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 circuits and significant overloads. The main parameters of the products are the rated and maximum switchable current, as well as the rated voltage. In this article we will take a detailed look at fuses: their purpose, types, design and principle of operation.
How does the device work?
The fuse operates in two modes, which differ significantly from each other.
- Normal network mode. In this mode, the device heats up as a steady process. At the same time, it completely heats up to a certain temperature and releases the generated heat to the environment. The so-called rated current strength is indicated on each element (as a rule, the largest current value of the structural element is indicated). The fuse can accommodate a fuse element of different rated current.
- Short circuit mode and . The device is designed in such a way that if the current in the network increases, it could burn out in the shortest possible time. To do this, the fusible element in certain areas is made with a smaller cross-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’s socket.
The current strength must be indicated on the device body, and the maximum permitted voltage at which the device will not fail must also be taken into account.
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 is disconnected from the network in 10 s.
Varieties and types of elements
Fuses are divided into two types: low voltage and high voltage. This division is explained by the voltage value of the working electrical network in which the fuse is used.
Low-voltage devices are labeled as PN or PR and are designed for voltages up to 1000 V. In low-voltage PN devices, there is a fine-grained filler around the copper insert. Their use is designed up to 630 Amperes.
The PR device is simpler (pictured below) than the PN, but in the event of a short circuit, they are also capable of extinguishing an electric arc. Designed for currents from 15 to 60 Amps.
Based on their design features, fuses are divided into cartridge, plug, plastic and tubular. Depending on the type of execution, collapsible and non-dismountable products are produced. Collapsible ones have the ability to access the insert. The structure is disassembled and the burnt insert is replaced with a new one. Non-separable ones are constructed from a glass bulb, therefore they are considered disposable and the inserts cannot be replaced.
Design
A modern fuse consists of two parts:
- a base made of electrical insulating material with metal threads (necessary for connection to an electrical circuit);
- replaceable insert that melts.
The basis of the device is an insert that burns or melts during a short circuit. In order to extinguish the arc that is formed as a result of the burnout of the replaceable insert, arc extinguishing devices are installed.
The terminals of the insert are connected to the terminals in such a way that the fuse is connected to the electrical circuit line. For this purpose, special reliable fastening terminals (holders) are used, which must ensure good contact. If it is not there, then heating may occur in this place.
A design feature of fuses 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 hardware component. Therefore, such a part is selected so that its melting rate is greater than in the line wires. Their temperature should not reach dangerous levels, 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. When an emergency occurs, the plug burns out. Today this plug looks like a button, similar to a regular switch. This button returns the device to working condition after an accident.
In addition to the fact that the fusible component protects the electrical circuit from damage, it also protects against fires and fires. After all, an ordinary wire can come into contact with flammable materials at the moment of fire, and the part burns inside the device body.
The device ratings are selected based on the lowest calculated 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 replace such a component with AB (circuit breakers), then their rating should be one step greater than the component part. For example:
We talked about this in the corresponding article.
Fuse is an installation product designed to protect electrical appliances by cutting off the supply of electricity to them when the permissible current value is exceeded by melting the calibrated wire installed in the fuse.
To protect electrical wiring and expensive radio equipment from short circuits, current surges in the supply network and ensure the safe operation of electrical appliances, fuses are widely used. They are produced in different designs, standard sizes and for any protection currents.
The considered fuse repair technology, if all conditions are met, will ensure its protective function. But not everyone has experience working with a soldering iron and measuring wire diameter. And in any case, an industrial fuse will work more reliably.
Previously, apartment electrical wiring was also protected exclusively with the help of fuses installed in plugs. Currently, more reliable reusable short circuit protection devices are used to protect electrical wiring - circuit breakers. In electrical appliances, nothing better protection against short circuits than a fuse has yet been invented. The use of fuses in cars is especially important, since they are the only reliable and cheap means of protection against short circuits.
Conventional graphic symbol
fuse
The conventional graphic designation of a fuse in the diagrams is similar to the designation of resistance, and differs only in that the line passes through the middle of the rectangle without breaking. Next to the symbol, the letter Pr is usually written. or F. Sometimes the diagrams simply write thermal fuse or fuse. After the letter, the protection current of the fuse is often indicated, for example F 1 A, means that the circuit has a fuse for a protection current of 1 ampere.
