A large range of electrical protection modules with different response characteristics makes it difficult to select the required model. Each parameter specified by the manufacturer must be taken into account correctly. Only in this case will your safety be ensured.
The article on the site provides a detailed overview of the operating characteristics of a differential machine with an explanation of the operating principle of each of them for a novice user. All you have to do is read them and put them into practice.
Safety is important
When designing and installing a low-voltage electrical network, one of the main tasks for specialists is protection against short circuits and ensuring the maximum level of safety.
To solve this problem, special devices are used, one of which is a differential automatic machine (difavtomat).
Below we will consider the following questions:
- What is this product?
- What are they used for, and what types of automatic machines are there?
- What elements does it consist of, and how does it work?
- How to decipher the symbols and connect the difavtomat?
- What are the reasons for the triggering?
Main settings
Any differential circuit breaker has 8 terminals for a three-phase network and 4 for a single-phase one. The device itself is modular and consists of:
- Housing made of non-flammable, refractory material;
- Terminals with markings intended for connecting conductors;
- On/off lever. The quantity depends on the model of the specific device;
- Test buttons, which allow you to manually check the operation of the differential machine;
- A signal light informing about the selected type of operation (leakage or overload).
Scope of application
The difavtomat is used to solve the following problems:
- Protection of a certain section of the network from the flow of increased currents that occur in the event of a short circuit or overload.
- Preventing fire or people being exposed to voltage due to leakage caused by poor-quality wire insulation or failure of household appliances.
In the first case, the differential circuit breaker operates as a circuit breaker, and in the second - as an RCD (residual current device).
What types are there?
A differential machine is a universal device that can be easily used in single- and three-phase networks.
In the first case, products with two poles are used, and in the second - with four.
Installation procedure
The RCBO is mounted on a DIN rail. When connecting, you need to be very careful not to confuse the order of connecting the cables. In household single-phase lines, the input conductor is connected to terminal number 1, and the output conductor is inserted into terminal number 2. The neutral wire is connected to the terminal marked with the letter N. Input cables are connected to the top of the device, and output cables to the bottom.
You can connect the outputs to the line directly. If the network parameters are not stable, or you want to ensure the highest level of protection, you should install additional AVs.
The neutral wires from the machines must be connected to an isolated neutral bus. To avoid failure of the device or its incorrect operation, it is necessary to ensure that the output neutral cable does not come into contact with other conductors or with the body of the electrical panel.
You can see how to connect the difavtomat in the video:
Design features, principle of operation and circuit diagram of the difavtomat
Considering the designation of a device according to GOST, it is easy to identify the structural elements of the protective device.
The main ones include:
- Differential transformer;
- Group of releases (thermal and electromagnetic).
Each element performs specific tasks. Let's take a closer look at them.
A differential transformer is a device with several windings, the number of which directly depends on the number of poles.
Its task is to compare the load currents in each of the conductors. If the indicators diverge, a leakage current appears, which is sent to the starting element.
If the parameter is above a certain level, the device turns off the electrical circuit by separating the power contacts of the difavtomat.
To test the functionality, a special button is provided, most often signed as “TEST”. It is connected through a resistor, which is connected in two ways:
- Parallel to one of the existing windings;
- Separate winding for the transformer.
After the button is triggered, the user artificially generates an unbalance current. If the difavtomat is working, it should turn off the circuit. Otherwise, conclusions are drawn about a malfunction of the device.
The next element of the automatic machine is the electric release. Structurally, it looks like an electric magnet with a core.
The purpose of the element is to influence the tripping mechanism. The electromagnet operates when the load current increases above the set level.
Most often this happens when a short circuit occurs in a low-voltage network. The peculiarity of the release is that it operates without a time delay. It takes a split second to turn off the power.
Unlike an electromagnetic one, a thermal release does not protect against short circuits in the circuit, but against overloads. The unit is based on a bimetallic plate through which the load current flows.
If it is higher than the permissible value (the rated current of the difavtomat), gradual deformation of this element occurs. At a certain point, the bimetal plate gradually bends.
