCDs, the addition “as a rule” was made. This is explained by the fact that now manufacturers have taken into account the shortcomings of previous designs and have launched the production of devices with power supplies that ensure the operation of the device when the voltage is removed from it.
Such RCDs are marked with the letter “D” and designated “UZO-D”. They can turn off the voltage when there is no power:
with a set time delay;
or without it.
At the same time, they are endowed with the ability to:
performing automatic reclosure (AR) of the circuit under load when voltage returns;
ban on automatic reclosing.
RCD-D can be equipped with selective operation conditions necessary for devices that use automatic transfer switching (ATS) when the main power supply line disappears. Such devices are marked with the letters S and G.
They differ in the length of the response delay. RCD-D type S has a longer time than type G.
The table of standard values of shutdown and non-shutdown times during RCD operation due to the appearance of differential current according to GOST P 51326.1-99 is presented in the picture.
To compare these values, you can use graphs created for a general type RCD with a residual current trip of 30 mA and a type S - 100 mA.
Type G devices operate with a response time of about 0.06÷0.08 seconds.
RCDs of type S and G make it possible to ensure the principle of selectivity for the formation of cascade protection circuits with unacceptable leakage currents and the creation of an algorithm for a specific queue for disconnecting consumers.
The second way to ensure selective operation of such devices is to select or adjust the setting of the differential element.
Load current passing through the RCD
On the body of each device and in the technical documentation, the value of the rated operating current of the device and protected consumers is indicated, according to which the design is selected. This numerical expression always corresponds to a number of rated currents of electrical equipment.
Each RCD is produced to process current of a certain vibration shape. In order to indicate this characteristic, lettering and/or graphic images of the type of device are made directly on the body.
RCD types A and AC respond both to a slow increase in differential current and to a fast, abrupt change in it. Moreover, the type of speaker is most suitable for use in ordinary household conditions because it is designed to protect consumers powered by alternating sinusoidal harmonics.
Type A devices are used in those circuits where the load is adjusted by cutting off part of the sinusoid, for example, by changing the rotation speed of electric motors with thyristor or triac voltage converters.
Type B devices work effectively where electrical equipment is used that requires the use of currents different shapes. Most often they are installed in industrial production and inside laboratories.
It should be noted that in recent years The number of electrical appliances with transformerless power supply has increased sharply. Almost all personal computers, televisions, and VCRs have switching power supplies; all the latest models of power tools are equipped with thyristor regulators without an isolating transformer. Various lamps with thyristor dimmers are widely used.
This means that the likelihood of a pulsating leak occurring DC, and, accordingly, human damage has increased significantly, which was the basis for the introduction of type A RCDs into widespread practice. In European countries, in accordance with the requirements of electrical standards, over the past few years, a widespread replacement of AC type RCDs with type A has been underway.
The residual current device is connected to operation together with a circuit breaker for protection against overcurrent. When choosing their ratings, you should take into account the fact that the machine is equipped with the functions of a thermal release and a shutdown electromagnet.
At currents exceeding the rated values of the circuit breaker by up to 30%, only the thermal release operates, but with a shutdown delay of about an hour. All this time, the RCD will be exposed to excessive load and may burn out. For this reason, it is advisable to use its denomination one value greater than that of the machine.
Marketers of manufacturers, for advertising purposes, began to provide RCDs with the function of protecting the connected electrical diagram from overloads and short circuit overcurrents. However, the electrician must understand that this is a different device called a differential circuit breaker.
Differential element setting
The choice of RCD based on leakage current limitation is important because it ensures safety conditions. Appliances operating in wet rooms must be connected to residual current devices set at 10 mA. For residential environments, selecting 30 mA is sufficient.
Protection of buildings from fire due to disruption of electrical wiring insulation is ensured by the operation of a differential element set to 100 or 300 mA, depending on the design and materials of the building.
All RCD devices can be divided into 2 conditional groups:
1. having the ability to adjust the setting of the differential body;
2. without settings.
Devices of the first group can be adjusted:
discretely;
However, regulation of the differential element operation for household appliances is not required. It is performed to solve problems of special electrical installations.
Number of poles
Since the RCD works by comparing the currents passing through the differential element, the number of poles of the device coincides with the number of current-carrying conductors.
