Hello Dear reader of the site site. Today we’ll talk about RCDs for protecting people from leakage currents (device protective shutdown). RCD protection is installed in electrical networks to protect people from leakage currents and prevent fires.
Purpose
RCD is electrical device specially designed to disconnect power electrical appliances with 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 are turned off electrical network in case 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 (amps)
- 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.
- It is better to install in apartments and houses RCD 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 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.
Regulatory documents
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.
In order to protect the electrical network of a house or apartment, circuit breakers or fuses. These elements help prevent fire during short circuit, but are completely unable to protect against electric shock. A product for protective shutdown of electricity, the operating principle of which is aimed at preventing current leakage to the device body, allows you to instantly de-energize the entire home network if the phase current is outside the “permitted” 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 to 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 the electrical wiring lacks a third protective conductor, which should contain grounding. With such a wiring diagram, powerful devices, the “ground” of which is connected to the grounding terminal of the socket, are not protected, and if phase current leaks to the housing, 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 general network.
As a rule, the effect of current when a person touches the body of the device in this case will be a negligible amount of 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 a “breakdown” occurs on the housing.
Why you need an RCD in an apartment is now clear, but why use this device for a private household?
RCD in a private house
Many private developers do not understand why an RCD is needed in a house, because such a facility can be easily equipped with high-quality grounding, which will ensure the “disposal” of dangerous voltage from the body of any electrical appliance. So why do you need a residual current device in a private home?
Connecting a high-quality grounding conductor allows you to protect a person from severe electrical injuries when touching the housing 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 internal conductors from this effect, it is necessary to unplug all devices equipped with a grounding wire from the outlet after use, or you need to install an RCD in the circuit of the electrical device. Next we will talk about why to install a protective device in the bathroom.
RCD in the bathroom
You should also install a device to protect against electric shock in your bathroom. 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 do you need to install a safety device in the bathroom?
To maximize the effectiveness of such a safety mechanism, you should choose a model whose sensitivity is no more than 30 mA. If powerful appliances are not connected in the bathroom, then the ideal option for a room with high humidity would be to install a protective product with a leakage current of 10 mA. Such devices will cost much more, but their use will maximize the safety of people from exposure to electricity. Why you need it is easy to understand, but why install protection on lighting fixtures?
RCD for lighting
RCDs for lighting also need to be installed according to all the rules. Why this needs to be done will be discussed below. Even in the case when the phase wire was passed through the switch, it is necessary to install a protective product on the entire circuit of the lighting device, because an emergency power outage may be necessary if non-standard work lamp
For example, a heavy chandelier may come off and, along with the light bulbs that are on, fall on people. At this moment, a power outage is guaranteed to occur if there is a leak. Will protect the product from electric shock and in damp rooms with low ceilings.
For example, in a damp basement it is necessary 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 wet insulation of a conductor or lamp socket.
It is also necessary to equip all street lamps with a protective device, because the operation of such products occurs in very unfavorable conditions of heat, high humidity or low temperatures, in winter time. Despite the increased protection of outdoor lamps from moisture, over time from mechanical damage or for other reasons, the insulating layer and the metal surface can become significantly thinner
lighting fixture will be exposed to 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 three-phase network
All equipment operating from a three-phase network must also be connected to a protective power shutdown system. The magnitude of the leakage current in such networks can be too high, so these products do not protect a person from electric shock, but they allow you to disconnect electricity consumers when a phase breakdown occurs on the “ground” of the device. In this way, it is possible to completely eliminate the possibility of dangerous electrical potential appearing on the device body. This connection diagram can only be connected if there is a protective ground in the wiring of the 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 the RCD
The residual current shutdown system must be installed in such a way that the power of the devices connected to the electrical network is not higher than the maximum permissible for a given RCD model, for which purpose, before carrying out installation work You should study the instructions for the protective device.
For better quality and reliable protection home electrical wiring, you need to install one device of higher power in the panel, 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 casing, then installation work can be carried out in close proximity to the protected object. In this case, the most suitable model There will be a protective product that has a built-in circuit breaker. Installation of such an RCD allows not only to ensure a minimum probability of electric shock, but also to protect the electrical circuit from short circuits.
Why do you need to install an RCD in an electrical circuit, and why do this in accordance with the safety regulations and operating instructions 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 related to electricity, but also for ordinary users of household appliances.
