Before answering the question "Which RCD should be installed at the entrance to the apartment?" Let's figure out why install an RCD at all.

RCD is installed:

1. For the purposes of electrical safety - to protect against electric shock with direct or indirect contact;
2. In order to protect against fire in the event of leakage to the electrical enclosure or to the ground.

The principle of operation of the RCD

The principle of operation of the RCD is based on measuring the difference in currents in the phase (phase) conductors and the zero working conductor. In normal operation, the vector sum of the currents is zero. When a leakage occurs, the phase current differs from the current in the zero working conductor by the value of the leakage current. The current induced in the coil drives the core of the coil, which breaks the power circuit.

Requirements for the use of RCD

Requirements for the use of RCD for electrical safety purposes regulated by the PUE, chapters 1.7, 6.1, 7.1. The tripping current of an RCD installed for electrical safety purposes should not exceed 30 mA (use RCDs with a tripping current of 10 mA and 30 mA).

The rating of the RCD for the tripping current is selected in accordance with the requirements of clause 7.1.83 of the PUE. The total leakage current of the network in normal mode should not exceed 1/3 of the rated current of the RCD. Since there are no data on leakage currents, they are carried out in accordance with the requirements of this paragraph. When calculating, the leakage current of the electrical receiver is taken to be 0.4 mA for every 1 A of load current, and the network leakage current is 10 μA for each meter of cable length.

RCD installation requirements for fire protection regulated by the following documents:

1. PUE, p.7.1.84 “In order to increase the level of fire protection in case of short circuits to grounded parts, when the current is insufficient to operate the overcurrent protection, at the entrance to the apartment, individual house etc. it is recommended to install an RCD with a tripping current of up to 300 mA ";
2. Federal Law of July 22, 2008 N 123-FZ "Technical Regulations on Fire Safety Requirements". Article 82, part 4 “The power supply lines of the premises of buildings and structures must have protective shutdown devices that prevent the occurrence of a fire. Installation rules and parameters of residual current devices must take into account the fire safety requirements established in accordance with this Federal Law ".

In accordance with these requirements, an RCD with a trip current of 100 mA or 300 mA is installed at the entrance to the apartment. Such an RCD is called fire-fighting.

If the calculation shows that the apartment shield does not exceed 10 mA, then you can save money and you can install an RCD with a trip current of 30 mA at the entrance to the apartment. This RCD will serve as a "fire" RCD and RCD used for electrical safety purposes.

Otherwise, a “fire-fighting” RCD with a trip current of 100 mA or 300 mA is installed at the entrance to the apartment, and an RCD with a trip current of 10 mA or 30 mA is installed on the outgoing lines (where the installation of an RCD is required for electrical safety).

RCD is a residual current device. Currently, RCD is used almost everywhere, and in new buildings it is mandatory.

We install RCDs in apartment shields, in electrical panels of private houses. And that's right, of course. only RCD saves a person from electric shock. RCD also protects our apartment or a private house from fires that occur due to faults in the electrical wiring (poor contact, destruction of wire insulation). In my opinion, there can be only one answer to such a question as to install an RCD or not to install it - RCD must be installed in the electrical panel MANDATORY.

According to GOST 51326.1-99 "Automatic switches controlled by differential current for household and similar purposes without built-in overcurrent protection" automatic devices controlled by differential. current (RCD) have the abbreviation VDT(residual current switches). You can find this name of the RCD in the technical literature, in the name of the goods of online stores. In France, RCDs are designated ID (Schneider), in England - RCCD's.

The principle of operation of the RCD

The principle of operation of the RCD based on comparison of currents, which flow through the RCD, i.e. if in your own words - what amount of current passed through the RCDto consumers, the same amount of current should also come back from the RCD through the neutral conductor. In the picture, I 1 is the current in the RCD to the power receiver, I 2 is the current in the RCD from the power receiver. I 1 \u003d I 2 - this condition is met with high-quality electrical wiring or there is no interference in the operation of electrical wiring.

Suppose a person has touched some kind of conductor (phase or zero), in this case the person “takes away” part of the current I∆n, and there will be no equality between I 1 and I 2, because. I 1 > I 2 - I∆n. The RCD will feel this and turn off, thereby the RCD will save a person from possible death due to electric shock. The RCD must operate in 25-40 ms so that the current that will flow through the body does not increase to deadly.

