How to choose an RCD for an apartment and a private house: an analysis of the main characteristics of the device

Protection options for a single-phase network

Manufacturers of powerful household appliances mention the need to install a set of protective devices. Often, the accompanying documentation for a washing machine, electric stove, dishwasher or boiler indicates which devices need to be additionally installed in the network.

However, more and more often several devices are used - for separate circuits or groups.In this case, the device in conjunction with the machine (s) is mounted in a panel and connected to a certain line

Considering the number of different circuits serving sockets, switches, equipment that loads the network to the maximum, we can say that there are an infinite number of RCD connection schemes. In domestic conditions, you can even install a socket with a built-in RCD.

Next, consider the popular connection options, which are the main ones.

Option #1 - common RCD for 1-phase network.

The place of the RCD is at the entrance of the power line to the apartment (house). It is installed between a common 2-pole machine and a set of machines for servicing various power lines - lighting and socket circuits, separate branches for household appliances, etc.

If a leakage current occurs on any of the outgoing electrical circuits, the protective device will immediately turn off all lines. This, of course, is its minus, since it will not be possible to determine exactly where the malfunction is.

Suppose that a current leakage has occurred due to the contact of a phase wire with a metal device connected to the network. The RCD trips, the voltage in the system disappears, and it will be quite difficult to find the cause of the shutdown.

The positive side concerns savings: one device costs less, and it takes up less space in the electrical panel.

Option #2 - common RCD for 1-phase network + meter.

A distinctive feature of the scheme is the presence of an electricity meter, the installation of which is mandatory.

Current leakage protection is also connected to the machines, but a meter is connected to it on the incoming line.

If it is necessary to cut off the power supply to an apartment or house, they turn off the general machine, and not the RCD, although they are installed side by side and serve the same network

The advantages of this arrangement are the same as those of the previous solution - saving space on the electrical panel and money. The disadvantage is the difficulty of detecting the place of current leakage.

Option #3 - common RCD for 1-phase network + group RCD.

The scheme is one of the more complicated varieties of the previous version.

Thanks to the installation of additional devices for each working circuit, protection against leakage currents becomes double. From a security point of view, this is a great option.

Suppose an emergency current leakage occurred, and the connected RCD of the lighting circuit for some reason did not work. Then the common device reacts and disconnects all lines

So that both devices (private and common) do not immediately work, it is necessary to observe selectivity, that is, when installing, take into account both the response time and the current characteristics of the devices.

The positive side of the scheme is that in an emergency one circuit will turn off. It is extremely rare that the entire network goes down.

This can happen if the RCD installed on a particular line:

• defective;
• out of order;
• does not match the load.

To avoid such situations, we recommend that you familiarize yourself with the methods for checking the RCD for performance.

Cons - the workload of the electrical panel with a lot of the same type of devices and additional expenses.

Option #4 - 1-phase network + group RCDs.

Practice has shown that the circuit without installing a common RCD also functions well.

Of course, there is no insurance against the failure of one protection, but this can be easily fixed by purchasing a more expensive device from a manufacturer you can trust.

The scheme resembles a variant with general protection, but without installing an RCD for each individual group.It has an important positive point - it is easier to determine the source of the leak here

From the point of view of economy, the wiring of several devices loses - one common one would cost much less.

If the electrical network in your apartment is not grounded, we recommend that you familiarize yourself with the diagrams RCD connection without grounding.

The importance of acquiring a quality RCD

An irresponsible approach to choosing a residual current device, that is, buying a device that does not fit the house or apartment according to its characteristics, can cause some problems:

• false triggering of automation, since small leakages of electric current are a natural situation for wiring that was installed relatively long ago;
• untimely receipt of information about a dangerous incident if an overly powerful RCD is selected, which can lead to electric shock;
• the inability of the RCD to function with the existing wiring from aluminum conductors, because almost all devices work only on copper wires.

In order not to make a mistake when choosing an RCD, it does not hurt to carefully read the parameters of the device before buying.

