A circuit breaker is a specialized protection that allows you to protect electrical appliances from certain changes in direction. In fact, during normal operation of the system, this switch is considered a current conduction element. In the same case, if for some reason the current strength is more significant than the rated value, for example, if an electrical appliance malfunctions or if a short circuit occurs, a blur of circuits is formed in this switch, which prevents damage to other devices.
Today, automatic modular switches have become especially relevant, although quite recently they used ceramic plugs, which caused a very significant amount of inconvenience, since they were disposable. The new design has a lot of advantages, and the most important thing is that the circuit is disconnected, but the design itself remains in good condition, which means that it can be used many times.
The main function of these devices is to form a kind of protection element against possible system overloads or short circuits. In fact, the machine turns off at the moment when the parameters of the permissible load norm are significantly exceeded. Or when a short circuit occurs. There are situations when a sharp jump occurs in the network - an increase in electric current. In this case, a circuit shutdown is also formed, which causes the machine to shut down.
At the same time, the machine is always installed on the system, and accordingly, during normal operation of the system, it must carry out normal current conduction.
Why do you need a wiring machine?
Every person understands that the cost of modern equipment - a washing machine, refrigerator or iron - is quite significant, and it is for this reason that such elements must be reliably protected. An increase in the current value in the network can become the basis for the breakdown of such devices. So, it is the machine that is the main element of protection, since when the current level increases, it causes a shutdown of the entire electrical system, which in fact becomes the protection of all devices from the negative effects of high-power current.
But, if you dig deeper, the machine is designed to protect electrical wiring, not devices. If any wiring breakdowns occur, then opening the circuits becomes the main element of protection against many negative factors, including fires.
There are situations when the current in the network reaches several thousand amperes. In fact, no cable is capable of withstanding such a load for a significant amount of time. At the same time, it should be borne in mind that in wiring electricity in houses and apartments, a wire with a cross-section of 2.5 sq. mm is most often used, which, under such influence, can simply catch fire, which, as you understand, will cause a fire and an incredible number of difficulties.
Accordingly, it becomes clear that a circuit breaker is not a luxury, but a kind of necessity of our modern times, and the correct choice of this element of the electrical network is important.
Single-phase short circuits
In practice, single-phase short circuits occur in most cases. In networks with an isolated neutral, when one phase is connected to ground, the mode is not a short circuit and the uninterrupted power supply is not disrupted, but it must be turned off, since it corresponds to an emergency condition. When one phase is short-circuited to ground in a given network, the voltages on the other two phases increase by 1.73 times, and the voltage at the zero point becomes equal to the phase voltage relative to ground.
It will be interesting➡ What is electrolysis and where is it used in practice?
In networks with a solidly grounded neutral, when the wire is connected to the ground, a fuse burns or a circuit breaker trips, which disrupts the power supply, and if the fuse burns, the motor windings can be damaged when operating on two phases.
If in any part of the electrical wiring or electrical appliance (light bulb, iron, etc.) the insulation is broken and the phase wire touches the neutral wire, a short circuit will occur.
Since there is no load between the shorted wires, in other words, the electrical resistance of the contact point is practically zero, the current through the contact will begin to increase until the wires melt, which, in particular, can lead to a fire. Fuses are used to protect against short circuits.
A simple (in the form of a “plug”) fuse is a low-fusible insert included in the phase wire, which, when the current increases, will burn out and open the circuit long before more serious troubles occur. Structurally, the fuse is designed in such a way that this micro-disaster does not lead to damage to the fuse block. The little heroine who sacrificed herself is thrown out and replaced by the next one.
Modular circuit breakers
This is a unique, modern device that is provided today by many manufacturers. In such circuit breakers, two types of network releases are most often installed:
- A specialized thermal release that trips at the moment of overload. In fact, the design is equipped with a fairly high-quality bimetallic plate. When heated, due to the special qualities of the material, it straightens, which causes the chain to disengage. Note that depending on the amount of current supplied to the plate, its heating rate is formed. Accordingly, in this situation, the speed of operation of the machine will depend on the current strength that is passed through the plate;
- There is also an option for a magnetic circuit breaker. This element is triggered when short circuit currents arrive, which are not one-time, but multiple times exceed the established parameter standards.
What are the types
Short circuit. Everyone has heard this phrase. Many have seen the inscription “Do not short-circuit!” Often, when an electrical appliance breaks down, they say: “It’s short!” And despite the negative connotation of these words, professionals know that a short circuit is not a sad death sentence. Sometimes it is pointless to fight a short circuit (SC), and sometimes it is fundamentally impossible. This article will answer the most important questions: what is a short circuit and what types of short circuits are found in technology.