RCD by number of phases

RCD are single-phase and three-phase. Here I think everything is clear, if a single-phase network, then the RCD is single-phase - it takes 2 modules (phase and zero). If a three-phase network, then the RCD is three-phase - it takes 4 modules (three phases and zero).

I note that in private houses, where recently three phases of 15 kW are connected, it is wrong to install a common three-phase RCD to protect a person from electric shock or fire safety, because. in the event of a current leakage in one of the phases, a three-phase RCD will disconnect all three phases. A three-phase RCD is installed on individual three-phase consumers, hobs (electric stoves), boilers in private homes.

RCD selection by rated current

Well-known manufacturers such as ABB and Schneider Electric produce modular RCDs, which are installed on a din rail, with rated currents of 16, 25, 40, 63 A. The rated current of the RCD shows the amount of current that the RCD can pass for as long as desired. Based on this line rated currents, and you should choose an RCD for an electrical panel in an apartment or a private house.

It's important to know that RCD does not have overcurrent protection(short-circuit currents, overload) and must therefore always be protected, rated current which is less than or equal to the rated current of the RCD - this is according to the rules. But I choose RCD differently, strictly one step above the machine .

I will explain why, the machine, as you know, passes current up to 1.13 of I nom. infinitely long, and in the range from 1.13-1.45 I nom. within 1 hour. Suppose we chose an automatic machine for 25A and an RCD also for 25A. As a result, for a whole hour, the RCD, which is designed for 25A, will pass a current of 25 * 1.45 = 36A, what will happen to the RCD in this case, I don’t know, but I think that RCD at 25A is highly likely to burn out.

The rated current of the RCD is indicated on its front.

There are RCDs for rated currents of both 32A and 50A, but these are Chinese RCDs, serious brands such as ABB, Schneider Electric or Legrand, RCDs of this rating are not produced.

Examples of how to choose the right RCD for rated current:

At the same time, remember that if "from above" the RCD is already protected by the machine, the value of which is less than the value of the RCD, then after this RCD you can connect machines, with a sum of ratings of at least 1000 A .

Rated breaking current RCD

Rated breaking current RCD I∆n(setpoint) is the current at which RCD is triggered(turns off). The RCD settings are 10 mA, 30 mA, 100 mA, 300 mA, 500 mA. It should be noted that non-release current when a person can no longer unclench his hands and discard the wire, is 30 mA and above. Therefore, to protect a person from electric shock, an RCD with a breaking current of 10 mA or 30 mA is chosen.

Rated RCD breaking current I∆n or leakage current is also indicated on the front panel of the RCD.

RCD 10 mA is used to protect electrical receivers in wet rooms or wet consumers, i.e. washing machines and dishwashers, sockets that are inside the bath or toilet, light in the bathroom, underfloor heating in the bathroom or toilet, light or sockets on balconies and loggias.

SP31-110-2003 p.A.4.15 For sanitary cabins, bathrooms and showers, it is recommended to install an RCD with a rated differential current up to 10 mA, if a separate line is selected on them, in other cases, for example when using one line for the bathroom, kitchen and corridor, use an RCD with a rated differential current up to 30 mA.

Those. An RCD with a setting of 10 mA is installed on a separate cable, to which only a washing machine is connected. But if from cable line other consumers are still powered, for example, corridor sockets, kitchens, then in this case an RCD with a trip current (setting) of 30 mA is installed.

RCD with a leakage current of 10 mA at ABB is released only at 16A. Schneider Electric and Hager have 25/10 mA and 16/10 mA RCDs in their product line.

RCD 30 mA installed on standard lines, i.e. ordinary household sockets, light in rooms, etc.

PUE p.7.1.79. In group networks supplying socket outlets, an RCD with a rated operating current should be used no more than 30 mA. It is allowed to connect several group lines to one RCD through separate circuit breakers(circuit breakers).

RCD 100, 300, 500 mA called fire-fighting, such RCDs will not save you from a fatal electric shock, but they will save an apartment or a private house from a fire due to faults in the wiring. Such an RCD for 100-500 mA is installed in the input shields, i.e. at the beginning of the line.

In the USA, RCDs with a rated breaking current of 6 mA are used, in Europe up to 30 mA.

