How to choose the shutdown current of the difavtomat 10mA or 30mA? Type “A” or “AC” and release characteristic “B” or “C”?

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Difavtomats perform a double function (protect against electrical leaks and short circuits) and completely replace the set of RCD and circuit breaker. When choosing a differential, you must consider the following characteristics:

• Circuit breaker rating (A);
• Leakage at which the mechanism is triggered (mA);
• Trip characteristic (“A” or “AC”);
• Type of mechanism (electronic or electromechanical);
• Release characteristics of the machine (B or D).

But how to choose specific values? Taking the opportunity, and not for the first time turning to our electrical engineering expert, I decided to ask him these questions. Namely, the engineer, and part-time specialist in the sale of differential protection, Sergei from the AxiomPlus online electrical equipment store. And this time, although reluctantly, he carried out another educational program.

• How to calculate and determine the right automatic machine for yourself?
• Which release rating should I choose?
• Trip characteristic "A" or "AC"?
• Which type of release should I choose?
• Select the release characteristic of the machine: “B” or “C”

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Scheme

When designing a wiring diagram for an apartment or house, there can be many options. They may differ in ease of use, reliability of operation, and degree of protection. There are simple options that require minimal costs. They are usually implemented in small networks. For example, in dachas, in small apartments with a small number of household appliances. In most cases, it is necessary to install a large number of devices that ensure the safety of the wiring and protect people from electric shock.

Schemes come in different levels of complexity

Simple scheme

It does not always make sense to install a large number of protective devices. For example, at a dacha for a seasonal visit, where there are only a few sockets and lighting, it is enough to install only one difavtomat at the entrance, from which separate lines will go to groups of consumers - sockets and lighting - through the machines.

A simple diagram for connecting a difavtomat to a small network

This scheme will not require large expenses, but if a leakage current appears on any of the lines, the difavtomat will work, de-energizing everything. There will be no light until the causes are clarified and eliminated.

More reliable protection

As already mentioned, some automatic machines are placed on “wet” groups. These include the kitchen, bathroom, outdoor lighting, and appliances that use water (except the washing machine). This method of building a system provides a higher degree of safety and better protects wiring, equipment and people.

A more complex and reliable scheme: connecting a difavtomat to every potentially dangerous device

The implementation of this wiring method will require large material costs, but the system will operate more reliably and stably. Since when one of the protective devices is triggered, the rest will remain operational. This connection of the difavtomat is used in most apartments and small houses.

Selective schemes

In extensive power supply networks, there is a need to make the system even more complex and expensive. In this option, an input differential circuit breaker of class S or G is installed after the meter. Further, each group has its own circuit breaker, and, if necessary, they are also installed for individual consumers. See the photo below for connecting the difavtomat for this case.

Selective installation diagram of a difavtomat

With this design of the system, when one of the linear devices trips, all the others will remain in operation, since the input differential switch has a delay in response.

Features of choosing an automatic machine for a washing machine

Typically, the older the model, the greater the starting current. However, even for new manufacturers this figure is often 3-5 times the rated load. In this case, tripping characteristic “B” will no longer be suitable , since it will define a power surge three times higher than the nominal value as a short circuit.

Imagine a situation when you fill a drum with clothes, then add washing powder, set the optimal mode and press the start button. The door is blocked, the drum is filled with water and suddenly the light goes out. The machine remains blocked, and the washing mode has gone wrong.

To prevent this from happening, select the “C” release characteristic. Contacts with it are instantly broken only if the load is 5 times higher than the nominal value. For old “washers”, it’s better to play it safe and take “D”. It can withstand starting currents equal to 10 rated.

The rating of the machine must be no less than the power of the washing machine. In some modes, the washing duration exceeds an hour, in addition, load fluctuations will periodically occur: starting/stopping the drum, spinning, etc. Therefore, it is better to take an equal denomination or the next one up, but not less.

Based on the fact that the washing machine is sensitive to power surges , it is recommended to install a stabilizer along with a separate machine. Usually, even a slight deviation of voltage from the norm disables it.

