What is ouzo in electrics and how to use it. What is an RCD and how does it work? Residual voltage cut-off device
- a specialized device used in domestic and industrial conditions (depending on the characteristics of a particular model) to turn off the current when its normal value is exceeded.
Additionally used to prevent possible electric shock, as well as fire in premises due to problems with wire insulation.
It should be noted that potential buyers often confuse this device with a circuit breaker. These devices are fundamentally different, although they are very similar in appearance.
It is not difficult for a specialist to distinguish these equipment from each other. RCDs have their own differences - in terms of rated current, electrical circuit, name on the case, abbreviation, and so on.
Features of practical operation
The RCD is used exclusively to disconnect in case of possible damage to electrical wiring and fire caused by insulation problems.
But the circuit breaker is capable of not only monitoring the current voltage value in the network, but also additionally protecting all wiring from the negative consequences of excess current.
If we consider the RCD from the point of view of the simplest language possible, the RCD only checks the network for leaks and the possible direction of current in the wrong direction (into electrical appliances).
If the system suddenly notices that the insulation is damaged and the voltage is flowing in the wrong direction, it will react instantly by turning off the network.
To achieve maximum safety, the RCD is connected in series with the machine.
It is noteworthy that if an overload is deliberately created, the RCD will not be able to operate. And the wiring itself will be damaged along with the system. By connecting zero and phase, deliberately causing a very strong short circuit, the RCD will also not work.
Thus, to which the residual current device is connected will protect against possible problems associated with overloads, leaks, and so on. Accordingly, all dangers will be quickly localized and prevented.
conclusions
If you wish to use an RCD, it can be used to achieve instantaneous disconnection in the network in the event of a leak. By using a series connecting circuit with a differential circuit breaker, you can get rid of not only the direction of current according to the wrong circuit, but also maintain the integrity of the wiring.
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Hello Dear reader of the site site. Today we’ll talk about RCDs for protecting people from leakage currents (residual current devices). RCD protection is installed in electrical networks to protect people from leakage currents and prevent fires.
Purpose
An RCD is an electrical device specially designed to cut off the power to electrical appliances during leakage currents. Leakage currents occur due to minor violations of the insulation of current-carrying phase conductors. If the insulation is broken, current begins to “flow” through the metal casings of electrical appliances or conductive structures of an apartment or house. Leakage current is also called differential current.
Since the leakage current is small in value, circuit breakers installed in the electrical network do not operate on it and do not turn off the power supply. Circuit breakers turn off the electrical network in the event of a short circuit in the network (touching a phase and neutral wire or two phase wires) or overload. Circuit breakers do not respond to small leakage currents.
Leakage current is a dangerous electrical fault for humans. For example, if you touch a conductor through which a current of 0.3 milliamps flows, you will feel an ant bite; with a current of 15 milliamps, it will be difficult to tear yourself away from the conductor, but it is still safe. This cannot be said about a current of 40 milliamps. When you “touch” such a leakage current, you are guaranteed to experience body and diaphragm convulsions, which is undoubtedly very life-threatening. RCDs are designed to protect people from leakage currents. Such devices must have a cut-off current of no more than 30 mA.
To protect the premises from fire, a general RCD is installed to protect people from leakage currents, with a cut-off current of 100 mA or 300 mA.
Installation standards
According to Russian standards, an RCD with a shutdown current of no more than 30 mA is installed for residential premises. The response time of the RCD, that is, the time from the appearance of leakage currents to the shutdown of the electrical circuit, should be in the range of 0.1-0.3 seconds; this shutdown time is sufficient to protect a person from death. But don’t think that with an RCD installed, you won’t feel the electric shock at all. There will be an electric shock, but the device must turn off the current in time and save your life.
I note that the same standards apply in Europe. In America, according to their National Electrical Code standard, RCDs installed in residential premises must have an operating current of 5 mA
Note: The serviceability of the device must be checked before installing the RCD, after installing the RCD, and every six months using the “Test” button on the case. If, when you press the “Test” button, the RCD works, that is, it turns off the network, then it is fully operational. If it doesn't work, it needs to be replaced.