It should be noted that RCD trips within the setting of 50-100%, i.e. if we have a 30 mA RCD, then it should turn off within 15-30 mA.

There are designers who promote double diffs. protection of "wet" consumers. This is when, for example, a washing machine is connected to a 16/10 mA RCD, which in turn is connected to a 40/30 mA group RCD.

In the end, what will we get? At the slightest "sneeze" of the washing machine, we turn off the entire group of machines (kitchen light, boiler and room light), because in most cases it is not known which RCD 25/30 mA or 16/10 mA will trip, or both will trip.

According to the set of rules for the design of electrical installations of residential and public buildings:

SP31-110-2003 A.4.2 When installing an RCD in series selectivity requirements must be met. With two- and multi-stage circuits, the RCD located closer to the power source should have tripping current settings and tripping time at least three times greater

But in fairness, it should be noted that if the electrical wiring is installed with high quality, then the RCDs do not work for years. Therefore, in this case, the last word belongs to the customer.

Types of RCDs according to the principle of operation

According to the principle of operation, RCDs are divided into electronic and electromechanical. Electronic RCDs are much cheaper than electromechanical RCDs. This is due to its lower reliability and low cost of production. The electronic RCD is “powered” by the network, and the operation of the electronic RCD depends on the parameters and quality of this very electrical network.

Let me give you an example, we have burnt out zero in floor plate, respectively, the power supply of the electronic RCD will be lost and it will not work. And if at this time a phase short circuit occurs on the body of the device, and a person touches it, then the electronic RCD will not work, because. it simply simply does not work, there is no power to the electronics due to a zero break. Or if, in a simple way, electronics is electronics, and Chinese electronics is doubly “electronics”, which can fail at any moment. Therefore, an electromechanical RCD, which does not depend on the state of the network, is much more reliable than an electronic RCD.

The principle of operation is based on the comparison of the incoming and outgoing current of the RCD of a conventional differential current transformer, and if the current is not equal to or greater than the setting (rated RCD breaking current in mA), as already mentioned above, then the RCD is turned off.

According to these schemes, it is possible to determine whether an electronic RCD or an electromechanical one, the schemes are applied to the RCD housings.

Well-known manufacturers such as ABB, Schneider Electric, Hager or Legrand do not produce electronic RCDs, only electromechanical RCDs. I put electromechanical RCDs in my electrical panels.

To compare the electronic and electromechanical RCDs, I offer a photo with their "insides". I would post an electronic RCD, some famous brand, not Chinese, but, as I wrote above, ABB, Schneider Electric, Legrand and other serious manufacturers do not produce electronic RCDs.

RCD types AC, A, B

Depending on the type, the RCD must be disconnected from different kind current leaks, there are RCDs that turn off only alternating current, there are RCDs that are alternating and pulsating current:

Responds to instantaneous alternating differential leakage current, i.e. these are ordinary consumers: lighting, underfloor heating, refrigerators, convectors, etc. The type of RCD AC is indicated on the panel, it is either the letters AC or a special symbol (pictogram) or both together.

Responds to both alternating and pulsating leakage current, which can slowly increase or occur suddenly. These are devices that use rectifiers and impulse blocks food: computers, washing machines, TVs, dishwashers, microwave ovens, i.e. where everything is controlled by electronics. In some instructions for modern electrical appliances, it is separately indicated that the installation of an RCD of type A is necessary. The pictogram for an RCD of type A is as follows

RCD type A is more expensive than RCD type AC, because "covers" a larger area of ​​protection. But it should be noted that the level of protection with RCDs of AC type is higher than if there were no RCDs at all.

PUE 7.1.78. In buildings, RCDs of type “A” can be used, responding to both alternating and pulsating fault currents, or “AC”, responding only to alternating leakage currents.
The sources of pulsating current are, for example, washing machines with speed controls, adjustable light sources, televisions, VCRs, personal computers, etc.

Often readers have a question: “Which RCD should I put on a refrigerator, washing machine, dishwasher, hob, etc.?”. The most correct answer, you will find in the instructions for household appliances.

But, for example, in Europe it is allowed to install RCDs only type A. RCDs type AC are prohibited.

RCD type B- a rarity in Russia, they are used in industry, where, in addition to other types of leaks, there are rectified current leaks, type B RCDs are not used in everyday life.

Trip delay (selectivity) RCD

According to the operating time delay, the RCD is divided into 3 types:

RCD without time delay, are used to protect a person from electric shock and from fires due to electrical wiring faults. RCD without time delay is installed on the line of electrical receivers. They are the first line of defense.

RCD type S (selective), also called fire fighting. This type S RCD operates with a delay (0.2-0.5 sec), so it does not protect a person, but only protects against fires. Fire RCD installed at the beginning of the line after the introductory machine and protects the input cable and the connection of automation in the shield, and is also the second stage of the differential. protection of the whole house from fire.

You can determine that this RCD is selective by the letter “S” on the panel, which means that the RCD is selective with a trip delay.

Examples a single-phase selective ABB fire protection RCD with a leakage current of 100 mA and a three-phase 300 mA fire protection RCD from Schneider Electric.

RCD type S is selected with a rated leakage current of 100-300 mA. A fire protection RCD with a setting of 100-300 mA is the second stage of protection, and according to the rules, if several RCDs are installed on the same line in the circuit, then each subsequent stage should be with a longer response time and current setting.

SP31-110-2003 A.4.2 When installing RCDs in series, selectivity requirements must be met. With two- and multi-stage RCD circuits located closer to the power source, must have settings tripping current and tripping time at least three times as large than the RCD located closer to the consumer.

If there were no time delay, and we have two RCDs on the line, one for 30 mA, the other for 100 mA, then with current leakage both RCDs would work and RCDs at 100 mA would de-energize the whole house. Therefore, in order not to run out into the street in shorts in the cold and turn on the fire protection RCD in the street shield, fire protection RCD is selected with a setting sufficient to prevent a fire.

RCD type G, the same as type S, only with a shorter time delay of 0.06-0.08 sec. RCDs are rare, and I had to wait 2-3 months for their “arrival”, which is very inconvenient for me, because. electrical panels freeze for a long time.

RCD connection diagram

Power (electricity) can be supplied to both the lower and upper contacts of the RCD - this statement applies to all leading manufacturers of electromechanical RCDs.

Example from the manual for RCD ABB F200

I share RCD connection diagrams for 2 types:

Connection diagram of a three-phase electric motor through an RCD

Often in the comments they ask about connecting three-phase motor(pump) through the RCD, the question arises due to the lack of three-phase electric motors neutral.

Actually, there is nothing complicated about this, for the correct operation of a three-phase RCD, we connect the neutral conductor to the zero terminal of the RCD from the supply side, and from the motor side it remains empty.

The RCD should be checked at least once a month. This is done quite simply, just click to the "TEST" button, which is on any RCD.

The RCD must turn off, this should be done with the load removed, when TVs, computers, a washing machine, etc. are turned off, so as not to once again “pull” sensitive equipment.

I like the ABB RCDs, which, like the ABB S200 series circuit breakers, have an indication of on (red) or off ( green color) positions.

Also, like the ABB S200 circuit breakers, there are two contacts on each pole at the top and bottom.

Thank you for your attention.

Quote with wrapping

Quote with wrapping

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 to the network in the event of a ground fault current.

Earth fault current occurs in wiring and/or electrical appliances when their insulation is broken for some reason, or when bare parts of wires that must be fixed in terminals, for example, inside household electrical appliances, touch the body of the devices - and the current begins to "leak" in an undesirable direction.

This can lead to a fire due to overheating (first the wiring or device, and then everything around) or to the fact that a person or a pet will suffer from the current - the consequences can be extremely unpleasant, even death. But this will happen only if you touch the conductor or the body of the equipment, which is energized.

The main difference between an RCD and a conventional circuit breaker is that it is designed specifically to break the earth fault current that the circuit breaker cannot detect. The RCD is able to turn it off in a fraction of a second, until the moment when it becomes dangerous to a person or property.

Where and how much to install

For one and two-room apartment- in the general 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 to protect against, as well as for separate lines supplying groups of electrical appliances with a metal case (washing and dishwasher, electric stove, refrigerator, and so on) - to protect against electric shock. If a malfunction occurs 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 of the RCD trip.

However, it must be borne in mind: neither RCDs nor conventional automata save from an electric arc, or an 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, sparks hidden from the eyes will occur, accompanied by an increase in ambient temperature and, as a result, ignition of flammable objects nearby: 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 an automaton, RCD and arc fault protection. On the English language such a device is called an arc fault detection device (AFDD), in Russia the name “arc fault protection device” (AFDD) is used.

An electrician can include the installation of such a device in the circuit if you tell him that you need an increased degree of protection. For example, for a children's room, where a child can handle wires inaccurately, or for groups of sockets for powerful electrical appliances with flexible wires prone to breakage.

It is equally important to install protection devices where the wiring is laid in an open way and it can be damaged. And also when planned, in order to avoid risks in case of accidental damage to hidden electrical wiring while drilling walls.

How to choose

A good electrician will recommend the manufacturer of the RCD and calculate the load, but you need to be sure that the recommendations are correct. And if you buy everything for repairs yourself, then all the more 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 better the components inside, the higher the price. For example, in some cheap devices there is no protection against burnout, and this can lead to ignition.

A cheap device can be made of brittle materials and break easily when you lift up the lever that has fallen when triggered. According to the RCD standard, it should be designed for 4,000 operations. This means that you will have to be puzzled by the choice only once, but only if you have purchased a quality product. By purchasing a low-quality device, you put yourself and loved ones at risk, not to mention material losses in case of 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, then the manufacturer has saved on the quality of internal components.

Conclusion

To resolve issues related to electricians in the house, it is advisable to involve professionals. However, the entire responsibility should not be shifted to their shoulders. It is better to be guided by the proverb "Trust, but verify." With even basic knowledge of the subject and an understanding of the scenario for the future use of electrical appliances in the house, you can save yourself and loved ones from problems with electricity.

In order to understand what household electrical equipment requires the installation of an RCD, let's look at the very purpose of this device and the principles of its operation.

RCD is a protective shutdown device against electric shock. In simple words, this is a special device that will de-energize an apartment, line or device in the event of a leakage current.

The principle of operation of the device is based on the constant monitoring and calculation of the incoming and outgoing conductor currents. If the parting notices changes (when normal operation these currents must be equal), it will turn off the power with lightning speed.

This device is designed to protect human life, so take its choice with all responsibility. After all, it is very important that the device is not only installed, but also of good quality, and at the right time it must work.

We repeat once again: the RCD does not protect the device from voltage surges, etc., but protects a person from electric shock. Therefore, the question of which devices to install protection and which not is not entirely true.

Install the RCD "on the apartment" (general), and then, if desired, on each room or even on separate equipment. Protection devices installed separately for each equipment will not protect better or worse.

The essence of individual installations is that when the RCD is triggered, not the whole house is disconnected from the power supply (if it is the only one installed “for the whole apartment”), but only a separate device or room.

Also, the RCD does not protect against static electricity (free electric charge on the surface or in the volume of dielectrics or on insulated conductors) - grounding must cope with this if it is done correctly. An ungrounded installation will not protect you from static electricity.

Connection and performance check

RCD is modular equipment, therefore it is installed in the switchboard along with other modular equipment. On each RCD, regardless of manufacturer, brand, model and power, there is a "Test" button.

After installation and connection, press the button - it will artificially create conditions, as with a leakage current, and turn off the equipment.

If this does not happen, look for errors in the wrong connection, or in the design of the RCD. It is worth checking the operation of the device once a year (at least).

How many RCDs to install

By installing one device on each equipment separately (refrigerator, washing machine, boiler) or for each line of outlets - ideal.

But if you have a limited budget, then instead of 10 cheap protection devices, it is better to buy 3-4 good and high-quality ones - common for the whole house, separately for the nursery, bathroom and kitchen.

This will be enough. Moreover, for each case you can choose and install an RCD with different characteristics.

Choice of protection by characteristics

Choosing an RCD for leakage current:

• 30mA for introductory RCD (for the whole house);
• 30mA for protection of socket groups;
• 10mA for a children's room, individual consumers (if installed separately on a washing machine, refrigerator), for a bathroom or rooms with high humidity.

Devices with a leakage current of 50 mA or more are not used to protect against human injury (the body will not withstand even 50 mA), but as fire protection.

Tripping characteristic (marked on each device):

• AC - devices that respond only to a sinusoidal (alternating) leakage current. Such RCDs are cheap, but less effective. The proof is that in European countries devices for protection with AC class are not used.
• A - reacting to leakage of alternating and direct current in devices with electronic converters. Universal look. Install for networks that power computers, washing machines and dishwashers, as the first type may not be effective for them. They cost a little more than AC.

One high-quality RCD is better than several low-quality ones - we have already talked about this above. Therefore, we recommend focusing on such manufacturers as:

• ABB - F200 series (type AC) and FH200 (type A), rated current 16-125 A, sensitivity 10, 30, 100, 300, 500mA, cable cross section up to 35 mm2.
• Eaton (Moeller) - PF4, PF6, PF7 and PFDM series (up to 63 A, maximum leakage current for fire protection 300mA, for protection against human injury 30mA).
• ETI - EFI6-2 series (up to 63 A, for protection against damage up to 30mA).
• Hager about 10 series (CDA CDS, FA, CD, etc.) with self-clamping terminals and without them, for one, two, three and four poles and the same number of contacts.

All presented models of RCDs are on sale in the online store of electrical engineering.

We thank the electrical company Axiom-Plus for their help in preparing the material.

Modern apartments and private houses are equipped with a large number of different household appliances. In this regard, the protection of people from electric shock comes to the fore. The main priority protective measures are the installation of traditional circuit breakers - circuit breakers and residual current devices - RCDs. However, in each specific case, in the presence of one or three-phase networks, technical questions appear, for example, RCD without grounding, does it work or not? In many old houses, there is no grounding, so the possibility of using protective devices in these conditions is of particular relevance.

Do I need grounding for RCD

Many homeowners believe that the protective device will only work correctly if there is a three-wire electrical circuit, with phase, zero and ground conductors. For the same reason, the question often arises, RCD or grounding, which is better. In order to give the correct answer, it is necessary to understand the purpose of each of them.

It is known that the main function of the RCD is to turn off the equipment when a current leakage occurs on the case. Thus, it is possible to avoid electric shock to a person. Grounding is installed for the same purpose, only it works according to a different scheme. When electricity appears on non-current-carrying parts, due to grounding, short circuit. As a result, the maximum current protection of the machine is activated and the equipment is de-energized.

Therefore, both methods of protection can be used separately, and if necessary, jointly, complementing each other. That's why mandatory installation earthing when using RCD is not required and the protective device can be used even in a two-wire single-phase network, in which there is no regular grounding. This conclusion is also confirmed by the design of the device itself, where there are phase and zero terminals, and there is no separate terminal for the ground wire. Particular attention should be paid to this, since grounding is mandatory installed only in houses of modern construction.

In old houses built back in the days of the USSR, they are still used two-wire networks, without earth conductor. In such cases, protective devices are especially needed. The whole difference in the operation of an RCD with and without grounding is only in the response time. In the presence of grounding, operation occurs almost instantly. RCD without grounding works only at the moment of touching the body of the device, which is energized. Therefore, the degree of protection is no longer as reliable as in the first option, but nevertheless, even in this case, the RCD protects against the unpleasant consequences of an electric shock.

How RCD with grounding works

The residual current device is selected in accordance with the network configuration where it is planned to be installed. You should immediately determine the presence or absence of a grounding conductor PE. In modern buildings, it is initially provided for by the project. At the sites of the old building, the PEN scheme is still used, which provides for the combination protective conductor with neutral wire.

Mounting the connection to the ground is considered more efficient, since the circuit is disconnected in this case, immediately when it appears. In the PEN scheme, as already noted, the shutdown occurs only after direct contact of a person with the equipment.

If there is still grounding in the circuit, then before installing the protective device, its type should be clarified. For example, the TN circuit assumes that the power supply neutral is solidly grounded. Its variety is, combining in a single wire the zero working and protective conductors in the entire electrical circuit. This simple and inexpensive option has a significant drawback: in the event of a break in the PEN conductor, if the device has its own ground, there is a danger that the entire potential will go to its case and the same voltage will appear on it as in the entire circuit.

Sometimes electricians use a jumper that shorts out the neutral and ground terminal in the outlet. Such a scheme is considered incorrect and dangerous due to the high probability of electric shock. When the PEN wire breaks, the RCD will not work, and a dangerous voltage will appear on the device case. Damage can only be avoided by accident: a person at the time of contact with a current-hazardous body must also touch the ground loop, for example, water pipes or heating pipes.

The TN-S circuit is considered the most reliable for connecting an RCD, where the connection of the neutral protective conductor is carried out separately. It is combined with the neutral only in the power source, which provides maximum protection and almost completely eliminates the possibility of electric shock. Even if the neutral or ground wire breaks, all devices in the circuit will continue to work. Dangerous voltage will not appear on the housings, since the potential will transfer to another, the remaining wire. With two wires at once, all devices and the circuit itself will not pose a danger to people, since the electricity will be completely turned off.

There is another so-called intermediate TN-C-S connection scheme, when the neutral and ground wires can only be combined in separate sections and acquire the properties of a PEN conductor. In this case, the installation of an RCD is mandatory, otherwise the circuit will be left without protection at all.

Will an RCD work without grounding

The operation of the protective device in a two-wire network occurs in special conditions. Therefore, many owners have a question, will the RCD work without grounding and will it provide protection against electric shock? In order to get an answer, it is necessary to trace the entire triggering mechanism. When a breakdown occurs on the equipment case, the RCD will not immediately trip, since there is no grounding and there is no way for current leakage to pass further. At the same time, a potential is formed on the body of the device that is dangerous to human health and life.

At the moment of touching the housing, the current leakage path to earth will pass through the human body. After a certain period of time, the current value will become equal to the threshold of the RCD, and only then will a shutdown occur with the cessation of the current supply to the faulty device. The amount of time a person is exposed to the current will depend on the pickup setting of the protective device. Despite the fairly quick shutdown, this is quite enough to cause a serious electrical injury. In the presence of grounding, the RCD would work immediately after a current leakage and would turn off the device even before a person came into contact with it.

Thus, an RCD without grounding can be connected, however, such a circuit does not guarantee 100% safety. However, two-wire networks are still used in older houses, and their conversion to more modern three-wire networks is not always possible from a technical point of view. Therefore, in many cases, RCD is the only option to protect people and household appliances. When used together with residual current devices, circuit breakers must be installed to disconnect the network in case of overloads and short circuits.

How to connect an RCD in an apartment without grounding - Scheme No. 1

The only protective device is installed at the entrance and covers all the wiring in the apartment. The power supply is supplied to the switchboard through input cable. Then it goes to a two-pole machine, and then to the RCD. After that, the machines are installed on the outgoing lines.

A significant advantage is the low cost of such a circuit due to the use of only one protective device. All devices can be compactly placed even in a small switchboard. But, a significant drawback of such a shutdown will be the operation of the RCD during current leakage, as a result of which the entire apartment will be de-energized.

Scheme No. 2

The operation of an RCD without grounding can be carried out according to one more scheme. In this case, protective devices are installed not only at the inlet, but also at each outgoing branch. The introductory RCD is mounted in the same way as in the previous version, and all the rest are installed after the machines that protect the outgoing lines. The total number of security devices will depend on the specific home network configuration. Often, water heaters, electric stoves, dishwashers and washing machines are separately connected to the protection.

Thus, in case of current leakage on any line, the RCD installed on this line will trip. That is, in all other parts of the apartment, the voltage will not disappear, and the rest of the equipment will continue to work. The only drawback of this scheme is the large size of the switchboard, which is necessary to accommodate a large number of RCDs and automata. In addition, the protective devices themselves are not cheap.

Often the question arises of the need to install an introductory RCD if each line is protected. The fact is that the outgoing protective device may, for one reason or another, not work with current leakage. In this case, the introductory RCD serves as insurance and through certain time turn off the entire network.

RCD in TN-C system

Very often there are questions about the possibility of connecting an RCD in the TN-C grounding system and its effectiveness. Variants of this system can be three-phase with four wires or single-phase with two wires. In the first case, the wires consist of three phase and one zero, and in the second - of two phase and zero conductors.

Most experts unconditionally recommend the installation of protective devices in such systems, since they are the ones that work with current leakage that is dangerous to humans. However, there is a so-called "opposition", according to which the installation of an RCD in TN-C system not only ineffective, but also dangerous. This is due to the fact that the protection works only with direct contact with live parts, and not in advance, with the appearance of a leakage current. In addition, in houses with old wiring, such devices will turn off for no apparent reason.

Most electricians and apartment owners are still in favor of installing an RCD. In any case, it will not be useless and will work at the right time, saving health or even life itself. Protective device significantly increases electrical safety and makes the life of living people more peaceful.