In some cases, you can use a four-pole residual current device to operate on a two-wire or three-wire network. In this case, it will be necessary to leave free phase poles in reserve. The device will perform its functions, realizing its own capabilities not completely, but partially, which is economically unprofitable.
This method is used for emergency replacement of a faulty device or when installing a single-phase network, which will soon be converted to three-phase operation.
Installation method RCDs are manufactured in different housings for permanent installation in electrical wiring or with the possibility of use as a portable device equipped with a flexible extension cord.
Devices with Din-rail mounting are installed in electrical panels located in the entrance or apartment.
An RCD socket built into the wall ensures human safety when using any electrical appliance connected to it.
An RCD plug connected by a wire to one problematic device protects it when used in places with different environmental conditions.
Rated voltage
Residual current devices used in a single-phase network are produced for an operating voltage of 230 volts, and in a three-phase network - 400.
Additional features
The ability of RCDs to protect a person from exposure to electric current is constantly being improved by manufacturers. They are giving these devices more and more capabilities, connecting additional elements and accessories to them, and creating housings with different degrees of protection from environmental influences.
For example, there are known devices that are resistant to surge voltages due to the operation of a built-in varistor and those that cut off leakage currents in such situations.
RCD(Residual Current Device) is a switching device designed to protect electrical circuit from leakage currents, that is, currents flowing along undesirable, under normal operating conditions, conductive paths, which in turn provides protection from fires (electrical wiring fires) and from electric shock to humans.
The definition of “switching” means that this device can turn on and off electrical circuits, in other words, switch them.
RCD also has other names, for example: differential switch, differential current switch, (abbreviated as differential current switch), etc.
Design and operating principle of RCD
And so, for clarity, let’s present the simplest diagram of connecting a light bulb through an RCD:
The diagram shows that during normal operation of the RCD, when its moving contacts are closed, a current I 1 of value, for example, 5 Amperes from the phase wire passes through the magnetic circuit of the RCD, then through the light bulb, and returns to the network via the neutral conductor, also through magnetic circuit of the RCD, and the value of the current I 2 is equal to the value of the current I 1 and is 5 Amperes.
In such a situation, part of the electrical circuit current coming from the phase wire will not return to the network, but passing through the human body will go into the ground; therefore, the current I 2 that will return to the network through the magnetic circuit of the RCD along the neutral wire will be less than the current I 1 entering the network, Accordingly, the value of the magnetic flux F 1 will become greater than the value of the magnetic flux F 2, as a result of which the total magnetic flux will no longer be equal to zero.
For example, current I 1 = 6A, current I 2 = 5.5A, i.e. 0.5 Ampere flows through the human body into the ground (i.e. 0.5 Ampere is the leakage current), then the magnetic flux F 1 will be equal to 6 conventional units, and the magnetic flux F 2 will be 5.5 conventional units, then the total magnetic flux will be equal to:
F sums = F 1 + F 2 =6+(-5.5)=0.5 arb. units
The resulting total magnetic flux induces an electric current in the secondary winding, which, passing through the magnetoelectric relay, causes it to work, and it, in turn, opens the moving contacts, turning off the electrical circuit.
The functionality of the RCD is checked by pressing the “TEST” button. Pressing this button artificially creates a current leak in the RCD, which should lead to the RCD turning off.
RCD connection diagram.
IMPORTANT! Since the RCD does not have overcurrent protection, any circuit for its connection must also include an installation to protect the RCD from overload and short circuit currents.
RCD connection carried out according to one of the following schemes, depending on the type of network:
Connecting an RCD without grounding:
Connection diagram for RCD in the electrical network(when the neutral working and neutral protective conductors are separated):
IMPORTANT! In the coverage area of the RCD, you cannot combine the neutral protective (grounding wire) and the neutral working conductors! In other words, it is impossible in the circuit, after the installed RCD, to connect the working zero (blue wire in the diagram) and the ground wire (green wire in the diagram).
Errors in connection diagrams due to which the RCD trips.
As mentioned above, the RCD is triggered by leakage currents, i.e. if the RCD has tripped, this means that a person has come under voltage or for some reason the insulation of the electrical wiring or electrical equipment has been damaged.
But what if the RCD trips spontaneously and there is no damage anywhere, and the connected electrical equipment is working properly? Perhaps the whole point is one of the following errors in the network diagram of the protected RCD.