It will be interesting➡ What is a trigger in electronics - we understand the terms in detail
Let's begin to look at these issues from an unusual angle - we will find out in which cases short circuits are inevitable and where they do not play the role of damage. Let's take an ordinary metal wire at both ends. Let's connect the ends together. The wire is short-circuited - a short circuit has occurred. But since there are no sources of electrical energy or load in the circuit, such a short circuit does not cause any harm. In some areas of electrical engineering, the short circuit that we have considered plays into our hands, for example, in electrical devices and electrical machines.
Related material: How to connect a capacitor
Let's take a look at a single-phase relay or starter, the design of which includes a magnetic system with moving parts - an electromagnet that attracts an armature. Due to the constantly changing polarity of the current flowing in the windings of the electromagnet, its magnetic flux periodically becomes zero, which causes the armature to rattle, vibrations and a characteristic hum, familiar to all electricians, appear. To get rid of this phenomenon, a short-circuited turn - a ring or rectangle made of copper or aluminum - is attached to the end of the electromagnet core or armature.
Due to the phenomenon of electromagnetic induction, a current is created in the coil, creating its own magnetic flux, compensating for the loss of the main magnetic flux created by the electromagnet, which leads to a decrease or disappearance of vibrations that destroy the structure.
A short circuit in the rotor of an asynchronous electric motor also plays a role. Due to the interaction of the magnetic field created by the stator windings with the squirrel-cage rotor, according to the already mentioned law, currents appear in the rotor, creating their own field, which causes the rotor to rotate. Of course, it is important to properly design an electric motor or electrical apparatus so that the currents flowing in short-circuited elements do not lead to overheating and damage to the insulation of the main windings.
Socket fire
Similarly, the concept of "short circuit" is used in relation to transformers. People who are in one way or another connected with the energy industry know that one of the most important characteristics of a transformer is the short-circuit voltage, VSC, measured as a percentage. Let's take a transformer. We short-circuit one of its windings, say, low voltage (LV), with an ammeter, the resistance of which, as is known, is taken equal to zero. We connect the high voltage winding (HV) to a voltage source. We increase the voltage on the HV winding until the current in the LV winding becomes equal to the rated one, and fix this voltage.
We divide it by the rated voltage of the higher side, multiply by 100%, and get USC. This value characterizes the power loss in the transformer and its resistance, which determines the short circuit current leading to damage. Let's finally talk about short circuits that have negative consequences. Such short circuits occur when current from the power source does not flow through the load, but only through wires that have negligible resistance. For example, a three-phase cable is powered by a transformer, and with one careless movement of the excavator bucket it is damaged - two phases are short-circuited through the bucket. Such a short circuit is called two-phase. Other short circuits are called similarly based on the number of closed phases.
A single-phase earth fault in networks with an isolated neutral is not short, but can pose a threat to the lives of living beings. A short circuit in which the transition resistance is zero is called metallic - for example, with a bolted or welded connection. Short-circuit currents, depending on the voltage and type of damage, can reach thousands and hundreds of thousands of amperes, leading to fires and colossal electrodynamic forces that “twist” tires and wires. Protection against short circuits can be carried out by circuit breakers or fuses, and in high-voltage networks - by means of relay protection and automation.
Protection of the power supply from short circuit.
Short circuit protection (short circuit type)
The choice of a modular machine option begins with this aspect. You need to correctly calculate the current at the end of the line. The calculation process is considered quite complex, since it will directly depend on the following data:
- Transport type substation capacity;
- From the cross-section of the conductors used;
- From the length of the conductor, etc.
Many experts argue that an important aspect of choosing a machine is the correct design of networks. At the same time, when designing, the data determines that the most important parameter is the length of the line, that is, the cable that goes from the panel to the outlet or chandelier. It should immediately be noted that complex calculations can be eliminated, since in apartments, and even private houses, the length of the specified cable will be minimal. It is for this reason that the “C” class machine gun is most often chosen; the “B” option is used more rarely. However, this option is used exclusively for low-power lamps. As for using the machine in the kitchen, where the power of the appliances will be many times higher, then only class “C” is used. When using option “B”, a pattern of operation of the machine may be formed when the refrigerator or other device is turned on, since a jump in the starting current is formed.
- Options B3-5 are used to form protection against various active loads, but only with minimal aspects of energy consumption. Such machines are used for lighting;
- Options C 5-10 are intended to protect various circuits that have inductive and active loads. Such options are recommended for installation in residential and office premises;
- D 10-20 - automatic machines that are used when installing transformers (exclusively low-voltage), as well as when using lifting mechanisms or fairly powerful pumps;
- K 8-15 are intended for transformers and electric motors, there are also specialized options designed for high-quality electronics.