If, in order to save money, you can install one RCD for the entire bathroom, then it is better to install a stabilizer individually on the “washing machine”. In contrast, a slightly different principle for selecting characteristics is used for the air conditioner.

Purpose of residual current devices

The RCD protects the insulation of electrical wiring and prevents fire.
And it protects a person from exposure to electric current when touching parts of devices that have phase voltage. The RCD is triggered by an imbalance of currents in the phase and neutral wires of the protected electrical network. This happens when an insulation breakdown occurs and an additional leak appears.

Flowing current through unauthorized materials may result in a fire. In buildings with dilapidated electrical wiring, fires from damaged insulation occur quite often.

Another dangerous case is touching live parts of devices that should not be energized under normal conditions. The current begins to flow to the ground through the person, bypassing the neutral wire.

In this case, the circuit breaker will not work, since it requires currents of at least tens of amperes to turn off. Currents starting from 30 mA and above are dangerous to human life. The ability of the residual current device to respond to 10-30 mA is reliable protection against the effects of electricity.

If the question is what to choose - an RCD or a difavtomat - you need to understand that together with the RCD you will definitely have to install a circuit breaker in the circuit.

The difavtomat is used to protect the electrical network from overload, short circuit and leaks. In addition to the capabilities of an RCD, it performs the functions of a circuit breaker.

It happens that a person connects an extension cord with five or six additional sockets to one outlet, and connects several powerful devices through them. In such circumstances, overheating of the conductors is inevitable.

Or, let’s say, when the electric motor is turned on, the shaft jams, the winding begins to heat up, after some time a breakdown occurs, followed by a short circuit of the wires.

To avoid this, a difavtomat is installed. If the current excess is significant, then the difavtomat will turn off the line within a few seconds, without waiting for the insulation to melt, thereby preventing a fire.

The speed of switching off the automatic circuit breaker depends on how many times the flowing current exceeds the rated current for a given line. If the voltage is exceeded multiple times, up to a short circuit, the electromagnetic release is instantly triggered.

If the current flowing through the line exceeds the rated current by more than 25%, then after about an hour the device will turn off the line and the thermal release will operate.

If the excess is greater, the shutdown will occur much earlier. The response time can be determined from the time-current characteristics given for each device.

Modern homes are literally filled with various equipment and household appliances, many of which are highly powerful. In this regard, the load on the electrical wiring increases significantly, and the likelihood of damage and failure of the insulation after a certain period of operation increases. As a result, the wiring through the damaged insulation is connected to the ground, and the flow of current changes its direction, that is, a current leakage occurs. When coming into contact with dangerous places, a person himself becomes a conductor and can receive serious injuries.

Modern washing machines are also among household appliances with increased energy consumption. They gain maximum power in the range of 3-3.5 kW during operation of the heating element and heating of water. If the insulation is damaged, current leakage can also reach a large value that is dangerous to human life. Therefore, experts recommend installing a separate RCD on the line supplying the washing machine. In the event of a leak, the RCD will simply turn off the network and stop supplying voltage.

To connect the RCD with the consumer into a single circuit, a serial connection is used. The principle of operation of the device is based on measuring and comparing the difference in current at the input and output. If the network is healthy, it will have a zero value. And in the event of a leak, the output current will differ downward by exactly the amount that went along the other path. When the current leakage value for which the device is installed is reached, it will instantly react and turn off the network.

Deciding on the denomination

Actually, from the functions of the circuit breaker, the rule for determining the rating of the circuit breaker follows: it must operate until the current exceeds the capabilities of the wiring. This means that the current rating of the machine must be less than the maximum current that the wiring can withstand.

For each line you need to choose the right circuit breaker

Based on this, the algorithm for selecting a circuit breaker is simple:

• Calculate the wiring cross-section for a specific area.
• See what maximum current this cable can withstand (see the table).
• Next, from all the ratings of the circuit breakers, we select the nearest smaller one. The ratings of the machines are tied to the permissible long-term load currents for a particular cable - they have a slightly lower rating (see the table). The list of denominations looks like this: 16 A, 25 A, 32 A, 40 A, 63 A. From this list you choose the appropriate one. There are smaller values, but they are practically not used anymore - we have too many electrical appliances and they have considerable power.