Table: main parameters of the RCD

RCD parameter
Letter designation
Description
Additional Information
Rated voltage
Un
The voltage level that is selected by the manufacturer of the device and is necessary for its operation.
Usually the nominal voltage is 220 V, sometimes 380 V

Uniform voltage in the mains and the rated voltage of the differential current switch, as the RCD is also called, is an important condition for the trouble-free operation of the device.
Rated current
In
The highest value of current at which the RCD operates for a long period.
The value of the rated current can be as follows: 10, 13, 16, 20, 25, 32, 40, 63, 80, 100 or 125 A. In relation to the differential machine, this value also acts as the rated current of the circuit breaker in the RCD configuration

For differential automata, the value of the rated current is selected from the range: 6, 8, 10, 13, 16, 20, 25, 32, 40, 63, 80, 100, 125 A.
Rated residual breaking current
Idn
leakage current.
This characteristic of the residual current device is considered the main one, since it indicates what value of the differential current will make the device react. RCDs are produced with the following parameters of the rated differential breaking current: 6, 10, 30, 100, 300 and 500 mA.
Rated conditional short-circuit current
Inc
An indicator by which one can judge the reliability, strength and quality of the RCD.
The rated conditional short circuit current indicates how well the electrical connections of the machine are made. The value of the rated short circuit current is standardized and can be equal to 3000, 4500, 6000 or 10000 A.
Rated residual short-circuit current
IDc
Another indicator of the quality and reliability of the device.
Similar to rated conditional short circuit current. The only difference is that the overcurrent passes through one conductor of the residual current device, and the testing of the operation of the device is carried out after the test current is turned on in turn on different poles of the RCD.
Limit value of non-switching overcurrent
—
This is a characteristic that reflects the ability of the residual current circuit breaker to ignore symmetrical short-circuit currents and situations when the network is overloaded.
This indicator has nothing to do with the current value at which the residual current device is required to block the power supply. The minimum indicator of non-shutdown current must correspond to the value rated load currentmagnified 6 times.
Rated making and breaking (switching) capacity
Im
A parameter that depends on the degree of technical preparation of the RCD, that is, on the power of the spring drive, the raw materials used and the quality of the power contacts.
Switching capacity can be equal to 500 A or 10 times exceeding the level of rated current
For quality devices it is 1000 or 1500 A.
Rated residual current making and breaking capacity
IDm
Characteristic, which is also determined by the technical design of the residual current circuit breaker.
This parameter is comparable to the previous one (Im), but differs from it in that the differential current flow is taken into account. Often it is evaluated during a short circuit to the body of the electrical receiver in the TN-C-S system.

Rated (capacity) current RCD

The value of this electrical characteristic directly depends on the number and power (Watts) of your electrical appliances. Those. the general (introductory) RCD must have a rated current designed for all household electrical appliances installed with you. For a linear protection device, the total power of the devices on a given wiring line is calculated.For example, if you have an RCD installed separately for the kitchen, then you calculate the total power for electrical appliances installed in the kitchen. The current strength (I, Amperes) is calculated by the formula: I \u003d P / U, where P is power (Watts), U is voltage (Volts).

The principle of operation of the RCD

To prevent accidental electric shock when in contact with household and industrial electrical appliances, a residual current device was invented.

It is based on a transformer with a toroidal core, which monitors the current strength on the "phase" and "zero". If its levels diverge, then the relay is activated and the power contacts are disconnected.

You can check the RCD by pressing the special "TEST" button. As a result, a current leakage is simulated, and the device should disconnect the power contacts

Normally, any electrical device has a leakage current. But its level is so small that it is safe for the human body.

Therefore, RCDs are programmed to operate at a current value that can cause electrical injury to people or lead to equipment breakdown.

For example, when a child sticks a bare metal pin into a socket, electricity will leak through the body, and the RCD will turn off the light in the apartment.

The speed of operation of the device is such that the body will not experience any negative sensations at all.

The RCD adapter is convenient for the ability to quickly move between outlets. It is suitable for people who do not want to install fixed protective devices.