How to protect your home from short circuits
Modern electrical systems make human life and work more comfortable and convenient, but such networks can pose a danger to users and the electrical equipment connected to them. Among the most common electrical problems are short circuits that can occur during operation of the electrical system. Protection against short circuits is one of the most important tasks that designers need to solve in the process of preparing a power supply project for a house or apartment.
No electrical system is protected from the possibility of a short circuit. The cause of this problem can be any electrical device located inside the house. The owner should remember that among the most common causes of electrical overloads and short circuits is the use of household equipment for purposes other than their intended purpose. Even the highest quality electrical appliances can break down and pose a danger to users if they are not used as specified in the manufacturer's instructions. Proper use of devices can significantly reduce the risk of emergency situations, but it is impossible to completely eliminate such problems, therefore modern and high-quality protection devices must be installed in any electrical system.
Example of a draft technical report for a building
Back
Forward
Selection characteristics
There is a clear description of all the distinctive qualities and properties of such devices; accordingly, today you can make a rational, correct and competent choice by studying all the technical data of the device:
- A very important aspect of the choice is the triggering parameter from the defensive position;
- There is also such a thing as weight and size characteristics, which are taken into account when choosing a machine;
- Well, of course, you should pay attention to the installation characteristics.
The rated current data is indicated on the device body. In essence, data is generated that determines the time-current characteristic of the device. That is, at what current strength and for how long will this machine operate.
An equally important aspect is the operating voltage of the device. Almost all devices have a consumption of 220 V, however, the range of devices that are designed for protection in the form of automatic wiring have an operating voltage that is higher. This means that you need to choose a device that can match the operating voltage of the device. For example, for apartments and private houses, the 220 V option is selected (the data must be indicated on the body of the device). If we are talking about specialized equipment at an enterprise, then the data can be 230, 250, etc. Also, specialized markings are indicated on the body of the device, which determines what work the machine is intended for. Most often, such machines are used for alternating current.
When choosing a machine, you need to inquire about the number of poles. In fact, this characteristic determines the maximum number of possible devices that are connected to the machine. That is, this parameter determines the number of supply and protected wires or conductors that are turned off simultaneously when some non-standard situation occurs.
- Single-pole switches are typically used on a single-phase circuit. At the same time, they must be installed directly on the phase, which makes it possible to obtain prospects for protecting the lines extending from it. As a rule, such devices are used for lighting and socket lines;
- Three-pole options are intended for installation in a three-phase network, as an element of input circuit breakers.
A very important, but at the same time difficult to understand, characteristic is considered to be the time-current characteristic. Essentially, the data provided describes the dependence of the power of the current that flows through the circuit breaker, taking into account the time when the circuit breaker will operate, reacting to certain changes in the network. Note that the complexity of this characteristic lies in the fact that it will be necessary to use specialized graphs to carry out a correct and adequate calculation. This characteristic suggests that machines that have the same rating can be turned off differently, depending on the type of machine curve. Accordingly, based on this characteristic, it is possible to select an automatic type switch that will be designed for various types of load and will minimize the possibility of false alarms when certain devices are turned on.
It is also necessary to pay attention to the maximum short-circuit current. We partially examined this characteristic at the beginning of the article. As you understand, the parameter determines the maximum current at which the network is automatically turned off. The encoding of these parameters is indicated automatically. If you see a value of 6 kA, this means that at a current of 6000 amperes, the machine will carry out the process of opening and disconnecting the network. Accordingly, this parameter shows the maximum current at which the machine will open the contacts and there will be no power supply to the room.
Most often today you can find machines that have a characteristic of 4.5 kA, which in general is sufficient for standard premises in the form of private houses and apartments, since in household networks there is rarely a short circuit with higher value parameters. But, if you live in a room with outdated infrastructure, then you need to take an automatic machine with a higher value. There are also circuit breakers that open at 2 kA; they are considered obsolete and are not used in the design of electrical networks today.
The range of choices for this parameter is very significant. We also note that if the line that you want to protect is located close enough to the substation, then in this case the current supply can be very high, which is why you need to use a machine with values of 10 kA. Please note that as this parameter increases, the cost of the machine increases significantly. This means that you need to clearly define your needs so as not to pay more.
When choosing a machine, you need to take into account that its overall dimensions will also be significant, because you will need to correctly plan the location of these machines in the panel, and also choose a specialized panel to install all the machines that you plan for the room. It should be noted that almost all modular machines are quite small in size, which makes them very convenient to use.
Also study the installation specifications. There are specialized devices that are mounted on a DIN rail, and there are options for mounting on a specialized panel. You need to evaluate the advantages of both options in order to make the right choice before purchasing a machine, taking into account the simplicity and ease of installation specifically for your specific case.
