Is it necessary to put an ouzo in the apartment. Why you need a residual current device for your home and how to choose one. Where and how much to install
) is not universal remedy protection of electrical circuits. RCD is a device that supplements the basic protection electrical circuit(protection against overcurrent short circuit and overload). The RCD cannot turn off the network when overloaded. If there is only one RCD in the circuit, then when overloaded, it will simply burn out. True, it is worth noting that instantaneous RCDs can act as additional protection against overcurrents in case of short circuit.
Note: This article discusses the rules for installing an RCD. The installation of automatic differential current circuit breakers (RCBOs) of the UZO-D type is not considered.
RCD installation rules - residual current device
The rules are formulated as they are significant and binding. The list is ranked from mandatory to recommended.
2. An RCD is installed in the floor or;
3. RCDs without built-in protection must be installed together with circuit breakers (). Circuit breakers will protect the RCD from burnout during overload and short circuit;
4. RCD not installed on a wiring group without a circuit breaker. The tripping current of the circuit breaker must be no more than the rated current of the RCD. For example, a 40 Amp RCD should be protected by a 36 Amp circuit breaker, in extreme cases, 40 Amperes;
5. A circuit breaker in a circuit with an RCD can be either single-pole (per phase) or two-pole (phase + zero) and it must be installed before the RCD from the power supply side;
Explanations for the diagram: RCD 3 is protected by circuit breaker 1 and is installed for three groups with circuit breakers 4, 5, 6.
6. You can install one RCD on several, provided that each of the groups is protected by a separate circuit breaker;
7. If you plan to install several RCDs, then for each RCD, at the output, you need to install your own zero bus, separate from the others;
More rules
It could be said about the prohibition of grounding of instrument cases and ground contacts of power outlets in the RCD coverage area. But I will say differently: Forget about zeroing in the apartment and house. It's dangerous, inefficient, and unnecessary. If the house has a "clean" system grounding TN-C forget about RCD and zeroing.
For electrical circuits in wet rooms (bathroom, etc.), the installation of an RCD with a tripping current of not more than 30mA is mandatory. It is better to install an RCD with a trip current of 10mA;
It is better to install RCD 30mA on separate household appliances in contact with water ( washing machine, dishwasher);
Do not confuse the RCD terminals zero (N) and phase (L). The N terminal of a two-pole RCD is located on the right side of the device and is usually marked with the corresponding letter;
Both the top and bottom terminals of the device can be used for input. But for the order and uniformity of installation, I advise you to do a classic installation: input at the top, output at the bottom of the device;
I repeat, each RCD circuit should have its own zero pad. All working neutral wires of this group are connected to this block, and not to the main zero block of the network. That is, they put the RCD immediately to it with their zero block. The outgoing zero from the RCD was brought to this block and to it all the zeros of this group;
In order to protect the electrical network of a house or apartment, circuit breakers or fuses are used. These elements allow you to avoid fire during a short circuit, but are completely unable to protect against impact. electric shock. Product for protective shutdown electricity, the principle of operation of which is aimed at preventing current leakage to the device case, allows you to instantly de-energize the entire home network if the phase current is outside the "allowed" section of the conductor.
The use of RCDs allows you to protect not only the home electrical network, but also powerful three-phase installations in production. Why install such electrical products and how to do it correctly will be described in detail below.
Why do you need an RCD in an apartment
In old apartment buildings, often in the wiring there is no third protective conductor, in which there should be grounding. With this wiring diagram, powerful appliances, the “mass” of which is connected to the grounding terminal of the socket, are not protected, and if a phase current leaks to the case, the device can pose a serious threat to life and health. If you install an RCD in an apartment that is not equipped with a grounding conductor, then in the event of an electricity leak, the home electrical wiring will not be automatically disconnected from the mains.
As a rule, the impact of current, when a person touches the body of the device, in this case will be negligible time, so the negative manifestation of dangerous voltage is practically not observed.
If the apartment is connected to a common ground, then there will be an automatic power outage at the moment when there is a “breakdown” to the housing.
Why you need an RCD in an apartment is now clear, but why use this device for private households?
RCD in a private house
Many private developers do not understand why an RCD is needed in a house, because such an object can be easily equipped with high-quality grounding, which will ensure the “utilization” of dangerous voltage from the body of any electrical appliance. So why do you need a residual current device in a private house?
Connecting a high-quality grounding conductor allows you to protect a person from severe electrical injury when touching the case on which a leak has occurred, but in this case, the current does not turn off, and an electric arc can form between the “ground” and the phase, in the device itself, which is often the cause of the fire.