At a certain moment it acts on the shutdown element of the protective device. The time delay of the thermal release depends on the current and temperature at the installation location. As a rule, this dependence is directly proportional.
The lower limit is written on the casing of the difavtomat (indicated in mA). In addition to the leakage current, the rated current of the release is also indicated. We'll talk about the device labeling in more detail below.
Short circuit protection
The main characteristic of RCBOs, thanks to which this device can protect circuits and consumers from short-circuit currents, is the so-called ultimate switching capacity (UCC). This is the maximum short circuit current that the switch can turn off and still remain operational. The most common PKS values are 3000, 4500 amperes. There are also devices that can withstand 6 or even 10 kA, but they are significantly more expensive because they require the use of expensive components.
How to decipher the symbols on the case?
It was already noted above that all the necessary information can be found on the body of the differential machine.
Having studied the basic parameters, it is easier to decide whether the device is suitable for solving specific problems.
The most important designations include:
- RCBO is an abbreviation, a shortened version of the full name (“residual current circuit breaker”).
- C25 - rated current parameter. Here C is the characteristic of the dependence of time and current, and 25 is the maximum current of the difavtomat, exceeding which is unacceptable.
- 230 V is the rated voltage at which the device can be used (for a household network).
- In 30mA—leakage current parameter. When 30 mA is reached, the RCD operates.
- A special sign that confirms the presence of the RCD function and the type of RCBO. Based on the presence of the designation, a conclusion is drawn about the ability of the differential machine to respond to direct or alternating pulsating current.
Also on the body of the protective product is a schematic diagram. It may not tell the average person anything, so there is no need to pay attention to it.
Also on the external part of the device there is a “TEST” button, which is necessary for periodic monitoring of the serviceability of the device in the RCD part. We have already discussed the features of checking using this element above.
Select the release characteristic of the machine: “B” or “C”
The most popular differential models have the following release characteristics: “B” is the most popular option. Characterized by minimal response delay. Suitable for domestic use in houses with old wiring. Not recommended for networks supplying equipment with high starting currents (washing machines, pumps, refrigerators, concrete mixers, etc.). Short-term excess loads provoke the so-called. false alarm. Instantly triggers at currents equal to 3-5 rated; “C” is a universal option, a good solution for private homes. It has a longer delay before operation, so it does not respond to high inrush currents. It is recommended to select for networks with a large accumulation of powerful electrical equipment running on electric motors. Instantly triggers at a load 5-10 times higher than the rated load.
Type “B” is best used for lines without powerful consumers, and type “C” is more suitable for outlet lines with a load of 1 kW or more.
To maintain selectivity, it is advisable to set “C” at the input, and “B” at the outlet lines and lighting, so that in case of short circuits the input differential does not operate before the group ones.
How to connect the device?
Before connecting the difavtomat, it is worth understanding the type of electrical wiring.
The following options are possible here:
- Network type - single-phase or three-phase. In the first case, the rated voltage will be 220 Volts, and in the second - 380.
- Availability of grounding - there are networks with or without grounding.
- Place for installation. Most often, RCBOs are installed in an apartment, but installation on each separate group of conductors is possible.
Taking into account the considered conditions, it is necessary to decide how to connect the protective device. It is worth remembering that a difavtomat may have a number of design differences.
Let's look at the main connection methods in the panel:
- The simplest option. A popular method is to install one differential circuit breaker that protects the entire chain. When choosing this option, it is advisable to buy a difavtomat with a high rated current in order to take into account the load of all consumers in the apartment. The main disadvantage of the scheme is the difficulty of finding the location of damage when the protection is triggered. In fact, the problem may be hidden in any of the wiring sections.
In the above diagram you can see that the “ground” comes separately and is combined with the ground bus. All conductors (PE) from electrical appliances are connected to it. The key is the connection of the “zero”, which is removed from the automatic machine. Its combination with other “nulls” of the electrical network is prohibited. This is explained by the difference in current values passing through each of the neutral conductors, which is why the differential machine can operate. - Reliable protection. This is an improved option for connecting a protective device, thanks to which it is possible to increase the reliability of the network and simplify the task of finding faults. The peculiarity is the installation of a separate difavtomat for each group of wires. Consequently, the protective device will only work in a situation where a problem occurs in the controlled section of the circuit. Other areas will continue to operate as normal. Unlike the previous scheme, it is much easier to find a fault in the event of a short circuit, leakage or overload in the network. But there is also a drawback - large financial costs associated with the need to purchase several automatic machines.