Usually, many home craftsmen no longer care about the question: “Why do you need to install a protective device” after they feel the effects of electric current with a voltage of 220 V. Why this needs to be done according to the rules, when selecting a protective device based on power, is also often found out through a process of 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.
PUE 7 - Rules for the construction of electrical installations, Section 7 ELECTRICAL EQUIPMENT OF SPECIAL INSTALLATIONS, in this case we will limit ourselves to excerpts from the Rules for RCD and Refrigeration Protection:
7.1.21. When supplying single-phase consumers of buildings from a multiphase distribution network allowed for different groups of single-phase consumers to have common N and PE conductors (five-wire network), laid directly from the ASU, combining N and PE conductors (four-wire network with PEN conductor) not allowed . When supplying single-phase consumers from a multiphase supply network with branches from overhead lines, when the PEN conductor of the overhead line is common to groups of single-phase consumers powered from different phases, recommended provide for protective shutdown of consumers when the voltage exceeds the permissible limit, arising due to load asymmetry when the PEN conductor breaks. Shutdown should be carried out at the entrance to the building, for example by influencing the independent release of the input circuit breaker via an overvoltage relay, while should both phase (L) and neutral working (N) conductors are disconnected. When choosing devices and instruments installed at the input, preference, all other things being equal, should be given to devices and instruments that remain operational when the voltage exceeds the permissible limit, arising due to load asymmetry when the PEN or N conductor breaks, while their switching and other operating characteristics may not be fulfilled . In all cases, in circuits of PE and PEN conductors prohibited have switching contact and non-contact elements. Allowed connections that can be disassembled using a tool, as well as connectors specially designed for this purpose.
INPUT DEVICES, DISTRIBUTION BOARDS, DISTRIBUTION POINTS, GROUP BOARDS
7.1.22. A VU or ASU must be installed at the entrance to the building. One or more VU or ASU may be installed in a building. If there are several economically separate consumers in a building, it is recommended that each of them install an independent VU or ASU.
The ASU is also allowed to supply power to consumers located in other buildings, provided that these consumers are functionally connected. For branches from overhead lines with a rated current of up to 25 A, the VU or ASU may not be installed at the inputs to the building if the distance from the branch to the group panel, which in this case performs the functions of the VU, is no more than 3 m. This section of the network must be flexible copper cable with a conductor cross-section of at least 4 mm 2, flame retardant, laid in steel pipe, in this case, the requirements for ensuring a reliable contact connection with the branch wires must be met. With air input should install surge suppressors.
INTERNAL ELECTRICAL EQUIPMENT
7.1.47. In bathrooms, showers and lavatories, only electrical equipment should be used that is specifically designed for installation in the relevant areas of these premises in accordance with GOST R 50571.11-96 “Electrical installations of buildings. Part 7. Requirements for special electrical installations. Section 701 - Bathrooms and Shower Facilities" and the following requirements must be met:
- electrical equipment must have a degree of protection against water not lower than:
in zone 0 - 1РХ7;
in zone 1 - 1РХ5;
in zone 2 - 1РХ4 (1РХ5 in public baths);
in zone 3 - 1РХ1 (1РХ5 in public baths);
- in zone 0, electrical appliances with voltages up to 12 V, intended for use in the bath, can be used, and the power source must be located outside this zone;
- in zone 1 only water heaters can be installed;
- in zone 2 water heaters and lamps of protection class 2 can be installed;
- in zones 0, 1 and 2, the installation of junction boxes, switchgear and control devices is not allowed.
7.1.48. Installation of plug sockets in bathrooms, showers, soap rooms of baths, rooms containing heaters for saunas (hereinafter referred to as “saunas”), as well as in washing rooms of laundries is not allowed, with the exception of bathrooms in apartments and hotel rooms.
In the bathrooms of apartments and hotel rooms installation of plug sockets in zone 3 is allowed according to GOST R 50571.11-96, connected to the network through isolation transformers or protected by a residual current device that responds to a differential current not exceeding 30 mA.
Any switches and sockets must be located at a distance of at least 0.6 m from the doorway of the shower stall.
PROTECTIVE SAFETY MEASURES
7.1.71. To protect group lines supplying socket outlets for portable electrical appliances, recommended provide residual current devices (RCDs)).
7.1.72. If the overcurrent protection device (circuit breaker, fuse) does not provide an automatic shutdown time of 0.4 s at a rated voltage of 220 V due to low values of short circuit currents and the installation (apartment) is not covered by the potential equalization system, installation of an RCD is mandatory .