Depending on the power of the connected equipment, the presence of intermediate protective devices and the length of the wiring, RCDs with different limit values ​​​​of differential currents are used.

The most common in everyday life protective devices with a threshold level of 10 mA, 30 mA and 100 mA.These devices are sufficient to protect most residential and office premises.

It should be remembered that the classic RCD does not protect the electrical wiring from a short circuit and does not turn off the power contacts when the network is overloaded. Therefore, it is desirable to use these devices in combination with other electrical protection mechanisms, such as circuit breakers.

How to choose the right RCD by parameters

The choice of RCD must be carried out, paying attention to its rated and differential operating current. Rated - this is the current for which the operation of the power contacts is designed. If it is increased, they may fail.

Differential is the tripping current of the residual current device, that is, leakage

If it is increased, they may fail. Differential is the tripping current of the residual current device, that is, leakage

Rated - this is the current for which the operation of the power contacts is designed. If it is increased, they may fail. Differential is the tripping current of the residual current device, that is, leakage.

Before choosing an RCD, it is useful to find out its price, quality and performance and compare these three parameters. Since it can be difficult for a non-professional to choose an RCD in terms of power and quality, experts advise compiling a table of parameters for the devices you like and using it to choose a device with the best characteristics.

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Rated current

When selecting by rated current, you need to know that the device is always placed in series with automatic switch for protection of power contacts against overload and short circuit. When one or the other occurs, the device does not work, as it is not intended for this.Therefore, it must be protected automatically.

The next thing you should pay attention to: the rated current must at least match the declared for the machine, but it is better to be 1 step higher

Residual current

There are two important things to remember here:

1. For electrical safety, a differential trip current of either 10 mA or 30 mA is always selected. For example, a 10 mA RCD can be installed on one electrical receiver. At the entrance to the house, a device with this value may work too often, since the electrical wiring in the apartment has its own leakage limits.
2. All other RCDs with a differential current above 30 mA are used for fire fighting purposes. But when installing a 100 mA RCD at the input, a 30 mA RCD must be installed in series with it for electrical safety purposes. In this case, it would be advisable to install a selective RCD at the input so that it operates with a short time delay and makes it possible to operate a device with a lower rated current.

Product type

According to the form of current leakage, all these devices are classified into 3 types:

1. Device type "AS". This device is common because of the more affordable price. Operates only when a sinusoidal current leakage occurs.
2. Type "A" device. It is designed to operate with an instantaneous or gradual appearance of excess current, which has a variable sinusoidal and pulsating constant shape. This is the most sought after type, but is more expensive due to the ability to control both constant and variable flow.
3. Type "B" device. Most often used to protect industrial premises.In addition to responding to a sinusoidal and pulsating waveform, it also responds to a rectified form of constant leakage.

In addition to these main three types, there are 2 more:

1. Selective device type "S". It does not turn off immediately, but after a specified period of time.
2. Type "G". The principle is the same as the previous one, but there the time delay for shutdown is slightly less.

Design

By design, 2 types of RCDs are distinguished:

• electronic - working from an external network;
• electromechanical - independent of the network, for its operation, power is not needed.

Manufacturer

An equally important criterion is the choice of the manufacturer. The question of which RCD company is better to choose must be decided by the buyer himself. The following options are recommended:

• Legrand;
• ABB;
• AEG;
• Siemens;
• Schneider Electric;
• DEKraft.

Among budget models, Astro-UZO and DEC have the highest quality.

Types of RCD

Parameters, by which can be subdivided protective devices:

• Control method - dependent and independent of voltage;
• Purpose - with built-in overcurrent protection and without it;
• Installation method - stationary and independent;
• The number of poles is two-pole (for a single-phase network) and four-pole (for a three-phase network).

Electromechanical RCD

Electromechanical RCD - "veteran" protection against current leakage. The device was patented back in 1928. In most European countries, it is the electromechanical safety device that is mandatory for use as protection against residual current.