During operation, fuses fail and have to be replaced with new ones. It is believed that fuses cannot be repaired. But if you approach the repair process competently, then almost any fuse can be successfully repaired and reused. After all, the fuse body remains intact, and only a thin calibrated wire located inside the body burns out. If the burnt wire is replaced with the same one, the fuse will continue to serve.
How the fuse works in the video
When an electric current passes less than the maximum permissible, the calibrated wire connecting the fuse contacts heats up to a temperature of about 70˚C. If the current exceeds the fuse rating, the wire begins to heat up more strongly and when the melting temperature of the metal from which it is made is reached, it melts, the electrical circuit breaks, and the flow of current stops.
That's why the fuse is called a fuse or fusible link. The video is presented in slow motion so that you can clearly see how the wire in the fuse burns out. In real conditions, the wire in the fuse burns out almost instantly.
The fuse protects against excess current in the circuit and the voltage of the supply network in which it is installed does not matter, it can be a 1.5 V battery, a 12 V or 24 V car battery, a 220 V AC network, a three-phase network 380 V. That is, you can install the same fuse, for example, with a rating of 1 A, both in the fuse block of a car, and in a flashlight and in a 380 V switchboard. All types of fuses differ only in appearance and design, and work on the same principle - when exceeded of a given current in the circuit, the wire in the fuse melts due to heating.
There are two main reasons for fuse failure, due to surges in the supply voltage or a breakdown inside the radio equipment itself. Rarely, fuse failures also occur due to poor quality.
Many people think that the fuse cannot be repaired. But it is not so. In an emergency situation, when there is no spare at hand and, for example, because a car on the road or an amplifier refuses to work, and the musical accompaniment of a school ball or wedding is disrupted, and all the shops are already closed, there is no choice.
With the right approach, you can successfully restore a blown fuse for temporary use until it is replaced with a new one, preserving its protective functions. Often such problems are solved by simply closing the contacts of the fuse holder with any available wire, or even worse, simply inserting a nail or a piece of thick wire instead of the fuse. Such a decision can completely ruin everything and contribute to a fire.
Fuse Types
According to their purpose and design, fuses are of the following types:
- Plugs (mainly used to protect electrical wiring and devices in cars);
- With low-current inserts to protect electrical appliances with current consumption up to 6 amperes;
- Cork (installed in panels of residential buildings, designed for protection current up to 63 amperes);
- Knife type (used in industry to protect networks with current consumption up to 1250 amperes);
- Gas generating;
- Quartz.
The repair technology discussed in the article is intended for restoring fork fuses, with low-current inserts, plug and blade type fuses.
Tubular fuses
A fuse of a tubular design is a glass or ceramic tube, closed at the ends with metal caps, which are connected to each other by a wire of calibrated diameter running inside the tube. You can see the appearance of tubular fuses in the photograph.
The wire is spot welded to the caps or soldered with solder. In fuses designed for very high currents, the cavity inside the tube is often filled with quartz sand.
Automotive fuses
Fuses in cars rarely fail. Usually only in cases where the equipment fails. Most often when the headlight bulbs burn out. The fact is that when the filament of a light bulb breaks, a Voltaic arc is formed, the filament burns out and becomes shorter, the resistance sharply decreases and the current increases many times over.
It happens that a fuse in a car burns out when the windshield wipers jam. Less often during short circuits in electrical wiring. In the photo you see widely used automotive blade (fork) type fuses. Below each fuse is the current of its protection in amperes.
A blown fuse in a car should be replaced with a fuse of the same rating, but it can also be repaired by replacing the blown wire in the fuse with a copper wire of the appropriate diameter. The voltage of the car's on-board network does not matter. The main thing is the correspondence of the protection current. If it is difficult to determine the rating of a blown car fuse, then you can use color coding.
Color coding of automotive fuses
Formula for calculating fuse wire diameter
according to the power of the electrical appliance
Power is often indicated on labels affixed to products. If the power consumption is indicated on the product, then the rated current of the fuse can be calculated using the formula below.
Where I nom – rated fuse protection current, A; P max – maximum load power, W; U– supply voltage, V. But it is much more convenient to use ready-made data from tables. Please note that the first table is used to select the fuse rating of products powered from a 220 V household power supply, and the second table is for products used in cars with an on-board voltage of 12 V.
Table for selecting the fuse rating depending on the power consumption of the electrical appliance at a supply voltage of 220 V
Let's look at an example of how to choose a fuse.
The TV stopped working after a thunderstorm. It has been determined that the fuse has blown. Its denomination is not known. On the back cover label it is written that the power consumption is 120 W, sometimes it is written as 120 VA. This is a designation of the same power, but according to the standards of different countries. According to the table, it turns out that for electrical appliances with a maximum power consumption of 120 W (the closest value is 150 W) there is a 1 A fuse.
The method for selecting a fuse to protect the on-board electrical wiring of a car is no different from the choice for 220 V household electrical wiring.
Table for selecting the fuse rating depending on the power consumption of the electrical appliance at a supply voltage of 12 V (vehicle on-board network)
If after two replacements the fuses blow out each time, it means that the electrical appliance is damaged and requires repair. An attempt to set a fuse to a higher current can only cause further damage to the product, even to the point of being beyond repair.
Fuse current calculator
If the tables do not contain data for your case, for example, the supply voltage of the product is 24 V or 110 V, then you can perform the calculation yourself using the online calculator below.
When calculating on a calculator you will get the exact current value. For reliable operation of the fuse, its rating must be at least 5% higher. For example, if a calculated current value of 1 A is obtained, then you need to take a fuse of the highest closest rating from the standard range, that is, 2 A.
Sometimes attempts to determine the fuse rating by reading the information do not work. There are no inscriptions on the electrical device; the markings on the fuse are unreadable. If you have an ammeter and experience working with it, then by removing the fuse and connecting the ammeter to the contacts of the block in which the fuse was installed, you can measure the current and thereby determine its rating.
But there is a pitfall here. If the fuse fails due to a malfunction of an electrical device, then the current may be much greater than it should be, in addition, the measuring device may also be damaged.
Calculation of fuse wire diameter
To repair the fuse, it is necessary to replace the burnt wire. In the production of fuses in factories, depending on the current value and speed, calibrated silver, copper, aluminum, nickel, tin, lead and wires made of other metals are used.
For making a fuse at home, only red copper of calibrated diameter is available. All electrical wires are made of copper, and the more elastic the wire, the thinner the conductors and the greater the number of them. Therefore, all the technology proposed below is focused on the use of copper wire.
When choosing a fuse for equipment, developers use a simple law. The fuse current must be greater than the maximum consumed by the product. For example, if the maximum current consumption of the amplifier is 5 amperes, then the fuse is selected at 10 amperes. The first thing you need to do is find its marking on the fuse body, from which you can find out what current it is designed for. Often the current value is written on the product body, next to the location where the fuse is installed. Then, from the table below, determine what diameter wire is needed.
Tables for choosing wire diameter
depending on fuse protection current
For repairing fuses with protection current from 0.25 to 50 amperes
| 0,25 | 0.5 | 1.0 | 2.0 | 3.0 | 5.0 | 7.0 | 10.0 | 15.0 | 20.0 | 25.0 | 30.0 | 35.0 | 40.0 | 45.0 | 50.0 | ||
| Wire diameter, mm | Copper | 0.02 | 0.03 | 0.05 | 0.09 | 0.11 | 0.16 | 0.20 | 0.25 | 0.33 | 0.40 | 0.46 | 0.52 | 0.58 | 0.63 | 0.68 | 0.73 |
| Aluminum | - | - | 0.07 | 0.10 | 0.14 | 0.19 | 0.25 | 0.30 | 0.40 | 0.48 | 0.56 | 0.64 | 0.70 | 0.77 | 0.83 | 0.89 | |
| Steel | - | - | 0.32 | 0.20 | 0.25 | 0.35 | 0.45 | 0.55 | 0.72 | 0.87 | 1.00 | 1.15 | 1.26 | 1.38 | 1.50 | 1.60 | |
| Tin | - | - | 0.18 | 0.28 | 0.38 | 0.53 | 0.66 | 0.85 | 1.02 | 1.33 | 1.56 | 1.77 | 1.95 | 2.14 | 2.30 | 2.45 | |
For repairing fuses with protection currents from 60 to 300 Amps
| Fuse protection current, Ampere | 60 | 70 | 80 | 90 | 100 | 120 | 160 | 180 | 200 | 225 | 250 | 275 | 300 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wire diameter, mm | Copper | 0.83 | 0.91 | 1.00 | 1.08 | 1.16 | 1.31 | 1.59 | 1.72 | 1.84 | 1.99 | 2.14 | 2.28 | 2.41 |
| Aluminum | 1.00 | 1.10 | 1.22 | 1.32 | 1.42 | 1.60 | 1.94 | 2.10 | 2.25 | 2.45 | 2.60 | 2.80 | 2.95 | |
| Steel | 1.80 | 2.00 | 2.20 | 2.38 | 2.55 | 2.85 | 3.20 | 3.70 | 4.05 | 4.40 | 4.70 | 5.0 | 5.30 | |
| Tin | 2.80 | 3.10 | 3.40 | 3.65 | 3.90 | 4.45 | 4.90 | 5.80 | 6.20 | 6.75 | 7.25 | 7.70 | 8.20 | |
Formula for calculating the diameter of copper wire
for fuse
To determine more accurate values for the diameter of a copper wire to repair a fuse, or if a fuse is required for a protection current whose value is not in the table, you can use the formula below.