7.1.73. When installing an RCD in series should selectivity requirements are met. With two- and multi-stage circuits, the RCD located closer to the power source must have a setting and response time that is at least 3 times greater than that of the RCD located closer to the consumer.
7.1.74.In the coverage area of the RCD, the neutral working conductor shouldn't have connections with grounded elements and a neutral protective conductor.
7.1.75. In all cases of using RCD should ensure reliable switching of load circuits, taking into account possible overloads.
Not allowed 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, necessary their calculation check in overcurrent modes, taking into account the protective characteristics of the superior device that provides overcurrent protection.
7.1.77. In residential buildings not allowed apply RCD, automatically disconnecting the consumer from the network in the event of a loss or unacceptable drop in network voltage. At the same time, the RCD should remain operational for a period of at least 5 s when the voltage drops to 50% of the nominal voltage.
7.1.78. In buildings can use RCDs of type “A”, which respond to both alternating and pulsating fault currents, or “AC”, which respond 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.
7.1.79. In group networks feeding plug sockets, should apply RCD with a rated operating current of no more than 30 mA.
Allowed connection to one RCD several group lines through separate circuit breakers (fuses).
RCD installation in lines feeding stationary equipment and lamps, as well as in general lighting networks, as a rule, not required .
7.1.81. RCD installation prohibited for electrical receivers, the disconnection of which can lead to situations dangerous for consumers (disabling fire alarms, etc.).
7.1.82. Mandatory is the installation of an RCD with a rated response current of no more than 30 mA for group lines supplying outlet networks located outdoors and in especially dangerous and high-risk areas, for example in zone 3 of bathrooms and shower rooms in apartments and hotel rooms.
7.1.83. Total network leakage current, taking into account connected stationary and portable power receivers in normal operation shouldn't 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.
7.1.84. To increase the level of fire protection in case of short circuits to grounded parts, when the current value is insufficient to trigger the maximum current protection, at the entrance to an apartment, individual house, etc. recommended RCD installation with operating current up to 300 mA.
7.1.85. For residential buildings, if the requirements of clause 7.1.83 are met, the functions RCD according to paragraphs. 7.1.79 and 7.1.84 can be performed by one device with an operating current of no more than 30 mA.
7.1.86. If the RCD is intended for protection against electric shock and fire or only for protection against fire, then it should disconnect both the phase and neutral working conductors; overcurrent protection in the neutral working conductor is not required.
7.1.88. All open conductive parts of stationary electrical installations, third-party conductive parts and neutral protective conductors of all electrical equipment (including plug sockets) must be connected to the additional potential equalization system.
For bathrooms and shower rooms, an additional potential equalization system is mandatory and must include, among other things, the connection of third-party conductive parts extending outside the premises. If there is no electrical equipment with neutral protective conductors connected to the potential equalization system, then the potential equalization system should be connected to the PE bus (clamp) at the input. Heating elements embedded in the floor must be covered with grounded metal mesh or a grounded metal shell connected to a potential equalization system. As additional protection For heating elements, it is recommended to use an RCD with a current of up to 30 mA.
It is not allowed to use local potential equalization systems for saunas, baths and shower rooms.
I repeat once again that only excerpts from the Rules are given here, anyone who wishes can read them in full on the Internet (PUE 7 - Rules for the construction of electrical installations, Section 7), in this article I am not going to comment on these Rules, although I agree that there are controversial questions and also comments on them in RuNet.
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There comes a time in almost every person’s life when he begins to think about ensuring proper housing, health and life. But in order to protect yourself and your own home, you need to approach the decision as consciously as possible. this issue. We must pay attention special attention electrical wiring in the house, because safety largely depends on it. You need to be very careful when choosing wiring. You can't make hasty decisions in this matter.
Currently, almost every apartment and house uses a huge variety of household electrical appliances. The greater its quantity, the more significant the load on the electrical cable will be.
If you do not use special protection devices, there is a possibility of unpleasant problems. Almost every material can become unusable over time. The same can be said about external wiring, internal wire, which is located directly in the body of the electrical device. Over time, the insulating properties are gradually lost. Therefore, electricity leaks may appear, which in turn acts as a direct threat to human life. It is important to avoid these types of problems. To do this, you just need to start using special protective devices. One of the main devices of this type, which has recently become increasingly popular, is an RCD, that is, a residual current device.
