How does a fuse work? Which protective devices are better: fuses or circuit breakers? Protective characteristics of machines

a) Purpose of the fuse. Fuses appeared at the same time as electrical networks. Simplicity of device and maintenance, small size, high breaking capacity, low cost ensured their very wide application. LV fuses are manufactured for currents from mA to thousands of A and for voltages up to 660 V, and HV fuses - up to 35 kV and above.

Circuit breakers- these are electric devices designed to protect electrical circuits from current overloads and short-circuit currents.

Disconnection of the protected circuit occurs by destroying the live parts specially provided for this under the influence of a current exceeding a certain value.

In most structures, the circuit is disconnected by melting the fuse-link, which is heated directly by the circuit current. After disconnecting the circuit, it is necessary to replace the burned out insert with a serviceable one. This operation is carried out manually or automatically. In the latter case, the entire fuse is replaced.

The widespread use of fuses in various areas of the national economy and in everyday life has led to a variety of their designs. However, in spite of this, they all have the following basic elements: a housing or a support part, a fuse-link, a contact connection device, an arcing device or an arc-extinguishing medium.

b) The principle of the fuse, physical phenomena in an electrical apparatus. Disconnection of the protected circuit occurs through the destruction of live parts specially provided for this under the influence of a current exceeding a certain value.

In most structures, the circuit is disconnected by melting the fuse-link, which is heated directly by the current.

protected circuit. After disconnecting the circuit, it is necessary to replace the burnt-out insert with a serviceable one. This operation is carried out manually or automatically. In the latter case, the entire fuse is replaced.

At currents> I melting, the fuse must trip in accordance with the time-current characteristic. With the growth of the current, the degree of acceleration of the fuse-link burnout should increase much faster than the current. To achieve this characteristic, the insert is shaped or a metallurgical effect is used.

The insert is made in the form of a plate with cutouts (Fig. 6.1, a), decreasing its cross section in some areas. In these narrowed areas

Figure 6.1 - Temperature distribution ( a) and the place of burnout of figured fuse-links during overloads ( b) and at short circuit ( v)

more heat is emitted than on wide ones. At I However, the excess heat due to the thermal conductivity of the insert material has time to be distributed to wider parts and the entire insert has practically the same temperature. With overloads ( I ) heating of the constricted areas is faster, because only part of the heat has time to be removed to wide areas. The fusible link melts in one of the hottest places (Figure 6.1, b). At short circuit ( I » ) the heating of the constricted sections is so intense that practically the removal of heat from them can be neglected. The fusible link burns out simultaneously in all or several narrowed places (Figure 6.1, v).

In many designs, insert 1 is given such a shape (Figure 6.2, a), in which the electrodynamic forces F, arising at short-circuit currents, break the insert even before it has time to melt. In fig. 6.2, and the break point is indicated by a circle. This section is made with a smaller section.

Rice. 6.2. Examples of forms of fuse-links with their accelerated break

At overload currents, the electrodynamic forces are small and the fuse-link melts in the narrowed place. In the construction in fig. 6.2, b the acceleration of the circuit disconnection during overloads and short-circuits is achieved due to the spring 2, which breaks the insert 1 when the metal softens in the narrowed sections, before these sections melt.

The metallurgical effect is that many low-melting metals (tin, lead, etc.) are capable of dissolving other refractory metals (copper, silver, etc.) in the molten state. This phenomenon is used in fuses with parallel wire row inserts.

To accelerate the melting of the inserts during overloads, tin balls are soldered onto the wires. At overload currents, the ball melts and dissolves part of the metal on which it is soldered. The insert burns out at the place where the ball is soldered.

Fuse parameters

The fuse works in two sharp different modes: under normal conditions and conditions of overload and short circuit. In the first case, the overheating of the insert has the character of a steady-state process, in which all the heat released in it is released into the environment. In this case, in addition to the insert, all other parts of the fuse are heated to the established temperature. This temperature must not exceed the permissible values. The current for which the fuse-link is designed for long-term operation is called rated current of the fuse-link Inom. It may differ from the rated current of the fuse itself.

Typically, the same fuse can accommodate fuse-links for different rated currents. Fuse rating, indicated on it, is equal to the largest of the currents of the fuse-links intended for this fuse design.

The protective properties of the fuse during overload are standardized. For fuses of normal speed, the conventional non-melting current- current, when flowing for a certain time, the fuse-link should not burn out, conditional melting current- current, during which the fuse-link must burn out for a certain time. For example, for a fuse with fuse-links for rated currents of 63-100 A, the fuse-links must not burn out when a current of 1.3 I nom within one hour, and at a current of 1.6 I Nom should burn out in time up to one hour.