Where is it necessary to install an RCD in the electrics of an apartment and house?
According to our regulatory documents, the RCD is an additional protection device. (PUE ed. 7, clause 1.7.50; clause 1.7.156).
Optional does not mean optional.
Installation of RCDs is carried out in all groups of the electrical circuit in which plug sockets are installed. The rated shutdown current of the device should be no more than 30 milliamps. At least one general Protective Disconnection Device for the entire apartment (house) must be installed.
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If you have an electrical network with many power supply groups, installing an RCD for each group together with a common RCD will only improve the safety of the living space. It is allowed to install one RCD on several separate power supply groups, provided that separate circuit breakers are installed on each group.
Selecting an RCD for human protection from leakage currents
The RCD has two main characteristics.
- Rated load current (in amperes)
- Rated cut-off current, also known as differential current (in milliamps).
RCD load current
The RCD must be installed in the electrical circuit together with overcurrent circuit breakers, after the circuit breaker. The rated operating load current of the device must be selected one point higher than the rating of the circuit breaker.
For example: Introductory circuit breaker for apartment 50 Ampere. This means that for the entire apartment, you need to install an RCD with a rated load current of 63 Amperes.
Rated cut-off current
for residential premises the rated cut-off current is selected:
- To protect people from leakage currents, an RCD with a cut-off current of 30 mA is installed;
- For wet areas (bathrooms) and children's rooms powered from a separate line, an RCD with a cut-off current of 10 mA is installed;
- To protect the house from fire, the cut-off current must be 100 mA or 300 mA;
- The choice of device is made on the basis of SP 31-110-2003.
Nominal cut-off time of RCD
- The nominal cut-off time should not exceed 0.2 milliseconds for a supply voltage of 230-400 Volts.
- In apartments and houses it is better to install an RCD of type “AC” or “A”. Type "AC" reacts only to sinusoidal, alternating, leakage currents. Type "A" reacts to sinusoidal and pulsating leakage currents. Pulsating currents arise from the operation of tape recorders, televisions, washing machines, and lighting controls.
RCD installation
- The device is installed after overcurrent protection circuit breakers.
- It is recommended to install the device in such a way that the phase and neutral working conductors are disconnected at the same time. In this case, the installation of an overcurrent protection circuit breaker on the neutral wire is not necessary.
- Below shows the correct and incorrect connections of the device in the apartment and house.
- In the top diagram, the device is installed immediately after the electric meter, without a circuit breaker. This is unacceptable (PUE 7.1.76).
It is forbidden install human protection against leakage currents in group circuits where there is no protection against overcurrents. On the source side, you need to install an overcurrent protection circuit breaker (ECP) in front of it.
Regulations
In these regulatory documents you will find information about RCDs for protecting people from leakage currents.
- PUE (Rules for Electrical Installations) ed.7
- SP 31-110-2003, Design and installation of electrical installations
- GOST R 50571.8-94, ELECTRICAL INSTALLATIONS OF BUILDINGS, Part 4
- GOST R 50571.11-96, Electrical installations of buildings, Part 7, Requirements for special electrical installations.
A residual current device (RCD) is an electrical low-voltage device that is used to automatically disconnect the protected section of the electrical circuit in the event of a differential current exceeding the permissible value for this device. You can also come across such an abbreviation as VDT - this is a differential current switch, that is, actually the same thing. In this article, we will look at the readers about the device, purpose and operating principle of an RCD used in electrical engineering.
Purpose
First, let's look at the purpose of the residual current device (in the photo below you can see its appearance). occurs in the event of a violation of the integrity of the cable insulation of one of the electrical wiring lines or in the event of damage to structural elements in a household electrical appliance. A leak can lead to either an operating household electrical appliance, as well as electric shock during operation of a damaged electrical appliance or faulty electrical wiring.
In the event of an unwanted leakage, the RCD in a fraction of a second disconnects the damaged section of electrical wiring or a damaged electrical appliance, which protects people from electric shock and prevents the occurrence of a fire.