Why do you need to install an RCD in your apartment?
It is not very difficult to understand from the name of the device that it was created to provide the appropriate level of protection to every living creature so that it is not affected by electric current. It also allows you to effectively prevent the possibility of electrical wiring fires as a result of overheating, as well as various malfunctions.
It was previously noted that a violation of the integrity of the internal electrical circuit of the devices may well occur. There are several main reasons this fact, among which we can note thermal damage, mechanical impact, as well as basic aging of electrical wiring insulation. Time spares nothing and wiring is no exception to the general rules.
If there is no protective shutdown device, then almost each of the reasons described above can cause harm to a person. There is a possibility of losing not only your own home due to fire, but there is also a certain risk of death under voltage. An electrical shock may well provoke cardiac fibrillation. And if there is no one nearby who can come to the rescue, this threatens with extremely significant consequences.
Of course, in this case, a person’s own resistance also plays a significant role. The higher it is, the less chance you will have of staying alive. There is hardly any need for such a risk to your health. It is better to protect yourself and everyone living in the house or apartment from such potential damage. To do this, you just need to install a protection device in your home. You should not skimp, because it is a kind of guarantee of health and safety from electric shock.
You can give a specific example. When the washing machine is running and the insulation on the phase wire is damaged. This all applies to the body. As a result, the latter finds itself under a certain tension. If a person stands on a wet floor and accidentally touches a metal part washing machine, then a circuit is formed and the current will pass through the person, going into the ground. The RCD will understand that something is wrong here, that not all the current has returned, and will turn off the voltage almost instantly. This will save a person’s life. Of course, the person will probably feel some discomfort, such as a slight tingling sensation, but will remain alive.
How does an RCD work?
The key purpose of this device is to protect people from damaged equipment, parts of which may have dangerous potential. The phase and zero from the direct power source are connected to the upper terminals of the device, and the zero and phase going to the load are connected to the lower terminals. In this case electric current flows from the power source, passing to the device through the RCD, after which it returns to the network through the RCD. We can conclude from this that the RCD is a kind of controller that monitors the current strength at the “input” and “output”. Then, when the indicators at the input and output of the device are different, then there is a leak somewhere. The protective shutdown device reacts to such a leak extremely quickly. Typically, it takes about 0.04 seconds to operate and turn off.
In an adequately functioning electrical network, there should be no significant difference between the incoming and outgoing currents. If the amount of current that goes in and out is the same, then no tripping will occur. However, in the event that the current finds another way to exit, the RCD will necessarily turn off, stopping the power supply.
We must also not forget that the device can significantly increase the level of safety electrical installations, however, is not able to eliminate the risk of electrical damage or fire. The device cannot respond to emergency situations when no current leakage occurs. For example, it could be a short circuit or an overload. The device will not be able to respond to them.
To protect a person from electric shock, a device is used whose normal current values vary from 10 to 30 mA. This is due to the fact that a higher current can be lethal to the human body.
Currently, manufacturers produce RCDs with leakage current ratings of 100, 300 and 500 mA. Everyone probably knows that with a current of 50 mA, a person will not be able to free himself from the wire without the help of others. And if the value reaches 80 mA, then instant death will follow. In reality, an RCD is not used to provide normal protection against electric shock. It should perform a slightly different task.
The need to use a device with a rating of 100 mA or more is due to the fact that almost any electrical power system contains so-called “stray” currents. That is, there is a leakage of natural currents. Almost nowhere is there perfect insulation, which is why there is usually a natural leakage of current.
Residual shutdown devices, which are designed for leakage rates of 300 mA, make it possible to eliminate the possibility of a fire. For example, in the case of a long-term leakage of current with parameters from 200 to 500 mA, a significant amount of thermal energy will be released, which may be quite enough to ignite nearby materials.
For this reason, RCDs are primarily used to guarantee fire protection. A device with this rating allows you to provide a reserve of the main RCDs. They are usually installed at the entrance to the room.
The fact that in modern houses and apartments it is necessary to install protective shutdown devices has already been said more than once. Their main goal is to protect human life from the effects of electric current. But is it always possible to carry out installation, given that the network can be different - three-phase and single-phase, with and without a grounding protective conductor. Let's talk about how to connect an RCD without grounding. The scheme by which these devices are connected is not complicated. If you do all the apartment wiring yourself, you can easily handle installing an RCD. But the best decision would be to entrust this work to professionals.