The presence of voltage for the performance of an electromechanical RCD does not matter. The source of energy for performing protection functions is the leakage current, to which the circuit breaker reacts.

The basis of the device is the accuracy and reliability of mechanics. The magnetic core of the transformer has high sensitivity, as well as temperature and time stability. It is produced from nanocrystalline or amorphous alloys, which are characterized by high magnetic permeability.

Advantages:

• Reliability - a serviceable device guarantees 100% operation in case of current leakage, regardless of the presence of voltage in the network;
• Retains functionality even if the neutral conductor breaks;
• It has a simpler design, which increases the reliability of the switch;
• Does not require auxiliary power sources.

Flaws:

High price (depending on the brand, the price can be three times or even five times higher than the price of an electronic device).

Electronic RCD

Inside the device there is an amplifier on a microcircuit or a transistor, due to which the switch is triggered even if a slight current occurs in the secondary winding. The amplifier ramps it up to the pulse size needed to activate the relay. But for the operability of the elements of an electronic RCD, the presence of voltage in the network is necessary.

The question arises of the need for an RCD in the absence of voltage in the network. What to protect yourself from? If the voltage is lost due to a break in the neutral conductor in the circuit to the RCD, then a dangerous potential for humans continues to flow to the electrical installation through the phase conductor.

Advantages:

• Low price;
• Compactness.

Flaws:

• Operates only when voltage is present;
• Inoperable when the neutral is broken;
• A more complex design increases the likelihood of circuit breaker failure.

RCD portable and in the form of a socket

A simple solution that can protect against leakage current is portable RCDs and in the form of a socket.They are convenient when used in the bathroom and other rooms with high humidity, they can be connected to any of the rooms of the apartment, where necessary.

Most of the proposed models are made in the form of a power adapter with a socket hole for a plug. Even a child can use such a device - it is connected directly to the outlet, and then the appliance is turned on.

Easy to use and extension cords with RCD function, designed for several consumers.

There are models that are less versatile, they can be used after being installed on the cord of an electrical appliance instead of a plug, or they can be installed instead of a conventional electrical outlet.

Advantages:

• Installation does not require intervention in the wiring;
• Installation does not require the assistance of an electrician;
• The operation of automation allows you to determine in which consumer the insulation is damaged.

Flaws:

• Using the adapter in visible places brings disharmony to the design of the room;
• In a room that is cluttered with furniture and electrical appliances, and the space in front of the outlet is limited, there may not be free space for installing the adapter;
• High cost - a quality adapter will cost more than an RCD and socket purchased separately.

RCD with overcurrent protection (difavtomat)

The device combines the functions of an RCD and a circuit breaker, which is designed to protect against overcurrents (prevents wiring from overload and damage short circuit).

Advantages:

• Profitability - buying one device will cost less than two;
• Takes up less space in the dashboard;
• Saving time during the installation process.

Flaws:

• When the circuit breaker fails, the line will be unprotected both from leakage currents and from overcurrents;
• In the event of a device tripping, there is no way to determine what caused it - overcurrents or leakage current;
• False positives caused by office equipment. It is not recommended to install difavtomatov on the line to which computers and office equipment are connected.

Power calculation for RCD

Each individual device has its own threshold current load, at which it will work normally and will not burn out. Naturally, it must be higher than the total current load of all devices connected to the RCD. There are three types of RCD connection schemes, for each of which the calculation of the power of the device is different:

• A simple single-level circuit with one protection device.
• Single-level scheme with several protection devices.
• Two-level trip protection circuit.

Calculating power for a simple single-level circuit

A simple single-level circuit is characterized by the presence of one RCD, which is installed after the counter. Its rated current load must be higher than the total current load of all consumers connected to it. Suppose the apartment has a boiler with a capacity of 1.6 kW, a washing machine for 2.3 kW, several light bulbs with a total of 0.5 kW and other electrical appliances for 2.5 kW. Then the calculation of the current load will be as follows:

(1600+2300+500+2500)/220 = 31.3 A

This means that for this apartment you will need a device with a current load of at least 31.3 A. The nearest RCD in terms of power is 32 A. It will be enough even if all household appliances are turned on at the same time.