To protect the internal conductors from such an effect, it is necessary to disconnect all devices equipped with a ground wire from the outlet after use, or you need to put an RCD in the circuit electrical appliance. Next, we will talk about why to install a protective device in the bathroom.
RCD in the bathroom
The bathroom should also have an electric shock protection device installed. Even if the bathroom is located in an apartment or house that is not equipped with grounding, the device will still turn off the electricity supply at the time of a leak. So why should you install a safety device in the bathroom?
To maximize the effectiveness of this safety mechanism, choose a model with a sensitivity of 30 mA or less. If powerful appliances are not connected in the bathroom, then ideal option for a room with high humidity, there will be installation of a protective product with a leakage current of 10mA. Such devices will cost much more, but their use will make it possible to protect people from the effects of electricity as much as possible. Why is it easy to understand, but why install protection on lighting fixtures?
RCD for lighting
RCD for lighting must also be installed in accordance with all the rules. Why this should be done will be discussed later. Even in the case when the phase wire was put through the switch, you need to install protective article for the whole chain lighting device, after all, an emergency power outage may be necessary, with non-standard operation of the lamp.
For example, a heavy chandelier can come off and, together with the light bulbs on, fall on people. At this point, it is guaranteed that there will be a power outage if it leaks. Will protect the product from electric shock and in damp rooms with a low ceiling.
For example, in a damp basement, it is imperative to install a device that will turn off the supply of electric current to the lighting element at the moment
when a person touches the damp insulation of the conductor or lamp socket.
It is also necessary to equip all street lamps with a protective device, because the operation of such products takes place in very unfavorable conditions of heat, high humidity or low temperatures, in winter time. Despite the increased protection of street lamps from moisture, over time from mechanical damage, or for other reasons, it can become significantly thinner insulating layer, and the metal surface
lighting device will be under life-threatening voltage.
Why install a protective mechanism for lighting is understandable, but why an RCD for a three-phase network if its function can be replaced by powerful circuit breakers?
RCD for a three-phase network
All equipment operating from a three-phase network must also be connected to a protective power outage system. The amount of leakage current in such networks can be too high, so these products do not protect a person from an electric shock, but they allow you to turn off electricity consumers when a phase breakdown occurs to the "ground" of the device. Thus, it is possible to completely eliminate the possibility of a dangerous electrical potential appearing on the instrument case. This wiring diagram can only be connected if there is protective earth in the wiring of a house or apartment.
Why install an RCD is described in detail above, but where is the best place to place this device?
Where to install RCD
The system of protective shutdown of electricity must be installed in such a way that the power of the connected devices to electrical network was not higher than the maximum allowable for this RCD model, for which, before carrying out installation work refer to the instruction manual for the protective device.
For better quality and reliable protection home electrical wiring, you need to install one device of greater power in the shield, and equip the bathroom and other most dangerous, in the electrical sense, rooms with additional devices with a lower leakage current. If you need to install a protective device for a free-standing powerful electrical appliance with a metal case, then installation work can be carried out in the immediate vicinity of the protected object. In this case, the most suitable model there will be a protective product that has a built-in circuit breaker. The installation of such an RCD allows not only to ensure the minimum probability of electric shock, but also to protect the electrical circuit from a short circuit.
Why is it necessary to install an RCD in an electrical circuit, and why do this in accordance with the safety regulations and the operating manual for this device? Many home craftsmen do not understand why this is necessary and pay with serious consequences, because electric shock is a fairly common cause of death not only for people whose profession is connected with electricity, but also for ordinary users of home appliances.
Usually, many home craftsmen no longer care about the question: “Why do I need to install a protective device”, after they feel the effect of an electric current of 220 V. Why this should be done according to the rules, choosing a protective device for power, is also often found out through trial and error.
The purpose of the RCD and its use is to save human life, therefore, in some countries of the European Union, such protection is mandatory for installation in private households. It is desirable that this rule be introduced in our country, then the number of accidents will be significantly reduced.
A residual current device (RCD) is an electrical low-voltage device that serves to automatic shutdown protected section of the electrical circuit in the event of a differential current exceeding the permissible value for this machine. You can also find such an abbreviation as VDT - this is a differential current switch, that is, in fact, the same thing. In this article, we will consider with readers what device, purpose and principle of operation of the RCD used in electrics.
Purpose
First, let's consider what the purpose of the residual current device is (in the photo below you can see its appearance). occurs in case of violation of the integrity of the cable insulation of one of the wiring lines or in case of damage structural elements in a household appliance. Leakage can result in a household appliance being used or in use, as well as an electric shock during operation of a damaged appliance or faulty electrical wiring.