Consider the heating of the insert under continuous load.

The main characteristic of the fuse is time-current characteristic, representing the dependence of the melting time of the insert on the flowing current t= f ( i). For perfect protection, it is desirable that the time-current characteristic of the fuse (curve 1 in Fig. 6.3) at all points was slightly lower than the characteristics of the protected circuit or object (curve 2 in Fig. 6.3). However, the real characteristic of the fuse (curve

3) intersects curve 2. Let us explain this. If the characteristic of the fuse corresponds to curve 1, then it will blow due to aging or on starting.

Rice. 6.3. Coordination of the characteristics of the fuse and the protected object

engine. The circuit will trip if there are no impermissible overloads. Therefore, the fusing current of the insert is chosen to be higher than the rated load current. In this case, curves 2 and 3 intersect. In the area of large overloads (area B), the fuse protects the object. In area A, the fuse does not protect the object. At small overloads (1.5 - 2) I The heating of the fuse proceeds slowly. Most of the heat is given off to the environment,

The current at which the fuse-link burns out when it reaches a steady-state temperature is called boundary current I nogp. To prevent the fuse from blowing at rated current I no, it is necessary I noгp> I No. On the other hand, for better protection, the value I nogp should be as close to nominal as possible.

To reduce the melting point of the insert, low-melting metals and alloys (copper, silver, zinc, lead, aluminum) are used in its manufacture.

Consider the heating of the insert at short circuit.

If the current passing through the insert is 3 - 4 times higher I nom, then practically the heating process is adiabatic, i.e. all the heat generated by the insert goes to heating it.

Heating time of the insert to the melting point

where A "is a constant determined by the properties of the material; q- cross-section of the insert; j k is the current density of the insert.

As part of the fuse-link changes from solid to liquid, its resistivity will sharply increase (tenfold). Time of transition from solid to liquid

where is the resistivity of the insert material at the melting temperature; - resistivity of the insert material in the liquid state; y is the density of the insert material; L- latent heat of fusion of the material

The main parameter of the fuse in case of short circuit is breaking current limit- the current that it can switch off at a return voltage equal to the highest operating voltage.

The arc life depends on the fuse design. Total fuse disconnection time

t pr = t pl + t transition + t arcs

For fuse with insert in air

where the coefficient n= 3 takes into account the premature destruction of the insert, and k 0 = 1.2 -1.3 takes into account the duration of the arc burning.

In fuses with a filler (closed type), the destruction of the insert until it is completely melted is less likely. Fuse disconnection time

The coefficient k d = 1.7 -2 takes into account the duration of the arc burning.

Melting of the insert of variable cross-section occurs in the isthmuses with the smallest cross-section. The heating process proceeds so quickly that the heat almost does not have time to be removed to the areas of increased cross-section. The presence of isthmuses of a reduced cross-section allows to sharply reduce the time from the moment of the onset of the short circuit to the appearance of the arc. The process of extinguishing the arc begins before the short-circuit current reaches a steady or even amplitude value. An arc forms through time t 1 after the start of a short circuit, when the current in the circuit is much less than the steady-state value I k set

Arc extinguishing means allow the arc to be extinguished in milliseconds. In this case, the effect of current limitation is manifested, shown in Fig. When the damaged circuit with current limitation is disconnected, the arc extinguishing is facilitated, since it is not the steady-state short-circuit current that is disconnected, but the current determined by the melting time of the insert.

Rice. 6.4. Disconnection of DC and AC by a current-limiting fuse

Fuse design

c) Fuse device. Widespread use of fuses in

the most diverse areas of the national economy and in everyday life has led to a variety of their designs. However, in spite of this, they all have the following basic elements: a housing or a support part, a fuse-link, a contact connection device, an arcing device or an arc-extinguishing medium.

A fuse is an electrical switching device that is used to disconnect a protected circuit. Its purpose is to protect the electrical network and electrical equipment from short circuit and significant overload. The main parameters of the products are the rated and maximum breaking current, as well as the rated voltage. In this article, we will take a closer look at fuses: their purpose, types, device and principle of operation.

How does the device work?

The fuse operates in two modes, which are significantly different from each other.