Before talking about how to connect an RCD without grounding, you need to have a clear understanding of the types of electrical household networks.
Types of electrical networks
The power supply to our apartments and houses comes from a single-phase or three-phase network.
Single-phase electrical power is one phase and zero. For food household appliances And lighting fixtures need to phase voltage, which is obtained at the output after the step-down transformer. This single-phase power supply involves powering from one phase of the line.
Electric current moves through the phase conductor, and through the neutral conductor it returns to the ground. Most often, this type of electrical wiring is used in an apartment, and it has two varieties:
- Single-phase two-wire network (without ground). This type of electrical network can most often be found in old houses; it does not provide for grounding of electrical appliances. The circuit includes only a neutral wire, marked N, and one phase conductor, which is designated L.
- Single-phase three-wire network. In addition to the neutral and phase conductors, it also contains a protective grounding conductor, designated PE. The housings of electrical devices must be connected to grounding conductors; this will protect the equipment itself from burnout, and people from the action of electric current.
There is often equipment in the house that needs three-phase voltage(pumps, engines, if there are machines in the barn or garage). In this case, the network will consist of neutral and three phase wires (L1, L2, L3).
Likewise three-phase network There are four-wire versions and five-wire versions (when there is also a protective grounding conductor).
We have decided on the types of networks, and now we will move directly to the question: is it possible to connect an RCD without grounding and how to properly install this device?
Is it possible to connect an RCD without grounding - on video:
Why is it necessary to install an RCD?
Let's consider this question at simple example. Let's say there is a washing machine in the bathroom. Electrical wiring in the apartment is made only with neutral and phase wires, there is no protective grounding, and the RCD is not installed.
Let us present the situation further. The insulating layer inside the machine was damaged, causing the phase to come into contact with the metal body. Some potential has appeared, that is, the body of the washing machine is now energized. If a person approaches it and touches it, it will play the role of a conductor through which electric current will flow. The effect of the current will continue until the person withdraws his hand from the washing machine, because the damaged area will not be turned off by any device. Unfortunately, under the influence of current, a person’s muscles are paralyzed, and it is not always possible to pull the hand away.
There are two options here - either the person loses consciousness and gives in, or someone else helps him by turning off the input machine for the room.
If, in the example considered, there was an RCD in the distribution panel, it would react to the appearance of a leakage current, turn off and protect human life. It is for this reason that in an apartment equipped with a large number of powerful household appliances, the installation of an RCD is simply necessary.
How does an RCD work with and without grounding?
By what principle does an RCD work in a two-wire network if there is no grounding? When an insulating breakdown occurs on the device body, the residual current device will not work, because the body is not grounded and there is no path for the current leakage to pass through. In this case, the device body will be dangerous for human life potential.
The moment a person touches the body of the device, the current leakage will go to the ground through his body. When the magnitude of this current is equal to the RCD response threshold, a shutdown will occur, and voltage from the supply network will not be supplied to the damaged electrical appliance.
How long a person will be under the influence of a current leak depends on the RCD trigger setting.
Although it will shut down quickly, this may be enough time to cause serious electrical injury.
But if the housing was connected to protective grounding, the RCD would react and turn off immediately as soon as an insulation breakdown occurred.
As you can see, the RCD connection diagram without grounding is actually applicable, but does not provide a 100% guarantee of safety. But since in old houses there is mainly a two-wire electrical network, and converting it to a three-wire one is not so easy, the only way out to protect equipment and people is to install an RCD.
Visual operating principle of an RCD without grounding in the video:
The operating principle of this device is based on measuring processes. The current value at the input and output is recorded. If these readings are the same, then there is no reason to trigger. As soon as a current leak appears in the network, the output value will become smaller and the device will turn off the damaged area. The RCD operates due to a tripping mechanism in conjunction with an electromagnetic relay.
Scheme options
Before connecting an RCD without grounding, remember an important tip! The circuit must include, in addition to residual current devices, ordinary circuit breakers.
Many naively believe that these are the same mechanisms and serve the same purpose. The main thing is to understand the difference in their work. The circuit breaker is a protection for the supply voltage network. It turns off the damaged section if overcurrents arise in it as a result of a short circuit or overload. Due to this emergency does not apply to the general network, and it remains in good condition.