The question is very often asked about... The difference between the first one is that this protective device, in addition to protection against electrical leakage (RCD functions), additionally has protection against short circuits, that is, it performs the functions of a circuit breaker. The residual current device does not have overcurrent protection, so in addition to it, circuit breakers are installed in electrical networks to implement protection.
Device and principle of operation
Let's look at the design of the residual current device and how it works. The main structural elements of the RCD are a differential transformer that measures the leakage current, a trigger element that influences the shutdown mechanism and the power contact release mechanism itself.
The operating principle of an RCD in a single-phase network is as follows. The differential transformer of a single-phase protection device has three windings, one of which is connected to the neutral conductor, the second to the phase conductor, and the third is used to fix the difference current. The first and second windings are connected in such a way that the currents in them are opposite in direction. In normal operation of the electrical network, they are equal and induce magnetic fluxes in the magnetic circuit of the transformer, which are directed counter to each other. The total magnetic flux in this case is zero and, accordingly, there is no current in the third winding.
In the event of damage to an electrical appliance and the appearance of phase voltage on its body, when touching the metal body of the equipment, a person will be exposed to leakage of electricity that will flow through his body to the ground or to other conductive elements that have a different potential. In this case, the currents in the two windings of the differential transformer RCD will be different, and accordingly, magnetic fluxes of different magnitudes will be induced in the magnetic circuit. In turn, the resulting magnetic flux will be different from zero and will induce in the third a certain value of current - the so-called differential one. If it reaches the triggering threshold, the device will work. We described the main ones in a separate article.
More information about how the RCD works and what it consists of is described in the video lessons:
Do you want to know how a residual current device works in a three-phase network? The operating principle is similar to a single-phase device. The same differential transformer, but it already compares not one, but three phases and the neutral wire. That is, in a three-phase protective device (3P+N) there are five windings - three windings of phase conductors, a neutral conductor winding and a secondary winding, through which the presence of a leak is detected.
In addition to the above structural elements, a mandatory element of the residual current device is a testing mechanism, which is a resistor connected via the “TEST” button to one of the windings of the differential transformer. When you press this button, the resistor is connected to the winding, which creates a difference current and, accordingly, it appears at the output of the secondary third winding and, in fact, simulates the presence of a leak. Triggering of the residual current device indicates that it is in good condition.
Below is the symbol of the RCD in the diagram:
Application area
The residual current device is used to protect against current leakage in single-phase and three-phase electrical wiring for various purposes. In a home, an RCD must be installed to protect the most dangerous household electrical appliances from the point of view of electrical safety. Those electrical appliances, during the operation of which there is contact with metal parts of the housing either directly or through water or other objects. First of all, this is an electric oven, washing machine, water heater, dishwasher, etc.
Oleg Udaltsov
Eaton Power Distribution Components Product Specialist.
What is a residual current device
A residual current device, also known as an RCD, is a device installed in an electrical panel in an apartment or house to automatically turn off the power supply in the network in the event of a ground fault current.
Ground fault current occurs in wiring and/or electrical appliances when the insulation in them is broken for some reason or when exposed parts of the wires that should be secured in the terminals, for example inside household electrical appliances, touch the housing of the devices - and the current begins to “leak” in an undesirable direction.
This can lead to a fire due to overheating (first of the wiring or device, and then of everything around it) or to the fact that a person or pet will suffer from the current - the consequences can be extremely unpleasant, even death. But this will only happen if you touch a conductor or equipment body that is energized.
The main difference between an RCD and a conventional circuit breaker is that it is designed specifically to interrupt ground fault current, which the circuit breaker is not able to detect. An RCD can turn it off in a fraction of a second, before the moment when it becomes dangerous to a person or property.
Where and how much to install
For one- and two-room apartments - to the common electrical panel of the apartment. If the housing area is large, then in several local electrical panels distributed throughout the house.
An RCD will be required for the entire system for protection against, as well as for individual lines supplying groups of electrical appliances with a metal body (washing machine, dishwasher, electric stove, refrigerator, etc.) - for protection against electric shock. If a malfunction appears or an accident occurs, not the entire apartment will be de-energized, but only one line, so it will be easy to determine the culprit for tripping the RCD.
However, we must keep in mind: neither RCDs nor conventional automatic machines can save you from an electric arc or arc breakdown.
An electric arc can occur when, for example, the wire from an electric lamp is often pinched by a slamming door and the metal part of the wire inside is damaged. At the site of damage, a spark hidden from view will occur, accompanied by an increase in ambient temperature and, as a result, ignition of nearby flammable objects: first the wire sheath, and then wood, fabric or plastic.
To protect against such hidden threats, it is better to choose solutions that combine the functions of a machine, RCD and arc flash protection. In English, such a device is called arc fault detection device (AFDD), in Russia the name “arc fault protection device” (AFDD) is used.
An electrician may be able to include such a device in the design if you tell him that you need a higher degree of protection. For example, for a children's room, where a child can handle wires carelessly, or for groups of sockets for powerful electrical appliances with flexible wires that are prone to breaking.
It is equally important to install protection devices where wiring is laid openly and can be damaged. And also when planned, to avoid risks in case of accidental damage to hidden electrical wiring while drilling walls.
How to choose
A good electrician will recommend an RCD manufacturer and calculate the load, but you need to be sure that the recommendations are correct. And if you purchase everything yourself for repairs, then even more so you need to understand what to look for when choosing a device.
Price
Do not purchase a device in the lower price range. The logic is simple: the higher quality the components inside, the higher the price. For example, some cheap devices do not have burnout protection, and this can lead to fire.
A cheap device can be made of fragile materials and can easily break when you lift up the lever that is lowered when triggered. According to the standard, the RCD must be designed for 4,000 operations. This means that you will only have to make a choice once, but only if you have purchased a quality product. By purchasing a low-quality device, you put yourself and your loved ones at risk, not to mention material losses in the event of a fire.
Case quality
Pay attention to how tightly all parts of the device fit together. The front panel should be monolithic and not consist of two halves. The preferred material is heat-resistant plastic.
Device weight
Give preference to heavier devices. If the RCD is light, it means that the manufacturer has saved on the quality of internal components.
Conclusion
It is advisable to involve professionals to resolve issues related to electrical systems in the home. However, the responsibility should not be placed entirely on their shoulders. It is better to be guided by the proverb “Trust, but verify.” Having even basic knowledge of the subject and understanding the scenario for the future use of electrical appliances in the house, you can protect yourself and your loved ones from problems with electricity.
A residual current device, further referred to as an RCD, is designed to protect a person from electric shock, as well as from a fire that can occur when an electric current leaks due to poor insulation or poor connection of electrical installations (EU).
The RCD should operate, that is, open the contacts, thereby completely stopping the supply of voltage to the protected line, provided:
1 Human contact with non-current-carrying parts of the power plant that are energized due to insulation breakdown.
2 Human contact with live parts of the power plant that are energized.
3 Occurrence of (differential) leakage current to the power plant housing or ground to prevent fire.
Operating principle of RCD. Scheme
Rice. 1
1
Differential current transformer
2
Trigger element
3
Actuating mechanism
4
“Test” button to check the serviceability of the RCD
I 1 – I 2 direction of current relative to load
I D – leakage current
Ф 1 – Ф 2 magnetic fluxes
Purpose of blocks.
1
Differential current transformer(used in most RCDs) measures the balance of currents between the conductors entering it.
2 Trigger element(consists, as a rule, of electromagnetic relays) serves to control (influence) the actuator.
3
Actuating mechanism Designed for emergency shutdown of an electrical circuit controlled by an RCD.
4
“Test” button to monitor the serviceability of the RCD by creating a leakage current simulation.
