Differential protection devices: difavtomat or ouzo

The impact of electricity has a detrimental effect not only on human life and health, but also on the entire range of consumers who fail without proper protection. Differential protection devices are widely used. Which is better: ouzo or differential automaton? To answer this question, you need to study them in detail, and then draw conclusions.

Residual current devices

When installing electrical wiring or upgrading it, circuit breakers are not enough. The main criterion is electrical safety, because electricity not only has useful properties, but can also lead to huge problems (financial difficulties, threat to health and life).

To protect electrical wiring, devices and devices, specialized devices are used, which are called differential current devices. They protect not only from current leakage and from exceeding the electrical performance of the network, but also from short circuits. This is a necessary measure, because you cannot control electricity while, for example, at work. This often leads to equipment failure, accidental fires and fires.

In our time, a differential machine and an RCD are widely used. And many are very worried about ouzo or difavtomat - what to choose?

Trouble using home wiring

Before proceeding with the selection of a differential protection model, it is necessary to find out from what adverse factors the power grid should be protected.

The main problems of an unsecured network:

1. Overloading the network occurs when the wiring is simply not designed for the total power consumption. Causes of occurrence: the old wiring does not withstand the load of consumers and the simultaneous inclusion of powerful devices. The use of tees should also be avoided, as the load on the outlet must be acceptable. The consequence of all this is heating of wires, melting of socket cases, short circuit, failure of devices and fire.
2. A short circuit occurs when the current has reached its maximum value (the main condition for normal operation is the presence of an acceptable resistance). There can be many reasons: direct contact of the phase and neutral wire of the mains, ingress of strangers conductors, etc. This leads to an instant rise in the temperature of consumers, their failure and fire. In some cases, an electric arc may occur (temperatures range from 4000 to 18000 degrees Celsius).
3. Leakage currents are generated by touching an energized enclosure. This creates an unauthorized chain. This current can cause equipment breakdowns and a threat to human life.

Danger in the home - This is an electric shock to a person. For example, when you touch the pump, microwave oven, you feel the unpleasant effect of the current on the human body. This is where the danger lies, because today a weak blow will occur, and after a while the phase will give a breakdown in the product body.

According to the provisions of electrical safety, a voltage of 220V and a current of 1.5mA are safe for humans. At currents up to 7 mA, convulsive phenomena are felt, and at 10 mA, a person is no longer able to tear off his hand from the current-carrying part.

But these values ​​in real life are significantly different. It all depends on the resistance of the human body and on the way of touching. Body resistance depends on many factors, some of them are: air humidity, moisture on the floor, shoes, clothes, genetic characteristics, nutrition, and even mood.

Differential protection selection criteria

In order to clarify the next problem of choice (difavtomat or ouzo - which is better?), You must first of all disassemble their principle of operation, scope of application, design features, occupied space, cost, complexity of repair and connection, troubleshooting, ease of installation.

Design and installation features

For home conditions, single-phase ouzo are usually used and have a two-pole design. They must be used together with a circuit breaker, because OUZO protects the power grid or a section of the circuit from leakage currents, and the circuit breaker protects from overloads and short circuits. This design occupies 3 modules in the dashboard.

Ordinary single-phase difavtomat made 2-module, however, there are models that are available in a single-module design. If there are several difavtomats or several ouzo, then the space savings will be significant.

It is not difficult to install an ouzo or difavtomat - convenient clamps allow you to do this without problems, but there are also some nuances here.

For comparison, diagram 1 shows the switching of a pair of ouzo with an automatic machine and a difavtomat. Therefore, connecting a difavtomat is much easier.

Scheme 1 - Scheme of comparison of switching of an OUZO + an automatic machine and a difavtomat

Diagnostics and maintainability of circuits

Each of the considered differential protection devices is designed for open circuit in case of operation. To find out the reason for the triggering, it is necessary to perform some diagnostics.

With a pair (ouzo and circuit breaker) installed, the problem can be identified immediately. When the ouzo was triggered, a current leak occurred on a line. If the circuit breaker has tripped, then there is an overload or short circuit in the electrical network.

But if a difavtomat is installed, it becomes more difficult to identify the cause. Some expensive models are equipped with a special indication that signals a leak or overload.

Differential protection devices can also fail. For example, with frequent tripping for no reason or with a clearly congested line. In this case, the thermal protection circuit is most likely faulty (malfunctions of the bimetallic plate). In the case of a pair of RCDs and AB, as a rule, 1 element fails, which can be replaced, which is cheaper than purchasing a difavtomat.

The principle of operation of the RCD and difavtomat

An RCD is used for identification and protection against leakage currents. The principle of operation is based on comparing the values ​​of the currents (incoming and outgoing).

Figure 1 - RCD (Residual current device or differential switch)

RCD device:

1. Toroidal transformer with 2 primary windings and one control winding.
2. Electromechanical relay (key).

The control winding is connected to the key, and during normal operation of the device, the currents on the 2 primary coils create magnetic fluxes. Moreover, these coils are wound in opposite directions. When added, these magnetic fluxes give a net magnetic flux in the core equal to zero. However, when a leakage current appears, this rule is violated, and on the control coil, due to the difference in magnetic fluxes other than zero, a magnetic flux is formed on the control coil. This magnetic flux triggers the key and the circuit is opened. The response time of the RCD (differential switch) is in the range from 0.2 to 0.3 seconds.

Particularly widespread devices 30 mA, and in rooms with high humidity - 10 mA.

A differential automatic device or an automatic differential current switch (RCBO) combines an RCD and an AV (automatic switch).

Figure 2 - Difautomat

Absolutely all RCBOs surpass RCDs in response speed (0.04 seconds) and allow you to quickly turn off the power in sections of the circuit with voltage surges above 250V.

Price

The solution to this issue is quite simple. The cost of a pair of RCD and AB is lower than the cost of the difavtomat itself. Indeed, if any element of this pair fails, it is necessary to replace the AV or RCD (cheaper than changing the difavtomat). It is advisable to immediately purchase high-quality devices, because a miser pays twice. And when buying a high-quality differential protection device, there are fewer problems. Top brands include Schneider Electric, General Electric and ABB.

An example showing how to select a particular device.

A powerful device (15A and 1.5 kW) was purchased, to which it is necessary to supply a separate power line. For this case, you will need AB for 16A and an RCD (30mA). It is necessary to add up the costs of the devices and compare the resulting cost with the price of the RCBO. If it is necessary to put protection on 8 lines, each of which consists of 4 groups for a pair of RCDs and AB: 6 AB * (the cost of one AB) + 3 RCDs * (the cost of the 1st RCD).

There is nothing to be done for difavtomats, since they need 8 pieces (1 RCBO for 1 line). We calculate the amounts and find out that the installation of RCBOs is much more expensive.

Main advantages and disadvantages

Having clarified the differences between the two differential protection devices, a number of advantages and disadvantages can be formed.

However, it is quite difficult to find out, because it is necessary to be guided by the specific situation and parameters of the wiring lines, as well as the devices connected to this network.

The main disadvantages of the difavtomat:

1. Diagnostic problem: it is difficult to diagnose the cause of the device triggering, although there are expensive models that provide this function.
2. The financial side: it is more expensive than an RCD and in case of failure it is necessary to buy a new one.

Disadvantages of RCDs:

1. High response time relative to RCBO.
2. Takes up more space during installation.
3. Must be used together with AB.

Advantages of the difavtomat:

1. High response speed.
2. Ease of installation.
3. Takes up less space in the box.

Advantages of RCDs with AB:

1. Relatively low price.
2. Easy diagnostics.
3. Better maintainability.

If we take into account that the reliability of the RCD + AV and RCBO is the same (budget options are not considered), then the main criterion for choosing a particular device is, first of all, its cost. After all, it all depends on financial capabilities.

The main aspects when choosing, which are worth paying attention to:

1. Installation and connection diagrams: no particular difficulty.
2. Diagnostics: when connecting a RCBO, finding the cause is not a problem, because there is a light indication.
3. There is no need to save on a spacious dashboard, perhaps one day you will need to draw another line, which must also be protected.

Thus, when choosing a specific differential protection device, it is necessary to think over everything, draw up an approximate plan for dividing the power supply lines of a residential premises, decide on consumers, calculate the total possible capacity of consumers for each line and, based on the financial situation, make the final choice. The main difference and the main criterion is the price, but you should not save money, because this is your safety, as well as minimizing financial problems.