The RCD only protects against current leaks; their values are very small compared to short-circuit currents. Therefore, if a short circuit or overload occurs in the network and there is no circuit breaker, the RCD will not respond. It should always be installed in a circuit paired with a circuit breaker.
Connecting an RCD without grounding can be done in two ways.
Input connection
With this scheme, one RCD is installed to simultaneously protect all residential wiring.
Voltage flows from the network through the input cable to the distribution panel and goes to the two-pole circuit breaker. Then a residual current device is installed in the circuit. Next, automatic outgoing connections are installed. All these outgoing consumers are simultaneously protected by one RCD installed at the entrance.
The advantage of this scheme is that only one residual current device is used, therefore significant material costs are not required. In addition, everything can be compactly placed in the distribution panel and it will not be large.
But there is also a significant drawback. Imagine that some household appliance is currently connected to an outlet and a phase is shorted to the metal housing. The RCD reacts to the current leakage and turns off. The power supply to the entire apartment is stopped. If at that moment only one electrical appliance was connected to the outlet, it is not difficult to look for damage. What if a lot of household appliances were working at the same time? Not only did the refrigerator stop working immediately when the power supply stopped, the air conditioner froze, the program stopped washing machine or bread maker, there are unsaved documents on the computer. So it will still be necessary to find which specific technique the phase was closed on, and this already causes certain difficulties.
Therefore, before choosing this RCD connection scheme, think about the convenience of its further operation.
Connection at the input and outgoing branches
This version of the circuit involves connecting several RCDs. One, as discussed above, is mounted after the introductory machine at the entrance. The rest are placed behind the circuit breakers of outgoing connections. How many there will be depends on how you group your home electrical network. Perhaps you will have one machine and RCD for each separate room. There is an option to separate socket and lighting consumer groups. In some schemes, separate protection is provided for the boiler, washing or dishwasher, air conditioner or electric furnace.
How does such a scheme work? For example, a current leak occurred on one of the outgoing lines. An RCD protecting this particular line will be triggered. The tension in the entire apartment does not disappear, all other equipment remains in working order. This is the undoubted advantage of this version of the scheme. Its disadvantage is that the distribution panel will be of impressive size, and it is not very convenient to place it in it large number RCD and automatic devices. And it won’t be cheap in material terms.
The question arises, why is there another RCD at the input in the circuit? There are situations when, for one reason or another, the outgoing device did not respond to the current leakage. In this case, the input RCD will be a safety net; after a certain period of time it will turn off. In principle, it can be omitted and the circuit can be completed without an input device. But if your financial capabilities allow, it is better to insure yourself, after all, we are talking about people’s safety.
Clearly general principle RCD connections in the following video:
Circuit assembly
There are no difficulties in practical implementation. The entire algorithm will look like this:
- All work with electricity always begins with de-energizing the workplace. Therefore, turn off the apartment input machine. With the help indicator screwdriver make sure that there is really no voltage at its output.
- Attach the residual current device to the DIN rail. On the back side there are latches that must be inserted into the perforated holes on the rail.
- The body of the residual current device is marked with input and output contacts for neutral and phase conductors. Power is supplied to the RCD from above, and the load is connected from below. From the output terminal of the circuit breaker, connect the phase conductor “L” to the corresponding input terminal of the RCD. Make similar connections with the neutral wire “N”.
- Distribute the phase output from the RCD among all outgoing line machines.
- Connect the output from the zero contact to the zero bus. And from there the conductors will disperse to consumers. After the RCD, the neutral conductors are not combined into one node; this will cause false alarms of the device.
- After completing all switching, turn on the input machine. Check the correct connection and operation of the residual current device. For this purpose, there is a special “TEST” button on the RCD body. Its main goal is to simulate current leakage. From the phase conductor, current is supplied to the resistance, and from it, bypassing the transformer, to the neutral conductor. Due to the resistance, the current at the output has become less and, due to the resulting imbalance, the shutdown mechanism will operate. Press the test button, the RCD should turn off. If this does not happen, it means that there are inaccuracies in the connection or the device is not working properly.
Common mistakes when connecting an RCD on video:
If you connect an RCD with grounding, remember what to use for this purpose water pipes or other communication structures are unacceptable.
Grounding must be done correctly, and not done independently, only in this case can you be completely confident in safety. If the grounding is not working, be sure to disconnect and insulate the conductors coming into the electrical panel.