Normal network mode. In this mode, the device is heated as a steady process. At the same time, it completely heats up to a certain temperature and gives off the released heat to the environment. The so-called rated current is indicated on each element (as a rule, it is indicated highest value current of a structural element). A fuse can be inserted into a fuse of different rated amperage.
Short circuit mode and. The device is designed so that with an increase in the current in the network, it could burn out in the shortest time. For this, the fusible element in some areas is made with a smaller section, where more heat is released than in wide areas. When almost all or completely all narrowed areas burn out. When an element melts, an electric arc is created around it, which is extinguished in the mechanism cartridge.

The strength of the current must be indicated on the body of the device, and also the maximum allowed voltage must be taken into account, at which the device will not fail.

The graph below shows the dependence of the burnout time of the fuse element on the current:

Where l10 is the current at which the element melts and disconnects it from the network in 10 s.

Varieties and types of elements

There are two types of fuses: low voltage and high voltage. This division is due to the magnitude of the voltage of the working electrical network in which the fuse is used.

Low-voltage devices are marked as PN or PR and are designed for voltages up to 1000 V. In low-voltage devices PN, there is a fine-grained filler around the copper insert. Their use is calculated up to 630 Amperes.

The PR device is simpler (in the photo below) than the PN, but with a short circuit and they are able to extinguish the electric arc. Designed for currents from 15 to 60 amperes.

By design features fuses are divided into cartridge, plug, plastic and tubular. By the type of execution, they produce collapsible and non-collapsible products. The collapsible ones have the ability to access the insert. The structure is disassembled and the burnt-out insert is replaced with a new one. Non-collapsible ones are constructed from a glass bulb, therefore, they are considered disposable and cannot be replaced.

Design

A modern fuse consists of two parts:

base made of electrical insulating material with metal thread (required for connection to the electrical circuit);
replaceable insert that melts.

The basis of the device is an insert that burns out or melts in the event of a short circuit. In order to extinguish the arc, which is formed as a result of the burnout of the replaceable insert, arc suppression devices are installed.

The leads of the insert are connected to the terminals in such a way that the fuse is connected to the line of the electrical circuit. For this, special reliable fastening clamps (holders) are used, which must ensure good contact. If it is not there, then heating may occur in this place.

A feature of the fuse design is that the device burns out before other parts of the mechanism are damaged. After all, it is easier to replace than a microcircuit or other piece of equipment. Therefore, such a part is chosen so that the rate of its melting is greater than in the wires of the line. Their temperature must not reach a dangerous level, as this will lead to equipment failure.

The design of the plug-type mechanism has the form of a cartridge, into which a fuse with a base is screwed. In the event of an emergency, the plug burns out. Today, this cork looks like a button similar to conventional switch... This button returns the device to working condition after an emergency.

In addition to protecting the electrical circuit from damage, the fusible component also protects against fires and flares. After all, an ordinary wire can come into contact with combustible materials at the time of fire, and the part burns out inside the device case.

The ratings of the device are selected according to the smallest rated currents of the electrical network or a separate part of the electrical circuit. The table of denominations is provided below:

If it is necessary to change such a component to AB ( circuit breakers), then their face value should be one step larger than the component part. For example:

We talked about that in the corresponding article.

Fuse- an electrical switching device designed to disconnect the protected circuit by destroying live parts specially provided for this under the influence of a current exceeding a certain value.

In most structures, the circuit is disconnected by melting the fuse-link, which is heated directly by the current of the protected circuit. After disconnecting the circuit, it is necessary to replace the burnt-out insert with a serviceable one.) This operation is performed manually or automatically. In the latter case, the entire fuse is replaced.

Rice. 5-1. Time-current characteristic of PN-2 series fuses

Fuses appeared at the same time as electrical networks. Simplicity of device and maintenance, small size, high breaking capacity, low cost ensured their very wide application. Low voltage fuses are manufactured for currents from milliamperes to thousands of amperes and for voltages up to 660 V, and high voltage fuses - up to 35 kV and above.

The widespread use of fuses in various areas of the national economy and in everyday life has led to a variety of their designs. However, in spite of this, they all have the following basic [elements: a housing or a bearing part, a fuse-link, a contact connection device, an arcing device or an arc-extinguishing medium.

The most important characteristic fuse is the dependence of the fuse-link burnout time on the current time-current characteristic (Fig. 5-1).

The fuse operates in two sharply different modes: under normal conditions and under overload and short circuit conditions. In the first case, the heating of the insert has the character of a steady process, in which all the heat released in it is released into the environment. In this case, in addition to the insert, all other parts of the fuse are heated to the established temperature. This temperature must not exceed the permissible values. The current for which the fuse-link is designed for long-term operation is called rated current of the fuse-link 1nom .. It can be different from the rated current of the fuse itself.