Where I pr – fuse protection current, A; d– diameter of copper wire, mm. How to measure wire diameter
The diameter of a thin wire is best measured with a micrometer. If you don’t have a micrometer at hand to measure the diameter of the wire, you can use an ordinary ruler.
You need to wind 10-20 turns per turn of wire on a ruler, divide the number of closed millimeters by the number of wound turns. Get the diameter. For example, I wound 10 turns of wire and they covered 6.5 mm. Divide 6.5 by 10. The diameter of the wire is equal to 0.65 mm. 0.05 mm is occupied by insulation. Therefore, the actual diameter is 0.6 mm.
Such a wire is suitable for making a 30 A fuse. The wire was wound thick for greater clarity. The more turns you wind on the ruler, the more accurate the measurement result will be. You need to wind at least one centimeter. If you have a short length of wire, then wind it around any rod, for example, a screwdriver, toothpick or pencil, and measure the width of the winding with a ruler.
You can process the measurement results using an online calculator. To determine the diameter of the wire, just enter the winding width, the number of turns in the windows and click “Calculate wire diameter”.
DIY fuse repair
Tube fuse repair
The first one is the simplest. The wire is stripped to a shine and wound several turns onto each cup, then the fuse is inserted into the holder. This method is not reliable and can only be used as a temporary measure. Due to its simplicity, it allows you to quickly check the serviceability of an electrical appliance. If the wire melts when turned on, it means the fuse is not the problem and more qualified repairs are required.
The second method is somewhat more complicated. But it also does not require soldering. You need to warm up the cups one by one with a lighter or on a gas stove and, holding them through the cloth with your hands, remove them from the glass tube. You can also heat it with a soldering iron. To ensure good contact, the inside of the cup must be thoroughly cleaned of any glue residue.
Pass the wire stripped of insulation through the tube diagonally, bend its ends along the tube and put the cups in place. The fuse has been repaired.
The third method is essentially the same as the first two. But a repaired fuse is practically no different from a new one. The repair is carried out as follows.
When making a fuse, factory calibrated wire is threaded through the holes in the ends of the cups and fixed with solder. In order to insert a new wire, you need to heat the ends of the cups with a soldering iron and use a toothpick or a sharpened wooden stick to free the holes in the ends of the cups from solder. Next, perform the factory operation described above.
There are holes in cups of very small diameter and it is difficult to clean them from solder. Then, if technically possible, it is easier to drill holes with a drill with a diameter of 1-2 mm or widen them with a faceted awl
The proposed technology for repairing fuses and fuse links can be successfully used to restore almost any type of fuses.
Blade type car fuse repair
The technology for repairing a car fuse is no different from the technology for repairing a tubular fuse; it is even simpler, since there is no need to disassemble it.
First, you need to use sandpaper or a file to clean the fuse blades at its base with a strip of a few millimeters and tin these places with solder.
When tinning, I encountered the fact that when using alcohol-rosin flux, the solder did not want to spread over the surface of the knives. I had to use FIM flux, intended for soldering copper, silver, constantan, platinum and ferrous metals. The basis of the flux is phosphoric acid. I always use it for soldering if rosin is not suitable. Residues of FIM flux are removed by washing with water.
The fuse was designed for a protection current of 10 A, therefore, in accordance with the table above, a wire ⌀0.25 mm was taken for repair. The wire was shaped into a loop, as shown in the photo, and its ends were tinned with solder.
After all the preparatory work, all that remains is to insert the wire loop inside the fuse housing and solder the ends to the legs.