RCD in the event of an unwanted leakage in a fraction of a second, disconnects damaged area electrical wiring or a damaged electrical appliance, thereby protecting people from electric shock and preventing a fire.
Very often the question is asked about. The difference between the first is that this protective device, in addition to protection against leakage of electricity (RCD functions), additionally has protection against short circuits, that is, it performs the functions circuit breaker. The residual current device does not have overcurrent protection, therefore, in addition to it, circuit breakers are installed to implement protection in electrical networks.
Device and principle of operation
Consider 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 starting element that acts on the tripping mechanism and directly on the disconnection mechanism of the power contacts.
The principle of operation of the 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, and the third serves to fix the differential current. The first and second windings are connected in such a way that the currents in them are opposite in direction. In the normal mode of operation of the electrical network, they are equal and induce magnetic fluxes in the magnetic circuit of the transformer, which are directed towards each other in the opposite direction. The total magnetic flux in this case zero and, accordingly, there is no current in the third winding.
In the event of damage to the electrical appliance and the appearance of phase voltage, when touching the metal case of the equipment, a person will be exposed to leakage of electricity, which will flow through his body to the ground or to other conductive elements with a different potential. In this case, the currents in the two windings of the RCD differential transformer will differ, and, accordingly, magnetic fluxes of different magnitude will be induced in the magnetic circuit. In turn, the resulting magnetic flux will be different from zero and will induce a certain value of current in the third - the so-called differential. If it reaches the trigger threshold, the device will trigger. We have 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 the residual current circuit breaker works in three-phase network? The principle of operation is similar to a single-phase device. The same differential transformer, but it already compares not one, but three phases and neutral wire. That is, in a three-phase protective device (3P + N) there are five windings - three windings of phase conductors, a winding of a neutral conductor and secondary winding which detects the presence of a leak.
In addition to the above structural elements, an obligatory element of the residual current device is a test mechanism, which is a resistor connected through the “TEST” button to one of the windings of the differential transformer. When this button is pressed, the resistor is connected to the winding, which creates a differential current and, accordingly, it appears at the output of the secondary third winding and, in fact, simulates the presence of a leak. The operation of the residual current device indicates its good condition.
Below we give symbol RCD on 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 RCD, it should without fail be installed to protect the most dangerous in terms of electrical safety household electrical appliances. Those electrical appliances, during the operation of which there is contact with the metal parts of the body directly or through water or other objects. First of all, it is an electric oven, a washing machine, a water heater, Dishwasher and etc.
Let's see, is it necessary to install an RCD?
Recently, on the forums you can see questions from consumers of electricity, and is it necessary to install an RCD when designing new wiring. If the installation of a residual current device is prescribed in specifications connection, then the installation of an RCD is required. Without installing an RCD, the power supply organization simply will not give you permission to connect, and the specialist you called to seal the meter will simply not sign the act and seal the meter if the implemented power supply scheme differs from the scheme in the technical conditions for connection.
However, keep in mind that in accordance with the PUE (Electrical Installation Rules), RCD is an additional protection.
Item 1.7.50. Electrical Installation Rules (Section 1 as amended in 2003):
To protect against electric shock in normal operation, the following protective measures against direct contact must be applied individually or in combination:
basic insulation of current-carrying parts;
enclosures and shells;
setting up barriers;
placement out of reach;
the use of ultra-low (small) voltage.
For additional protection against direct contact in electrical installations with voltages up to 1 kV, if there are requirements of other chapters of the PUE, residual current devices (RCDs) with a rated differential breaking current of not more than 30 mA should be used.
Clause 7.1.72. Electrical Installation Rules (Section 7 as amended in 2002):
If the overcurrent protection device (circuit breaker, fuse) does not provide an automatic trip time of 0.4 s at a rated voltage of 220 V due to low values short-circuit currents and the installation (apartment) is not covered by the potential equalization system, the installation of an RCD is mandatory.
Clause 7.1.76. Electrical Installation Rules (Section 7 as amended in 2002):
7.1.76. It is recommended to use an RCD, which is a single device with a circuit breaker that provides overcurrent protection.
It is not allowed to use RCDs in group lines that do not have overcurrent protection, without an additional device that provides this protection.
When using RCDs that do not have overcurrent protection, their design verification in overcurrent modes is necessary, taking into account the protective characteristics of the higher-level device that provides overcurrent protection.
There is a clause in the rules that also prohibits the installation of an RCD.
Clause 7.1.77. Electrical Installation Rules (Section 7 as amended in 2002):
In residential buildings, it is not allowed to use RCDs that automatically disconnect the consumer from the network in the event of a power failure or unacceptable drop in mains voltage. In this case, the RCD must remain operational for a time of at least 5 s when the voltage drops to 50% of the nominal.
Among other things, if the group line feeds a fire or burglar alarm, then the installation of an RCD, as a protection device in such a network, is also prohibited.
When deciding whether it is possible to do without an RCD, it is always necessary to take into account various factors that can affect the safety of a network without an RCD. The residual current device, although it is an additional protection, it primarily protects against the occurrence of so-called touch currents. Those. no circuit breaker will protect you from electric shock. RCD - on the contrary, when touched, it will de-energize the protected section of the network.
RCDs should be installed in rooms where the possibility of electric shock is greater compared to ordinary premises. Those. these are rooms with high humidity, the presence of metal floors, scaffolding, etc.
Among other things, in the event of damage to the insulation of the electrical wiring in the walls, a leakage current also occurs, which is sufficient to trigger the RCD. In this case, when the damage to the network is not obvious, or it is very difficult to find it, it is necessary to understand that if the RCD is excluded from the circuit as a whole, the performance of the group network will not be affected, however, there is the possibility of insulation damage developing into a short circuit, or obvious heating of the conductors in the place leakage, which may cause a fire.
How can you sum up the above? RCD is a protection device, which means it ensures your safety. If the network at home is highly distributed, and the resulting cumulative leakage current in normal mode leads to the operation of the RCD, then it is better to divide such a network into sections and install additional RCDs than to abandon it altogether. Moreover, the cost of an RCD is currently comparable to the cost of a circuit breaker. It's better not to risk it.
The residual current device monitors the differences in currents flowing through two wires of a single-phase network and four wires of a three-phase network. If the sum of these currents is zero, then the RCD is operating normally. If there is a difference in currents (differential current), then the RCD turns off the section of the network on which the device is installed.
The main purpose of the RCD is protection against electric shock when touching the conductive housings of devices that are energized (protection against indirect contact).
If the body of the device, potentially conducting current, for example, a washing machine, accidentally becomes energized, then when it touches, the RCD of this section should turn off the damaged section of the circuit. The RCD can be triggered not only when fault currents occur (if the insulation is damaged), but also when the phase wire touches the conductive housing directly.
After the RCD trips, it is necessary to eliminate the malfunction and cock the RCD to working position by lifting the control lever up.
RCD features
The protective shutdown device is distinguished by high sensitivity. For the electrical wiring of the apartment, RCDs with tripping currents of 10mA and 30mA are used. Such a high sensitivity of the device greatly increases the electrical safety of residential wiring. RCDs with cutoff currents of 100mA and 300mA are designed to increase fire safety premises and are installed at the power input to the house.
Residual current device for fire safety
Let me explain about the protection of RCDs from fires. For example, consider the opening shield in a private house. Over time, a layer of dust develops in and around the shield. Also, over time, isolation input cable changes its properties and begins to collapse. If the insulation is destroyed, a fault current may appear, flowing to the body of the input shield. Periodic sparking appears at the point of contact between the cable core and the housing. If the RCD did not stand at 100mA, then ignition is quite possible in the place of sparking, since dust contributes to this. Of course, this is a simplified example, but it is quite typical for understanding why a residual current device is needed.
Residual current device in the apartment
In apartments and houses, RCDs are installed to protect against electric shock, with a possible current leakage to the metal cases of household appliances, and also as additional protection against overcurrents. According to the regulations, RCDs with a cut-off current of at least 30 mA (preferably 10mA) are installed to protect the wiring groups of "wet areas" (bathroom, toilet). Any socket in the area of 2.40 m from the bath or pallet (electrical safety zone No. 3) must fall into a protected RCD. The same RCD should be installed on the electrical wiring of the children's room. For individual household appliances that come into contact with water (dishwasher, washing machine, etc.), an RCD with a cut-off current of 30mA is installed for protection, and each appliance has its own RCD.
The appearance of the RCD
By appearance RCD is a standard two-module (220 Volt) or four-module (380 Volt) device. 1 module is the size of a standard single-pole circuit breaker ().
Let's look at the RCD at 220 volts.
For connection, the RCD has 4 terminals, two at the top, two at the bottom. Where to supply power does not matter, but it is customary to connect power to the upper terminals, the tap from the lower terminals. One terminal is for connecting phase wire(left), the second for connecting the zero working wire (right). They are usually marked.
Note: in 380 volt four-pole RCDs, the zero working conductor terminal is located on the left.