Typically, the same fuse can accommodate fuse-links for different rated currents. Fuse rating , indicated on it, is equal to the highest of the rated currents of the fuse-links intended for this fuse design.

The protective properties of the fuse during overload are standardized. For fuses of normal speed, the conventional non-melting current - current, during which the fuse-link should not burn out for a certain time, and conventional melting current - current, during the flow of which during the bonded time, the fuse-link must burn out. For example, for a fuse with fuse-links for rated currents of 63-100 A, the fuse-links must not burn out when a current of 1.3 In is flowed for one hour, and at a current of 1.6 In must burn out in up to one hour.

At currents exceeding the conventional melting current, the fuse must trip in accordance with the time-current characteristic. With an increase in the current, the degree of acceleration of the fuse-link burnout should increase much faster than the current. To obtain such a characteristic, the insert is given a special shape or a metallurgical effect is used.

The insert is made in the form of a plate with cutouts (Fig. 5-2, a), reducing its cross section in some areas. More heat is generated in these narrowed areas than in wide ones. At the rated current, the excess heat due to the thermal conductivity of the insert material has time to spread to wider parts, and the entire insert has practically the same temperature. With overloads (I≈I∞max), the heating of the narrowed sections is faster; since only part of the heat has time to be removed to wide areas. The fusible link melts in one of the hottest places (Fig. 5-2, b). In the case of a short circuit (I >> I∞), the heating of the narrowed sections is so intense that practically the removal of heat from them can be neglected. The fusible link burns out simultaneously in all or in several narrowed places (Fig. 5-2, c).

Rice. 5-2. Distribution of temperatures (a) and the place of burnout of figured fuse-links during overloads (b) and short circuits (c).

In many designs, the fuse-link 1 given such a shape (Fig. 5-3 a) in which the electrodynamic forces F, arising at short-circuit currents, break the insert even before it has time to melt. In the figure, the break point is indicated by a circle. This section is made with a smaller section. At overload currents, the electrodynamic forces are small and the fuse-link melts in the narrowed place. In the construction shown in fig. 5-3, b acceleration of circuit disconnection during overloads and short circuits is achieved due to the spring 2, tearing insert; when softening-metal in the narrowed areas before melting of these areas occurs.

The metallurgical effect is that many low-melting metals (tin, lead, etc.) are capable of dissolving some refractory metals (copper, silver, etc.) in the molten state. The solution obtained in this way has different characteristics than source materials(eg high electrical resistance and lower melting point) This phenomenon is used in fuses with inserts from a series of parallel wires.

Rice. 5-3. Examples of forms of fuse-links with their accelerated breaking.

To accelerate the melting of the insert during overloads and to reduce the overall temperature of the entire insert during its melting, small tin balls are soldered onto the wire. At overload currents, when the insert temperature reaches the melting point of tin, the ball melts and dissolves part of the metal on which it is soldered. There is a local increase in the resistance of the insert and a decrease in the melting point of the metal, in this place. The insert burns out in the place where the ball was fused. In this case, the temperature of the entire insert is much lower than the melting point of the metal from which it is made. In the nominal mode, the ball practically does not affect the heating temperature of the insert.

This method of obtaining the required time-current characteristic can be used with thin inserts, for example, with a ball diameter of 1 mm for wires with a diameter of 0.3 mm and a ball diameter of up to 2 mm for thicker wires. With an increase in the diameter of the insert, the influence of the metallurgical effect decreases sharply and practically does not affect it.

The considered methods of accelerating the burnout of the insert at overload currents and short circuits determine one very significant advantage of fuses - their current-limiting action. The fuse-link burns out much earlier than the current in the circuit during a short circuit manages to reach a steady-state value iset. Thus, the short-circuit current is limited by 2-5 times and thereby the destructive effect of electrodynamic forces is reduced. If, with a possible steady-state short-circuit current of 25 kA, the fuse-link burns out at 8 kA, then the value of the electrodynamic forces in the circuit is limited by more than 9 times. The current-limiting effect of fuse-links using the metallurgical effect is lower than with other methods of current limitation.

The extinguishing of the electric arc arising after the fuse-link burns out should be carried out as soon as possible. The time to extinguish the arc depends on the design of the fuse and the adopted method of extinguishing. The highest current that a fuse can turn off without any damage or deformation that impedes its further proper operation after replacing the fuse is called limiting breaking current fuse.