Operating principle of residual current device (RCD)
Electrical circuit diagram
Rice. 2
1, 2 Primary windings
3 Secondary winding
If the controlled line is in good condition, there is no specified leakage current, and the transformer is in a state of rest (equilibrium), because the currents in the oppositely connected primary windings of the transformer are equal. Due to the fact that equal magnetic fluxes moving towards each other are mutually subtracted (that is, equal to zero), no electromagnetic field arises in the secondary coil, which means there is no voltage and no emf arises capable of influencing the relay on the basis of which the trigger mechanism is assembled (Fig. .1 ).
And as soon as a leak occurs on the protected (controlled) line equal to the RCD response value (usually from 10 to 30 mA), then the equality in the primary windings of the transformer is violated. As a result, an electromagnetic field arises in the primary and secondary coils, which forms a voltage coupling. That is, in the secondary winding a relay operating voltage arises (Fig. 2), which makes up the starting element (Fig. 1), the effect of which on the actuator (Fig. 1) turns off the contact group, thus de-energizing the protected line.
Attention!
It should be remembered that the RCD requires monthly testing, which is carried out by pressing the “Test” button. In this case, the electrical circuit closes, emitting an artificial current leakage and triggering the protective shutdown device. Failure to operate will indicate a complete malfunction of the device.
According to modern requirements, all electrical installations must have or. In this case, a specified leak that occurs will automatically disable the protection.
An example of this can be seen in the diagram in Fig. 3
Rice. 3
If we imagine differential protection in the form of a simple mechanical device like a scale (Fig. 4) with a response threshold of up to 10 mA. It immediately becomes clear that when the value of 10 mA is reached on one of the scales, they will go out of balance, the contacts will open and the controlled (protected) line will be de-energized. Moreover, we note that the center of balance of the scales is precisely or, therefore it is they that must be used so that the person himself is not this center.
Attention!
You also need to understand that the RCD is an additional safety measure that responds only to differential current (leakage current) and does not respond to short circuits and line overload. Therefore, as a rule, RCDs are installed together with circuit breakers that respond to short circuits (short circuits) and line overloads for which they are designed.
Visual electrical diagram for connecting an RCD
Rice. 5
RCD. Video explanation
Selecting an electromechanical RCD
I wish you successful installation and remember electrical safety.
DIFFERENTIAL SWITCHES type VD1-63 (UZO). Manual
Passport
3421-033-18461115-2007 RE, PS
1 Purpose and scope
1.1 Automatic switches controlled by differential current, without built-in overcurrent protection, functionally independent of the network voltage for household and similar applications, type VD1-63 (UZO) of the IEK® trademark (hereinafter referred to as VD) are intended for operation in single-phase or three-phase AC electrical networks current voltage up to 400 V frequency 50 Hz
and their characteristics correspond to GOST R 51326.1 and technical specifications TU 3421 -033-18461115-2002.
1.2 VDs perform the function of detecting differential current, comparing it with the value of the differential operating current and disconnecting the protected circuit in the case when the differential current exceeds this value. VD provide:
— protection of people from electric shock through indirect contact with accessible conductive parts of electrical installations in the event of insulation damage (VD with a rated differential current of 10, 30 and 100 mA);
- protection against fires arising as a result of fire insulation of live parts of electrical appliances from differential (residual) current to ground or due to prolonged flow of damage current in the event of failure of overcurrent protection devices (VD with a rated disconnecting differential current I D n = 300 mA);
— VDs having a rated differential switching current of no more than 30 mA can be used as a means of additional protection in the event of failure of devices designed to protect against electric shock.
1.3 The main area of use of VD is accounting and distribution boards of residential and public buildings, temporary power supply devices for construction sites, garden houses, garages, retail facilities.