- Circuit without grounding. The options for connecting the difavtomat discussed above imply the presence of a protective “ground”. But in some houses or on a summer cottage there is no ground loop at all. In such networks, a single-phase network is used, where there is only a phase and a “zero”. In this situation, the protective device (AVDP) is connected according to a different principle.
If you also do not have a “ground” in your low-voltage network, it is advisable to completely change the wiring in the house before installing the difavtomat. Otherwise, there may be a leakage current in the network, which will trigger the RCD. - Scheme for 3-phase network. In cases where it is necessary to install a differential device in a three-phase circuit (for example, in a modern apartment, house or garage), an appropriate AVDP is required. The principle of construction here is the same as in the previous case. The difference is that four wires need to be connected at the input and output.
Complexity
Installation requires a certain number of minutes, and sometimes hours. Any designation on the diagram is clearly readable. One operation sometimes takes a long time. High-quality installation is always carried out using specialized tools - pliers, strippers and much more. This significantly saves your time.
If such equipment is not available, then it is better not to even start doing something yourself. It is better to give this work to a specialist; after all, we are dealing with an unsafe device for amateurs.
For what reasons can a difavtomat work?
When using a protective device, it is important to understand in what cases it may operate.
Taking these nuances into account, it is worth making a decision about the cause of the problem (short circuit, leakage current, etc.).
Let's look at each option in more detail:
Tripping without load.
Older homes with poor wiring have serious insulation problems.
The latter is worn out and there is a high risk of leakage currents, the magnitude of which can vary taking into account many parameters - the presence of nearby animals, humidity level, and so on.
In such a situation, the AVDP may trigger falsely.
The cause of the problem may be:
- Damaged insulation;
- Presence of twists;
- Miscalculations in the location of distribution boxes;
- Electrical accessories.
To identify the cause, a wiring audit is required. You need to start with diagnosing the location of the damage.
For example, if the automatic switch goes off when the light bulb is turned on, the problem must be looked for in the lighting circuit.
If the AVDP is triggered after connecting some device to the outlet, you should make sure that this device is working properly.
When the “zero” and “ground” are short-circuited.
If for any reason the N and PE wires touch each other, there is a high risk of the differential circuit breaker tripping. Common places for short circuits are in the electrical box or in the outlet box.
Read on the topic - effective ways to protect electrical appliances using special devices.
The triggering logic is based on the operating principle of the device. If neutral and ground are combined, the current is split between the two conductors. Accordingly, there is no equality of currents in the differential transformer, and it perceives this fact as a leak.
This problem is often encountered by novice craftsmen who do not have the proper experience in servicing the automatic machine.
- At the moment the load is turned on. If the AVDP operates when the load is connected, the problem must be looked for in the insulation. It is unsafe to use wiring with such a fault, so it is recommended to call a specialist and deal with the problem. If you ignore it, there is a high risk of one of your family members becoming energized or causing a fire.
- During voltage surges . The logic of the difavtomat is designed in such a way that a shutdown can occur in the event of an increase in voltage. True, not all devices have this option, but only those with an electronic circuit. In addition, the protection can work during a short circuit inside the consumer, because the automatic circuit breaker can turn off in this type of accident.
Read on the topic - how electric current acts on the human body.
Errors when purchasing
The main mistake when buying a automatic rifle is the desire to protect yourself. In this connection, consumers choose devices with minimal current protection and overload. As a result, numerous false positives are observed.
Exceeding the shutdown current does not guarantee reliable shutdown at high load currents.
Competent selection of automatic protection parameters is usually carried out by specialists, who also give recommendations on the distribution of electrical circuits and the installation of a power panel. The lack of proper qualifications does not guarantee normal protection of consumers from emergency situations.