In modern fuses with closed cartridges without filler, the arc is extinguished due to the high pressure arising in the cartridge due to the appearance of an arc, and in the presence of a filler, due to intensive cooling of the arc by the filler and high pressure caused by the arc in the narrow channels of the filler. In this case, the arc is extinguished in a limited volume of the fuse holder. Neither arc flame nor ionized gases are emitted outside the cartridge.

A sufficiently perfect arc suppression system, together with the current-limiting action of the insert, determines the unlimited breaking capacity of the fuses. This does not mean that fuses can switch off arbitrarily large short-circuit currents. Unlimited breaking capacity should be understood as follows: fuses can be used to protect circuits in which the steady-state short-circuit current could reach very high values (in modern large power plants, 200-500 kA can be assumed). Fusible inserts are made of lead, lead-tin alloys, zinc, copper, silver, etc. Inserts made of low-melting metals (lead, zinc - melting temperature 200-420 ° C) allow to obtain a low temperature of the entire fuse, but they have low conductivity and are obtained significant cross-sections, especially at high rated currents. Zinc inserts are widespread. Zinc vapor has a relatively high ionization potential, which contributes to arc extinguishing. Inserts made of copper and silver are obtained with a smaller section, but their disadvantage is their high melting point, which, at overload currents, leads to strong heating and rapid destruction of the fuse parts. Copper fuse-links must be provided with an anti-corrosion coating. Otherwise, oxidation will lead to a gradual decrease in the section of the insert and untimely burnout.

The use of parallel fuse-links (at high currents) makes it possible, with the same total cross-section, to obtain a large cooling surface, thereby improving the cooling conditions of the inserts and better use the volume of the filler (in fuses with filler).

designed to protect individual devices and network sections from short-circuit currents and overload currents.

Usually fuses consist of a fuse holder and a fuse and differ in rated voltage and current. At a current higher than the rated one, the fuse-link burns out and opens the electrical circuit.

For protection power transformers for a voltage of 3 - 10 kV, PC fuses are used, in which a porcelain or glass cartridge is filled with quartz sand (see the figure below). Inside the cartridge there is a fusible link, designed for the passage of the rated current.

1 - porcelain cartridge. 2 - contact jaws,

3 - limiter. 4 - support insulator,

5 - base, 6 - lock

The PC fuses have sufficient breaking capacity - when the short-circuit current is cut off, the fuse does not break and there is no “ground” overlap and the adjacent elements of the installation do not occur.

At NS burnings fuse link The PC is triggered by a pointing device, which is located inside the cartridge and is held by a fusible link and a wire with a spring. When the fuse-link and the wire burn out, the spring is released and pushes the pointer outward. Insert the PC fuse holders into the holders' jaws so that the pointing device is at the bottom of the holder. The rated voltage and current of the fuse are indicated on the upper end part of the cartridge, for example: 10kV, 50A.

For mast transformer substations, outdoor quartz fuses PK-6N for a voltage of 6 kV and PK-10N for a voltage of 10 kV are used, which have sealed cartridges and support insulators designed for operation in the open air.

PKT-10 fuses are used to protect measuring transformers for voltages of 3 - 10 kV and, unlike PC fuses, do not have a signaling device.

To protect installations for voltages up to 1000V, use plug, tube and open (plate) fuses.

Plug fuse consists of a porcelain body and a plug with a fusible link. The supply line is connected to the fuse contact, the outgoing line to the screw thread. In the event of a short circuit or overload, the fuse burns out, and the current in the circuit stops. The following types of plug fuses are used: Ts-14 for current up to 10A and voltage 250V with a rectangular base; Ts-27 for a current up to 20A and a voltage of 500V with a rectangular or square base and Ts-33 for a current up to 60A and a voltage of 500V with a rectangular or square base.

Tubular fuses produce the following types: PR-2, PNN and PN-2. PR-2 fuses (collapsible fuse) are intended for installation in networks with a voltage of 500V and for currents of 15, 60, 100, 200, 400, 600 and 1000A.

1 - contact knives, 2 - brass caps,

3 - threaded sleeve, 4 - fiber tube,

5 - fusible link, 6 - screws

V fuse holder PR-2(see the figure above) the fusible insert 5, which is attached with screws 6 to the contact blades 1, is placed in a fiber tube 4, onto which threaded bushings 3 are mounted. Brass caps 2 are screwed onto them, securing the contact blades, which enter into fixed spring contacts installed on the insulating plate.