Example

The algorithm is very simple, but it works flawlessly. To make it clearer, let's look at an example. Below is a table that shows the maximum permissible current for conductors that are used when laying wiring in a house and apartment. Recommendations regarding the use of machines are also given there. They are given in the column “Nominal current of the circuit breaker”. This is where we look for the ratings - it is slightly less than the maximum permissible for the wiring to work normally.

Main settings

To understand how to choose a differential machine, you need to understand its characteristics. For installation in a residential building, the differential circuit breaker must be turned off when the differential current is no more than 30 milliamps. This is a general requirement imposed by the electrical installation rules (PUE).

This meaning is justified. A direct current of 50 mA and an alternating current of 10 mA are considered dangerous for the human body.

The second parameter by which the automatic machine is selected is the rated current. It must correspond to the maximum current value in the protected section of the circuit. This parameter depends on the amount of load and the conductor used. The same parameter is taken into account when protecting against short circuit (short circuit).

Selection of circuit breaker rating based on wire cross-section

Having determined the rating of the machine based on the power of the “suspended” load, you need to make sure that the electrical wiring can withstand the appropriate current. As a guide, you can use the table below, compiled for a copper wire and a single-phase circuit (Table 3):

As you can see, all three indicators (power, current and wire cross-section) are interconnected, so the rating of the machine can, in principle, be selected according to any of them. At the same time, it is necessary to make sure that all parameters fit together and, if necessary, make appropriate adjustments.

In any case, remember the following:

1. Installing an overly powerful circuit breaker can lead to the fact that before it operates, electrical equipment that is not protected by its own fuse will fail.
2. A machine with a low number of amperes can become a source of nervous stress, cutting off power to the house or individual rooms when the electric kettle, iron or vacuum cleaner is turned on.

Malfunctions

There are often cases when the RCD turns off when the water heater or washing machine is turned on. There are a number of reasons for this:

• the water heater or machine itself is faulty;
• the installed RCD or automatic circuit breaker does not correspond to the parameters of the electrical network;
• there is a short circuit in the power cord;

• the motor, power supply or heating element is damaged;
• the installation of the RCD for the washing machine or water heater was carried out with errors;
• Voltage surges or current leaks have occurred in the electrical network.

Self-installation

To connect an automatic protective switch in the electrical panel, first install the upper part of the switch on the DIN rail . Use a screwdriver to pull out the eyelet and press the lower part. The lower grip is released and snapped into place.

Then the contacts are connected. If stranded conductors, crimped with lugs, were previously connected, they are inserted back into the upper and lower clamps and the screws are tightened. If the core was without a tip, it is better to remove and clean the old end, then use a screwdriver to make a fresh, undeformed conductor.

After connecting the wires, voltage is applied to the machine and its operation is checked. If everything is in order, connect electrical appliances and make sure that no sparks, crackling, heating or other undesirable effects appear at the switch contacts. Heating is checked with a pyrometer.

It is important to choose the correct ratings of the circuit breakers, the diameter of the copper conductors, and install the breaking phases and not the neutral wire. The machines are installed in the operating position by sliding the switch buttons up.

Other differences

Already from the purpose of the devices it becomes clear what the difference is between them. The difavtomat is more universal; it includes RCD functions. But beyond the features and appearance, there are other differences.

Price

An important difference is the price. A differential circuit breaker is significantly more expensive than an RCD. Even if the RCD is functionally equal to that of a difavtomat by connecting an additional circuit breaker, the cost of the difavtomat will still be higher.

The occupied volume of such a design due to the additional automatic machine will be one and a half times greater than the space for the automatic machine. This is important for small electrical panels.

But the maintainability of devices with equal functionality is better in an RCD automatic machine system than in a simple automatic device. In addition, the reason for the shutdown immediately becomes clear - leakage currents or network overload.

Connection

But when installing a differential switch, you don’t have to think about how to install an RCD or connect it before or after the machine. In fact, most experts recommend installing the circuit breaker first, then the differential one.

As for the RCD, there are two options. If the RCD is installed on several groups of consumers, then it comes first, followed by circuit breakers for each group.

If one line is protected by one RCD and one machine, then the machine goes first.

So, the main difference between a difavtomat and an RCD is their functions, markings, cost, connection method and space taken up in the panel.

What is best to use is decided by each owner independently. The main thing is to connect all devices correctly and provide reliable protection against fire or electric shock.

Which RCD should I install on my washing machine?

The average user wants to know which protective device to install on the washing machine. Most models consume 2 kW, and this exceeds the nominal value of 10 A. Therefore, an automatic or automatic device must operate with an electric current greater than 10 A. Choose the 16 A option.

Among the important parameters of automatic protection is leakage current. The device reacts precisely to it. If the wiring is new, take the 10 mA option. For a circuit break to occur, the difference in current between phase and neutral must be 10 mA or more. If the wiring is old, use a 30 mA RCD to avoid erroneous shutdowns.

Another nuance that is important to pay attention to when choosing an automatic machine to connect to a washing machine is the manufacturer. There are two options:

• Expensive and high quality - Legrand or ABB.
• Budget - IEK.

These are the most famous companies on the market that produce protective automation. Chinese versions are cheaper, but they will not provide the reliability that European devices provide. If you select the wrong power and electric current, the plugs will be knocked out every time you start the machine.

Characteristics of difavtomats

So, let's assume that you decide to buy a automatic machine. How to understand which option is right for you? Let's look at the main designations of difavtomats.

Modules, poles, phases.

These concepts are often confused. Let's do it this way.

• Phase is what system the difavtomat is designed for. There are only two options - 1 phase (domestic) and 3 phases.
• Polarity is the number of clamps on a difavtomat. That is, this is how many lines you need to connect. There are two-pole difavtomats (for single-phase networks) and four-wheel difavtomats (for three-phase networks).
• The number of modules is the size. For example, two-pole automatic circuit breakers (for single-phase networks) are usually made two-module (that is, they occupy 2 modules in the panel). But they also come in single-module (super compact) and three-module (usually very budget options).

If you choose a difavtomat for an apartment, 90% of the time you need a two-module, two-pole and single-phase difavtomat.

Features of machines for sockets of some famous brands

In hardware stores you can see a large assortment of circuit breakers from different manufacturers. Some of them use their own marking system; you can get acquainted with the characteristics of the model using a special catalog number.

The most popular and reliable circuit breakers include:

• "ABB" - machines with a modular design. The developers are a Swedish-Swiss company. They produce different modifications designed for different voltages and rated currents.
• "AE" is an effective device made in Russia. This protective fitting is produced in different configurations, so there should not be any difficulties in choosing a suitable device.

Also, when choosing a circuit breaker for your home, you should pay attention to Legrand. Most foreign manufacturers manufacture their products under license in Russian and Chinese factories.

Domestic models

KEAZ is a domestic manufacturer of differential circuit breakers and other protection devices. The quality is average, but the products come with a two-year warranty. The price is 1000-1500 rubles for single-phase products.

IEK is also a domestic brand. The products are in great demand due to the successful combination of price and quality. In fact, product shortcomings, such as imperfect terminals, noise during operation, are compensated by the price of 700-1000 rubles for single-phase products.

DEKraft is another Russian brand. The company was formed relatively recently. The quality of the products leaves much to be desired, but at the same time the products comply with Russian standards. The disadvantage is the short service life of the products. Considering the low price (600-1000 rubles), contractors willingly use products of this brand for installation on low-budget projects.

Many manufacturers often produce budget automatic machines, and even entire lines of models with low prices. Therefore, when choosing, it is recommended to carefully study product catalogs.

Of course, when choosing a differential machine, you need to focus not only on price and manufacturer. The operating conditions of the device must be taken into account.

It is possible to use devices with a lesser degree of reliability in utility rooms, where the specific time of use of electrical wiring is small. If the need for such automatic machines is great, then the cost savings can be significant.