2 Main characteristics
2.1 The main characteristics of the VD are given in Table 1.
Table 1
| Characteristic name | Meaning | ||
| Number of poles | 2 | 4 | |
| Rated operating voltage Ue, V | 230 | 230, 400 | |
| Rated network frequency, Hz | 50 | ||
| Operating voltage range of the operational control device, V | from 115 to 265 | from 200 to 460 | |
| Rated current In, A | 16, 25, 32, 40, 50, 63, 80, 100 | ||
| Rated residual current I D n, mA | 10, 30, 100, 300 | ||
| Rated non-tripping differential current I D n o , mA | 0.5 I D n | ||
| Rated maximum making and breaking capacity Inm, A | 1000 | ||
| Rated maximum differential making and breaking capacity I D m , A | 1000 | ||
| Rated conditional short circuit current not less than, A | 3000 | ||
| Rated conditional differential short-circuit current I nc, not less, A | 3000 | ||
| Characteristics of operation in the presence of differential current with a DC component, type | AC | ||
| Electrical wear resistance, on-off cycles (O-O), not less | 4000 | ||
| Mechanical wear resistance of B-0 cycles, not less | 10 000 | ||
| Maximum cross-section of the wire connected to the power terminals, mm 2 | 50 | ||
| Presence of precious metals, silver, g | 0.25 (per contact) | ||
| Climatic modification and placement category according to GOST 15150 | UHL14 | ||
| Degree of protection according to GOST 14254 | IP20 | ||
| Service life, at least, years | 15 | ||
2.2 The values of the maximum HP shutdown time in the presence of differential current are given in Table 2.
table 2
Attention! The VD does not have built-in overcurrent protection, so it is necessary to connect in series with it a circuit breaker of the same or lower rating with type B and C overcurrent protection characteristics.
2.3 Overall and installation dimensions are shown in Figure 1.
2.4 Electrical circuit diagrams of the VD are shown in Figures 2 and 3.
2.5 The use of VD in apartment and floor switchboards in electrical installations with grounding systems TN-S, TN-C-S, TN-C is regulated in GOST R 51628.
3 Completeness
Package Included:
- VD - 1 piece;
- packing box - 1 pc.;
- instruction manual and passport - 1 copy.
4 Installation and operation
4.1 Installation, connection and commissioning of the HP must be carried out only by qualified electrical personnel.
4.2 The VD is installed on a 35 mm wide mounting rail (DIN rail) in electrical panels with a degree of protection in accordance with GOST 14254 of at least IP30.
4.3 After installation and checking its correctness, apply mains voltage to the electrical installation and turn on the high-pressure motor by moving the control handle to the “I” - “ON” position, press the button
"TEST". Immediate operation of the VD (switching off the circuit protected by the device) means that the VD is operational.
4.4 If, after turning on the high pressure motor, it turns off immediately or after some time, it is necessary to determine the type of malfunction in the electrical installation in the following order:
a) cock the HP using the control handle. If the VD is cocked,
this means that there was a current leak to the ground in the electrical installation caused by an unstable or short-term insulation failure. Check the operation of the HP by pressing the “TEST” button;
b) if the air pressure is not cocked,
this means that in the electrical installation there is a defect in the insulation of any electrical receiver, electrical wiring, installation conductors of the electrical panel or the VD is faulty.
In this case, you need to do the following:
— turn off all electrical receivers and cock the HP. If the HP is cocked, this indicates the presence of an electrical receiver with damaged insulation. The malfunction is detected by connecting electrical receivers in series until the VD is triggered. The damaged electrical receiver must be disconnected. Check the operation of the HP by pressing the “TEST” button;
— if the HP continues to operate when the electrical receivers are turned off, it is necessary to call a qualified electrician to determine the nature of the damage to the electrical installation or identify the HP malfunction.
The test is carried out by pressing the “TEST” button. Immediate activation of the high pressure motor and shutdown of the protected electrical installation means that the high pressure motor is in good working order.
4.6 Operating conditions:
— range of operating ambient temperatures - from -25 to + 40 °C;
— altitude above sea level - no more than 2000 m;
— relative humidity - 90% at 20 °C;
— working position - any; . - mechanical group
execution - M1 according to GOST 17516.1.
5 Safety requirements
5.1 According to the method of protection against electric shock, VD corresponds to class 0
according to GOST 12.2.007.0 and must be installed in distribution equipment with a protection class of at least 1.