Consequences of short circuits and ways to prevent them
A short circuit is characterized by the flow of increased current values. In turn, high current is dangerous for cables and connections. This is characterized by an avalanche-like development of the consequences of the circuit. The cables burn away from the connections, the connections themselves heat up, after which their accelerated destruction occurs. Heating may cause electrical wiring to ignite and cause a fire.
To prevent the consequences of phase-to-phase faults in 220/380 circuits, fuses, fuses, and circuit breakers are used. Fuses, when a current higher than the rated current flows through them, burn out, thereby breaking the circuit. After replacing the fuse, if you have not eliminated the phase-to-phase short circuit, it will burn out again and again.
To improve working and operating conditions and eliminate the need to replace fusible elements, automatic switches are used. They react both to a slight increase in current above normal (thermal release) and to a sharp, strong increase (electromagnetic release). In the event of a fault between phases or between phase and earth, the circuit breaker will trip. In such cases they say “the machine was knocked out.” To restore the voltage supply, you must re-cock the machine lever or switch the button (on AP-shkas).
The video clearly shows the danger of an interphase short circuit (a mannequin was hit, these were demonstration performances):
https://youtube.com/watch?v=HFhNHFDz2cc
Power parameters
Probably, this parameter needs to be considered in more depth, since it is of the most important importance. To correctly calculate this power, you need to draw up a project. All devices and fixtures that will be located in the room are taken into account. The most correct way to determine the current of an electrical receiver is to use the current value data from the nameplate, or from the device passport.
The nameplate is on almost all electrical devices and equipment. In this situation, you need to study the provided data in detail in order to correctly calculate the power of the machine that you will need to install in a particular room.
For example, the calculation of the socket line can be determined by a kind of summation of the current of all electrical receivers that are in a particular room. Based on the calculated values, you will need to select the appropriate rating of the circuit breaker. If the total value shows 4.06 A, then you will need to purchase a 6 A machine.
Please note that it is impossible to select a circuit breaker solely based on power parameters. It is also necessary to take into account aspects of the cross-sectional values of the wire and cable, as well as all the other characteristics that we listed above.
Causes
A short circuit in the electrical network occurs when the current increases sharply, which in turn increases when the wiring resistance decreases. As a result, the increased current creates critical temperature values, which will result in the ignition of all flammable materials, including core insulation.
The reasons why short-circuit current occurs are primarily:
- Network aging. The insulating layer wears out over time and breaks form at the bend points, where the contact is exposed.
- Flooding by neighbors resulting in moisture deteriorates the sticky side of the tape that protects the twist.
- Mechanical damage to core insulation. For example, if you drive a nail directly into the cable location. That is why it is recommended to initially find the wire in the wall, and then proceed to construction work.
- The negative effect of rats that sacrifice their lives and simply chew the cable. In this case, you can avoid danger by taking measures to protect the wiring from rodents.
- Prolonged network overload, which leads to melting of the insulating layer.
- Failure of an electrical appliance, which in turn short-circuits the electrical circuit.
Simply put, if two bare wires of different poles come into contact (phase and zero), a sharp increase in temperature will occur and further adverse consequences of a short circuit, which we will talk about later.
Wire size
There are certain fire safety requirements that determine all the nuances of choosing a machine for electrical wiring, taking into account the wire cross-section. Note that a single-phase network is used for lighting and sockets, and it has a voltage of 220 V. At the same time, if separate networks are formed that determine the presence of power transmission lines passing along the street, then in this case a voltage of 380 V is formed.
There is a developed table in which you can find a description of the value of the continuous permissible current for various conductors with different cross-sections. The parameters of the machine are also selected to match the given wire cross-section.
Number of machines
To install a machine, a specialized distribution panel is installed, and machines are installed in it. A separate machine is installed on the outlet lines, taking into account one machine for several rooms. It is best to install the machines separately on lighting lines, and experts recommend installing one machine per room. Also, each powerful device that consumes electricity has its own automatic machine installed separately.
How to make the right choice?
When choosing a machine, you must take into account the cross-section of the wires, as well as the load that will be on the line. You definitely need to carefully evaluate the options provided, taking into account the relevance of certain manufacturers. Try to purchase such devices only in specialized stores, and be sure to check the quality certificates for the products.
The range of offers in the form of slot machines today has become quite significant. In principle, you will not have any particular difficulties when choosing and calculating such devices if you contact specialists who will draw up the electrical network project. But if you carry out all the actions yourself, use our recommendations for choosing devices that will reliably protect your premises from fire, and your devices from damage.