Under the influence of the electric arc that occurs when the fuse blows, the inner surface of the fiber tube decomposes and gases are formed, which contribute to the rapid extinguishing of the arc.

NPN fuses (bulk fuse non-collapsible) are manufactured for voltages up to 500V and currents from 15 to 60A, GSh-2 fuses (bulk fuse collapsible) - for voltages up to 500V and currents from 10 to 600A. V bulk fuses fusible links made of several parallel copper or silver-plated wires are placed in a closed porcelain cartridge filled with quartz sand, which facilitates rapid extinguishing of the electric arc.

Plate open fuses consist of copper or brass plates - lugs, into which copper calibrated wires are soldered. The terminals are bolted to the contacts on the insulators. Lamellar fuses with an open fusible link are used in the transformer substation of some city power grids and are replaced with closed PN-2, etc.

Fuses are used everywhere and everywhere - they are in technology, in a variety of electrical devices, cars, industrial equipment. There are many types of these elements. What are they for and what are their features? Consider the main types of fuses.

Characteristic

Fuse is a general term that has been used fairly consistently in the electrical field. This part assumes protection for wires, equipment and electrical networks.

The fuse is a switching product. What is its purpose? The fuse is meant to protect electrical network from high currents and short circuits. The principle of operation of the part is very simple - in the event of the formation of overcurrents, a specially designed element is destroyed. This is often a fusible link. This is how all types of glass fuses are arranged.

These inserts are an indispensable element, without which no type of safety elements is possible. There is also a special arc-extinguishing device inside it. Fuse inserts are made of porcelain or fiber housings and are fixed in special parts that conduct electric current. Elements designed for low currents may not have a housing at all.

Melting

These are the most common types of fuses for household use. Probably, this is the only element that is easiest to diagnose for serviceability. To do this, you just need to look at the detail in the light - it will be seen whether the fuse is intact or not.

These parts are made in a glass case.

Fusible tubular ceramic

This element is practically no different from a glass product. The only difference is in the material from which the case is made. But in operation, these parts are not so comfortable - it will no longer be possible to diagnose "into the light". For testing, you must use testers or multimeters.

Fuse insert LDPE

Fast acting fuses

These products are no different from the rest. The only difference is that when a short circuit occurs, the fusible part burns out very quickly.

SMD

These products can be found in electronic devices. They are very tiny. The principle of operation and purpose of fuses is to protect equipment from high currents, with which they do an excellent job.

Self-healing

These are quite interesting solutions. A self-healing fuse is a part with a special plastic inside. As long as the plastic insert is cold, it can conduct electricity. As soon as the insert heats up to a certain temperature, its conductive properties are lost due to an increase in resistance.

After cooling down, the current will be able to pass through the product again. The advantage of these parts is that after burnout there is no need to replace the element. The industry produces these products in various forms. They are suitable for surface or surface mount soldering. Basically, these types of fuses are used in low-power circuits.

Explosive

If everyone knows all of the above products, then the explosive fuse is a rare group. The burnout process of the part is provided with a rather effective sound. A special one that is attached to a conductive part explodes. Special sensors are responsible for this. The latter monitor the current in the electrical circuit. These are very accurate fuses, since they practically do not depend on the characteristics of the metal on the conductive part. This element depends on the accuracy of the current sensor.

Other types of fuses

To work in chains, special autogas, gas products, as well as liquid-type elements are used. There are even firing fuses. You cannot see them in everyday life - they are professional powerful equipment.

Marking and designations

Each manufacturer produces fuses under a specific code or article number. The fuse number allows you to find and clarify in catalogs specifications... These codes can often be found on product bodies. Also, the code can be applied to the metal part. In addition to codes, the main data can also be indicated on the case - these are rated current in A, rated voltages in V, tripping characteristics or design features. From this data, you can determine the purpose of the fuses.

So, the value of the rated current is the maximum allowable value at which the part can function normally for a long time.

Rated voltages are the maximum allowable voltage at which a part can safely break the circuit in the event of a short circuit or overload in the network.

Breaking capacity is called the maximum currents. With them, the fuse will work, but its body will not be destroyed.

The characteristics are called the dependence of the time at which the fuse collapses on the current that flows through the part. Different types of fuses according to their characteristics are combined into groups according to their application and response speed.

Usually these characteristics indicate the strength details. The letters of the Latin alphabet are used for designation. The first is the breaking capacity. So, G is the full range, the part is able to protect the circuit from both overload and short circuit. A - the range is partial, and these types of fuses only protect against short circuits.

The second letter indicates the types of chain: