High-quality automatic protection is a guarantee of safety

If you managed to intervene in the process of building an electrical network at the first stages, then you may already be using NYM cable and Hensel distribution boxes ... And this largely protects you from problems related to electrical wiring. But what if the wiring was done without you and you don't know about the quality of its execution? It could be worse — you assume poor quality and don't have the option to redo everything.

In addition, problems in the electrical network can occur not only due to poor-quality wiring, but also due to its unexpected failures or due to the failure of end devices (short circuit or overload due to fire). In this case, various protective devices can become a guarantee of your peace of mind. Many of them are invented and we will talk about many in the following articles, and in this one we will focus on the main device that protects against the most dangerous and most common failures: overload and short circuit.

So, let's look at a high-quality device using the example of ABB circuit breakers.

What distinguishes a quality machine? It:

The actual ability of the electromagnetic release to withstand the short-circuit current of the required magnitude.

A certain thermal release cut-off time, i.e. clear match with the characteristics.

Both parameters are important in working conditions, but, unfortunately, it is possible to determine how strictly a certain device meets the standards only in laboratory conditions. And if you do not have such an opportunity, then there is only one way out — to buy products from proven brands from reliable distributors. There is also an opportunity to perform an autopsy and with an experienced eye determine the level of quality of the opened product.

Here is an example for comparison:

The main external differences

Original

Fake

Case details

High

low

Connecting additional contacts

there is

No

Bus connection above

there is

No

RosTest mark

there is

No

Interrupting capacity

4500

4000

Everyone should know this: UDPs are that simple

In our daily work, we often come across the fact that many of our partners would like to know more about RCD… For this modular device, the use of which is prescribed PUE, the only modular device that requires fire certification (with this we want to emphasize once again the importance of understanding the principles of its operation). We decided to try to fulfill this request. And before you contact us again about these products, we would like you to know about them what is written in this article.Our presentation, unfortunately, is overloaded with interesting information and we recommend that you read it as carefully as possible.

Many years ago, like many others, I firmly believed that the circuit breaker in the floorboard would save my life in the event of something. In general, this happened once: However, only later, conducting home experiments with the resistance of my own body, I became convinced that the machine is not a real protection against electric shock for a person, and that the circuit can be short-circuited by not all parts on the body. In other words, if a banal current of 16A at 220V flows through a person, then it will be enough for him.

This means that in order to truly protect a person from electric shock, you need a device that monitors the flow of current from the circuit (what will create the current flowing through the human body). Let us determine what magnitude of leakage current should be detected by such a device. For orientation, I give the following table.

Body current

Feeling

Result

0.5mA

It's not felt.

Safely

3 mA

Weak sensation with tongue, tips of fingers, across wound.

It is not dangerous

15 mA

Sensation close to an ant sting.

Unpleasant, but not dangerous.

40mA

If you have grabbed the driver, then the inability to let go. Body spasms, diaphragmatic spasms.

Choking hazard for several minutes.

80mA

Vibration of the heart chamber

Very dangerous, leads to a rather quick death.

The principle of operation of the RCD is quite simple and is based on two well-known physical laws: the rule for adding currents in a node and the law of induction. The operation of the RCD is schematically illustrated in the figure below.

The phase and neutral pass through the toroidal core, so the fields induced by them in the toroid are oppositely directed. Provided there are no leaks in the circuit, these fields cancel each other out. If a leakage occurs, as shown in the figure, current begins to flow in the winding of the toroid (since the currents flowing through neutral and phase are not equal). The magnitude of this current is estimated by the differential current relay «R». When a certain threshold is exceeded, the relay causes the circuit to break. Now let's touch on the differential current relay in more detail.

Its principle of action is also based on the law of induction. So, in a normal state, the "Armature" that drives the release is held in balance on one side by the field of a permanent magnet, on the other by a spring (indicated in the figure as force "F").

In case of leakage, the current induced in the toroidal coil passes through the differential current relay coil and induces a field in the core which compensates for the DC field of the relay magnet. As a result, force «F» actuates the release.

I want to note that such a relay has high sensitivity requirements. The differential current relay built into the ABB RCD has a sensitivity of 0.000025 W !!! Not all manufacturers can afford to integrate devices with such high sensitivity into their products. All other quality control elements must also be performed with high accuracy. So the photo on the right shows an ABB RCD, and on the left - another manufacturer (or rather a fake).
In the RCD in the figure on the left, a specific electronic unit is visible and the control signal to the release is provided by this particular unit. These.the principle of operation is not based on precise mechanics, but on electronics, and there is no accurate data to measure the reliability of such components.

As a result, RCDs built on the basis of such electronic blocks do not meet the requirements of the standards, although they work in certain situations (and their price is lower). And it's not even about the quality of the components of the electronic unit. In fact, in this case we are dealing with an RCD that depends on the supply voltage, for which, moreover, the protection is not guaranteed in the event of a break in the neutral.

And such RCDs are permitted only for special applications or in the case of permanent supervision of the equipment by trained personnel. But after all, the RCD is installed for this, so the probability of its operation in a certain situation is 100%, and not 80%or even 50%, as is the case with low-quality products, and some of them are completely inoperable . Remember that RCDs are installed mainly to protect children !!!

Now let's note a number of other points. In a row with classification, RCDs are subdivided On:

• Type AC — RCD, the shutdown of which is guaranteed in the event that the differential sinusoidal current appears either suddenly or slowly increases.
• Type A is an RCD, the opening of which is guaranteed in the event that a sinusoidal or pulsating differential current suddenly appears or slowly increases.

RCD type «A» is more expensive, but the scope of its possible application is greater than that of «AC» type. The fact is that the equipment, including the electronic components (computers, copiers, fax machines, ...), during of insulation breakdown to earth, can create non-sinusoidal but unidirectional, constant pulsating currents.

In this case, the change in inductance (dB1) caused by the pulsating direct current in the differential transformer (differential current relay) of the standard AC type is of low magnitude. This value is not sufficient to provide the necessary energy to open the breaker contacts. And in these cases, you should use an RCD of type «A». Its operation is achieved by a magnetic toroid with low residual inductance and an electronic circuit in the secondary winding of the transformer.

Of course, the material presented here is far from all that can be said about RCD. Follow our posts.