One of the most common mistakes is combining the neutral protective and neutral working conductors in the coverage area of the RCD:
In this case, the amount of current leaving the network through the RCD along the phase wire will be greater than the amount of current returning to the network through the neutral conductor because part of the current will flow past the RCD along the grounding conductor, which will trigger the RCD.
Also, there are often cases of using a grounding conductor or a third-party conductive grounded part as a neutral working conductor (for example, building fittings, a heating system, water pipe). This connection usually occurs when the neutral working conductor is damaged:
Both of these cases lead to the RCD tripping, because The current leaving the network through the phase wire does not return back to the network through the RCD.
How to choose an RCD? Types and characteristics of RCD.
To choose the right RCD and eliminate the possibility of error, use ours.
The RCD is selected according to its main characteristics. These include: 
- Rated current— the maximum current at which the RCD can operate for a long time without losing its functionality;
- Differential current— the minimum leakage current at which the RCD will disconnect the electrical circuit;
- Rated voltage- voltage at which the RCD can operate for a long time without losing its functionality
- Current type— constant (denoted by “-“) or variable (denoted by “~”);
- Conditional short circuit current- current that the RCD can withstand for a short time until the protective equipment (fuse or circuit breaker) trips.
RCD selection is based on the following criteria:
— By rated voltage and network type: The rated voltage of the RCD must be greater than or equal to the rated voltage of the circuit it protects:
Unom. RCD⩾ Unom. networks
At single-phase network required two-pole RCD, at three-phase network — four-pole.
— By rated current: according to clause 7.1.76. PUE, the use of RCDs in group lines that do not have protection from, without an additional device that provides this protection is not allowed, and a calculated check of the RCD in overcurrent modes is necessary, taking into account the protective characteristics of the higher-level device that provides overcurrent protection.
From the above it follows that in front of the RCD there must be a protection device (or) it is according to the current of this higher-level protection device that it is necessary to select the rated current of the RCD based on the condition that the rated current of the RCD must be greater than or equal to the rated current of the protection device installed before it:
I no. RCD ⩾ I nom. protection device
In this case, it is recommended that the rated current of the RCD be one step higher than the rated current of the higher-level protection device (for example, if a 25 Ampere circuit breaker is installed in front of the RCD, it is recommended to install the RCD with a rated current of 32 Amps)
For reference, standard values of RCD rated currents: 4A, 5A, 6A, 8A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, etc.,
— By differential current:
Differential current is one of the main characteristics of the RCD, which shows at what value of leakage current the RCD will turn off the circuit.
In accordance with paragraph 7.1.83. PUE: The total leakage current of the network, taking into account the connected stationary and portable electrical receivers in normal operation, should not exceed 1/3 of the rated current of the RCD. In the absence of data, the leakage current of electrical receivers should be taken at the rate of 0.4 mA per 1 A of load current, and the network leakage current at the rate of 10 μA per 1 m of phase conductor length. Those. The differential network current can be calculated using the following formula:
Δ I network =((0.4*I network)+(0.01*L wire))*3, milliampere
Where: Inetworks— network current (calculated using the formula above), in Amperes; Lwires— total length of the protected electrical network wiring in meters.
Having calculated ΔI network we accept the nearest higher standard value of the residual current of the RCD Δ I RCD:
Δ I RCD ⩾ ΔI network
The standard values of the residual current of the RCD are: 6, 10, 30, 100, 300, 500mA
Differential currents: 100, 300 and 500 mA are used for protection against fires, and currents: 6, 10, 30 mA are used to protect against electric shock. In this case, currents of 6 and 10 mA are used, as a rule, to protect individual consumers and, and a differential current of 30 mA is suitable for general protection of the electrical network.
If an RCD is needed to protect against electric shock, and according to the calculation, the leakage current is more than 30 mA, it is necessary to provide for the installation of several RCDs on different groups of lines, for example, one RCD to protect sockets in rooms, and a second to protect sockets in the kitchen, thereby reducing the most power passing through each RCD and, as a result, reducing the network leakage current, i.e. in this case, the calculation will need to be made for two or more RCDs that will be installed on different lines.
— By type of RCD:
There are two types of RCDs: electromechanical And electronic. We discussed the principle of operation of an electromechanical RCD above; its main working element is a differential transformer (magnetic core with a winding) that compares the magnitude of the current going into the network and the current returning from the network, and in an electronic device this function is performed by an electronic board that requires voltage to operate.