One of such suitable devices is the RCD ERA NO-902-126 VD63, designed for a rated current of 32 A and leakage current at 30 mA.

We calculate the power for a single-level circuit with several protection devices

Such a branched single-level circuit assumes the presence of an additional bus in the meter device, from which wires depart, forming into separate groups for individual RCDs. Thanks to this, it is possible to install several devices on different groups of consumers or on different phases (with a three-phase network connection). Usually a separate RCD is installed on the washing machine, and the rest of the devices are mounted for consumers, which are formed into groups. Suppose you decide to install an RCD for washing machine capacity 2.3 kW, a separate device for a 1.6 kW boiler and an additional RCD for the rest of the equipment with a total power of 3 kW. Then the calculations will be as follows:

• For a washing machine - 2300/220 = 10.5 A
• For a boiler - 1600/220 = 7.3 A
• For the rest of the equipment - 3000/220 = 13.6 A

Given the calculations for this branched single-level circuit, three devices with a capacity of 8, 13 and 16 A will be required. For the most part, such connection schemes are applicable for apartments, garages, temporary buildings, etc.

By the way, if you don’t want to bother with installing such a circuit, then pay attention to portable RCD adapters that can be quickly switched between sockets. They are designed for one appliance.

We calculate the power for a two-level circuit

Principle device power calculation protective shutdown in a two-level circuit is the same as in a single-level one, with the only difference being the presence of an additional RCD located at the entrance to the apartment, up to the meter. Its rated current load must correspond to the total current load of all devices in the apartment, including the meter.We note the most common RCD indicators for current load: 4 A, 5 A, 6 A, 8 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, etc.

The RCD at the input will protect the apartment from the occurrence of a fire, and the devices installed on individual groups of consumers will protect a person from electric shock. This scheme is the most convenient in terms of repairing electrical wiring, as it allows you to turn off a separate section without turning off the whole house. Also, if you need to repair cable systems at the enterprise, you will not have to turn off all office premises, which means there will be no massive downtime. The only drawback is the considerable cost of installing an RCD (depending on the number of devices).

If you need to select an RCD for a group of machines for a single-phase network, then we can advise the ERA NO-902-129 VD63 model with a rated current load of 63 A - this is enough for all electrical appliances in the house.

RCD power table

If you are thinking about how to easily and quickly select an RCD by power, the table below will help you with this:

How does the protection device work?

The connection of the protective module to the main electrical system is always carried out after the introductory circuit breaker and the electricity meter. RCD with one phase, designed for a network with a standard indicator of 220 V, has in its design 2 working terminals for zero and phase. Three-phase units are equipped with 4 terminals for 3 phases and a common zero.

Being in the activated mode, the RCD compares the parameters of the incoming and outgoing currents, and calculates how many amperes go to all the electrical consumers in the room.When working correctly, these indicators do not differ from each other.

Sometimes an RCD can trip for no apparent reason. Usually this situation is provoked by sticky buttons and imbalance of the device caused by too intense operating load or condensation.

The difference in performance between the input and output currents clearly indicates that there is an electrical leak in the house. Sometimes it occurs due to human contact with a bare wire.

The RCD detects this situation and immediately de-energizes the controlled section of the network in order to protect the user from a potentially possible electric shock, burns and other household injuries associated with electricity.

The lowest threshold at which the residual current device trips is 30 mA. This indicator is called the level of non-letting go, at which a person feels a sharp current shock, but can still let go of an object that is energized.

With an alternating voltage of 220 V with a frequency of 50 Hz, a current of 30 milliamps is already felt very strongly and causes convulsive contraction of the working muscles. At such a moment, the user cannot physically unclench his fingers and throw aside a part or wire that is under high voltage.

All this leads to dangerous situations that threaten not only health, but also life. Only a well-chosen and correctly installed RCD can prevent these troubles.