Read also:When you go to the store for a certain product, you probably know exactly what you need, what this product should be and for what purposes you will use it. The same applies to residual current devices and any other machinery or equipment. And before you buy an RCD in a store, you need to decide what type of device you need and for what load it will be used. In general, you need to decide on the parameters.
If you neglect some issues, it may turn out that devices of the same nominal value will work differently (or maybe not work at all) under certain circumstances.
Hello friends! I welcome all visitors to my website “Electrician in the House”. In today's article we will continue the topic related to residual current devices.
If you remember in the last article, we looked at how an electromechanical ouzo differs from an electronic one, and in today’s article I would like to address an issue that relates to their varieties. And to be more precise, varieties protective devices according to the type of current leakage - . Since this issue is also quite important and not everyone understands it.
Types of ouzo a and ac what is the difference
All residual current devices and differential circuit breakers are divided into several categories by type, for example, by internal design (electronic or electromechanical), time delay, number of poles, and type of differential current leakage. It is the last category that we will focus on. What does the type of RCD or RCBO mean by the type of differential current leakage?
Although we have alternating current in the network with a frequency of 50 Hz, however, the leakage current may not always be alternating. The leakage current can be variable, pulsating or constant, depending on what and where it is damaged.
To understand what is the difference between ouzo type A and AC let's determine for ourselves what each of them reacts to (what type of current):
An AC type RCD will only respond to alternating leakage current. The shape of the curve of such a current must be sinusoidal. In what situations does AC leakage current occur? Damage to the insulation inside any household appliance(washing machine, refrigerator, water heater, etc.) and phase contact with the housing. There can be a lot of situations. AC RCD is the most common and widespread; it can be used everywhere.
As we have already found out, AC RCDs are sensitive only to current that has a sinusoidal shape, so they are marked accordingly. An emblem in the form of a sine wave is applied to the body.
Type A RCD will respond to alternating and direct pulsating current leakage. As you understand, such protective devices are more sensitive than AC ones, but accordingly they cost a little more. We have found out how an alternating leakage current can appear, but where a constant pulsating leakage current can come from.
All modern technology is made using semiconductors (diodes, thyristors, converters, etc.). It is difficult to imagine a microwave or washing machine without electronic filling. Today, even energy-saving and LED lamps have a switching power supply inside. Do you remember how to connect led strip– via a switching power supply.
I once came across a statement on the Internet on one of the forums. One user wrote that RCD type A It will only be useful when someone disassembles live equipment and accidentally or intentionally puts their hand into the power supply. Like, what kind of fool would disassemble a washing machine or a refrigerator under voltage and touch its insides with his fingers?
But it is not at all unnecessary to disassemble something and touch the electronic board with wet hands. Everything has its own service life and your household appliances are no exception; everything breaks down and fails at some point. The secondary switching inside the power supply may be damaged and penetrate the metal case, resulting in a current leakage that RCD AC may not sense.
Sometimes it happens that the passport of electrical equipment directly states that its connection must be made only through a type A residual current device. Here, as they say, there are no options, you need to follow the instructions.
The curve of a direct pulsating current has the shape of half sine waves. Taking into account the fact that type A residual current devices operate on alternating and pulsating currents, they are marked on the housing as follows:
According to the requirements of electrical standards, European countries have long refuse RCDs with type AC and give preference to devices of type A. RCDs of type AC can be installed on equipment without electronics (water heaters, heated floors, etc.)
By the way, our PUE rules also say a few words, but there are no specific requirements in this regard. Both types can be installed. Here is what is written in PUE clause 7.1.78 7th edition:
What to install at home in the apartment uzo type a or ac It's up to you to decide, of course. I try to install RCD type A everywhere and recommend it to everyone.
Testing ouzo type a and ac, response difference
I think, in general terms, everyone understands what types of RCDs there are according to the type of operation and what is the difference between AC and A devices. Now I would like to conduct a little testing between these two types of RCDs to clearly show which type will react to what.
To provoke the operation of the protective shutdown device, we will create a leakage of direct pulsating current and see how our devices work or do not work.
We have already discussed how to create a sinusoidal leakage current and check the RCD at home in one of the articles on this site. The source of the constant pulsating leakage current will be a conventional rectifier diode, which is installed in almost every electronic equipment.
I bought a 1n5408 diode and will assemble a circuit using it to create a pulsating leakage current.
We apply an alternating voltage (sinusoidal) to the input of the diode, and at the output we remove a constant pulsating one. The shape of the curve will look like half-waves of a sine wave without changing its direction. Depending on the polarity of the diode connection (direct or reverse), a pulsating current will flow through the device in different directions.
We assemble the power supply circuit - diode - light bulb. To ensure correct operation, change the polarity of the diode.
First, let's check the electromechanical unit type A of the hager brand, which should sense such a leak. We create a leak through it using a diode and a light bulb. As you can see, the ouzo worked.
To be sure of reliable operation, we change the polarity of the diode. As we can see, in this case, the hager protective device coped with the task.
The second in our experiment will also be an ouzo made by Hager, but of the AC type, which in theory should not feel the pulsating leakage current at all. But in practice it turned out to be quite the opposite and the AC-type Uzo Hager also sensed leaks and switched off.
Moreover, this type of RCD worked at different polarities of the diode.
At first glance, it may seem that there is no difference between ouzo type a and ac, but in fact this is not the case.
The third in our experiment will be electromechanical ouzo from IEK. We assemble our circuit so that a leak appears through the ouzo. As can be seen from the photo, the IEK protective device does not sense the leakage of pulsating current.
The fact that the IEK ouzo did not turn off does not mean that it is defective or of poor quality. The thing is that this device is an AC type, as evidenced by the markings. Now I hope you understand difference between ouzo type a and ac.
Let's try to change the polarity of the diode connection. As you can see, in this version the ouzo worked.
If we open the catalog of any RCD manufacturer, we can read the following:
- RCD type "AC" protects only against leakage of alternating sinusoidal current;
- RCD type "A" protects against alternating current leaks and pulsed (pulsating) current leaks.
We all know that in our network an alternating sinusoidal current “flows” through the wires and all household consumers work from this network. Therefore, it seems like we can safely install “AS” type RCDs everywhere and not think about anything else. But is this true?
Let's take a close look at our modern home appliances, e.g. washing machine. It is plugged into a socket with an alternating sinusoidal voltage of 220-230V. If you look further, the alternating current consumed by it reaches the switching power supply through the power supply wire. Then the sinusoidal current is converted into another form. If you look at its graph, it will no longer be a sinusoid, but, for example, pulsed half-cycles. All this happens due to the presence of electronic semiconductor components in modern consumers. It is in such power supplies and after them that pulsed (pulsating) currents flow. So, if a non-sinusoidal current leak occurs, then the AC type RCD may not detect it and, accordingly, may not disconnect the damaged section of the circuit.
I would also like to note right away that all protective devices are tested at the manufacturer’s factories. RCD type "AC" is tested only for sinusoidal alternating current leaks. Manufacturers guarantee the correct operation of their "AC" type devices only against leakage of this kind of current. And the correct operation of the RCD is to disconnect the faulty section of the circuit when the leakage current reaches the setting of a specific RCD within a period of time that is safe for humans. An "AC" type RCD may trigger a pulse current leakage, but it can operate with a time delay and from a larger leakage current than the setting of a specific RCD. This can be very dangerous for humans.
Similar switching power supplies are found in almost every modern home consumer. If the equipment has something electronic (display, control unit, etc.), something in it is regulated (engine speed, time, operating mode, etc.), then we can safely say that it contains There is a switching power supply. Even if you disassemble fluorescent (energy-saving) lamps, you can find compact switching power supplies in them. This is exactly the type of household appliance that needs to be protected using an RCD type “A”.
Now let's move on to the evidence for the need to use a type "A" RCD for proper human protection.
The first evidence will be GOST R IEC 60755-2012 " General requirements to protective devices controlled by residual (residual) current." It has a very good plate B.1. It shows the current waveforms depending on electronic circuit consumer.
The left side shows simplest scheme electronic part of most household consumers, and the right side shows the shape of the differential leakage current. See the table below.
As you can see, in most cases, the use of an "AC" type RCD will be useless, since the differential leakage current will not have a sinusoidal shape.
Here is a screenshot from an ABB webinar showing a similar sign. It clearly shows that the use of RCDs of the "AC" type is not permissible in most cases. Next I will post this video. I recommend everyone to watch it from beginning to end.
There is also a good wording in the ABB catalog that RCDs of type “A” are intended for...
And in our modern home appliances, the physical quantity is necessarily regulated. This is the rotation speed of the drum in the washing machine, the fan speed and temperature in the air conditioner, the operating mode and temperature of the microwave oven, etc.
The second proof of the use of type “A” RCD is the passport (instructions) for the household appliance itself. To verify this, take and open it, for example, from your washing machine, dishwasher, microwaves, etc. Open the section “Connecting to the electrical network” and read what is written there. It strictly says that this equipment must be protected only with the help of an RCD type “A”. These are recommendations from the designers, engineers, and developers of these devices who produced them. These people know better than us how their device works, what currents flow in it, and therefore their demands must be followed unquestioningly.
Here is a clipping from the passport for the Bocsh washing machine. This pictogram indicates a type "A" RCD.
Of course, you will not find this recommendation in every passport. For some reason, some home manufacturers household appliances neglect this requirement and do not indicate it. But all famous European brands always pay special attention human safety and highlight this point in the “Connecting to the electrical network” section.
Below I suggest watching a webinar by a representative of the ABB concern, which talks about choosing the type of RCD “AC” or “A”. True, at the beginning it talks about the TN-C grounding system, but starting from the 54th minute a conversation begins about the choice of types of RCDs. I still recommend not to be lazy and watch the entire video, as there is a lot of useful information in it.
Who should you not listen to when choosing the type of RCD?
These are primarily managers and sellers of electrical goods stores. They always try to sell the goods that they have in stock, and RCD type “A” is not a warehouse item, especially in the regions of the country and is made to order. Also, many managers do not know what the difference is between types of RCDs “A” and “AC”. With these words I do not want to offend all sellers of electrical goods. Perhaps there are people working somewhere who understand the types of RCDs, but I have not met such people in Samara)))
Don't always rely on electricians' recommendations. Unfortunately, many also do not know the difference in this matter. Very often I have come across the phrase from electricians that there is no need to install an RCD at all, since it always trips. Don’t listen to your relatives and neighbor, who have had two machines for 20 years and everything works. Even today, YouTube has become very dangerous, since everyone is posting videos on it and, unfortunately, most of the videos do not carry the correct information.
Who should you listen to when choosing the type of RCD?
It is imperative to follow the recommendations from the equipment instructions. Watch webinars organized by large concerns such as ABB, Legrand, IEK, etc. Their videos contain a lot of useful and knowledgeable information. Webinars are conducted by leading engineers and equipment developers who know what they are talking about. On the official websites of large concerns you can find the schedule of webinars and their recordings. These are the ones I recommend for viewing.
Summarizing all of the above, we can conclude that RCD type "AC" can be installed to protect circuits to which resistive loads are connected, such as incandescent lamps, conventional hobs and ovens, conventional heaters, simple electric kettles. For all other equipment with electronic components, it is imperative to install a type “A” RCD.
This is precisely why I recommend that everyone who assembles electrical panels always choose an RCD of type “A”. If an RCD is installed in the switchboard, to which it is planned to connect several circuit breakers, then you definitely need to choose type “A”, since there is a high probability of electronic equipment being included in the network.
IMPORTANT!!! The same applies to the choice of automatic motors (RCBOs). They also come in "AC" and "A" types.
In Europe, only type “A” RCDs have been used in the residential sector for a long time, since only it can provide the necessary level of human safety. By following this link you can see an example of an electrical panel from Germany. All RCDs of type "A" are installed in it.
Unfortunately, in the budget series of protective devices there are no RCDs of type "A" with leakage currents of 10-30mA. They are only available in expensive and more professional series, for example, the F202 series from ABB or DX3 from Legrand. But if you compare different types The RCD is from the same series, then the difference in cost between “A” and “AS” is approximately 500 rubles.
Yes, type “A” RCDs have become very expensive today, but still, human life is more expensive!!!
Perhaps I am wrong in my conclusions. If so, then correct me. It will also be useful for me to imagine the whole real picture with the choice of an RCD of type “AC” or “A”. But, I made my conclusions by studying the relevant regulatory documents and recommendations from specialists from specialized companies.