Spread solder can be cut off with a knife, removed with sandpaper, or filed off with a file.
The car fuse has been repaired and can now be reused to protect circuits in the car's electrical wiring. If, after installing the repaired fuse, it blows again, then you need to look for a fault in the vehicle’s electrical equipment.
How to make a blown fuse indicator with your own hands
There are car fuses on sale with a fault indicator. A miniature incandescent light bulb or LED is built into the fuse housing, which begins to glow when the fuse blows. You can assemble such a blown auto fuse indicator with your own hands using the electrical diagram shown in the photo below.
To do this, it is enough to connect in parallel to the fuse contacts, any LED VD1 through a current-limiting resistor R1 or a miniature light bulb rated for a voltage of 12 V. The fuse blown indicator can be mounted either in the fuse body or installed on the block of its holder. The second option is preferable, since when replacing the fuse, the indicator will remain in place. The indicator will not light if the fuse is blown and there is no load connected.
The circuit shown in the photograph indicating that a fuse has blown or a circuit breaker has tripped can also work successfully in a household electrical network with a supply voltage of 220 V.
It is enough to increase the value of resistor R1 to 300-500 kOhm and to protect the LED VD1 from breakdown by reverse voltage, supplement the circuit with a diode VD2 of any type, designed for a reverse voltage of at least 300 V. For example, the widely used domestic diode KD109B or imported 1N4004 will do.
For a 220 V AC network, you can make a fuse or circuit breaker blown indicator on a neon light bulb.
When operating a household and industrial electrical network, there is always a risk of electrical injury or equipment damage. They can occur at any time when critical conditions appear. Protective devices can reduce such consequences. Their use significantly increases the safety of using electricity.
Electrical circuit protections operate on the basis of:
fuse;
mechanical circuit breaker.
Operating principle and fuse design
Two brilliant scientists, Joule and Lenz, simultaneously established the laws of mutual relationships between the amount of current passing in a conductor and the release of heat from it, revealing the dependence on the resistance of the circuit and the duration of the period of time.
Their findings made it possible to create the simplest protective structures based on the thermal effect of current on the metal wire. It uses a thin metal insert through which the full current of the circuit is passed.
At rated parameters for transmitting electricity, this “wire” reliably withstands the thermal load, and if its values exceed the norm, it burns out, breaking the circuit and relieving the voltage from consumers. To restore the functionality of the circuit, it is necessary to replace the burnt-out element: the fuse-link.
It is clearly visible on the designs of fuses for household television and radio equipment with glass, transparent insert housings.
Special metal pads are mounted at its ends, creating electrical contact when installed in the sockets. This principle is embodied in electrical plugs with fusible links, which for many decades protected our parents and older generations from damage in electrical wiring.
Automatic structures were developed using the same form, which were screwed into sockets instead of plugs. But when triggered, they did not require replacement of components. To restore power supply, simply push the button inside the case.
Old electrical connections to the apartment were protected in this way. Then, along with fuses, they began to appear.
The choice of fuse is based on:
rated current values of the fuse itself and its insert;
coefficients of minimum/maximum test current multiplicity;
limit switchable electric current and the possibility of interruption of transported power;
protective characteristics of the fuse link;
fuse rated voltage;
compliance with the principles of selectivity.
The fuses have a simple design. They are widely used in electrical installations, including high-voltage equipment up to 10 kV, for example, in the protection of voltage instrument transformers.
Operating principle and design of the circuit breaker
The purpose of a mechanical switching device called a circuit breaker is:
turning on, passing, turning off currents in normal circuit mode;
automatic removal of voltage from an electrical installation during emergency conditions, for example, metal short circuit currents. Circuit breakers operate in reusable short circuit and overload protection modes. The possibility of repeated use is considered their main difference from a fuse.
During the Soviet era, automatic circuit breakers of the AP-50, AK-50, AK-63, and AO-15 series were widely used in the energy sector.
Modern electrical circuits use improved designs from foreign and domestic manufacturers.
All of them are enclosed in dielectric housings and have common executive bodies that provide:
1. thermal tripping of the circuit when the permissible current value is slightly exceeded;
2. electromagnetic cut-off during sudden load surges;
3. arc suppression chambers;
4. contact systems.
In the case of heating by the energy of the generated heat, a bimetallic plate works, bending under the influence of temperature until the release mechanism is activated. This function depends on the amount of heat released and is extended over time until a certain point.
The cut-off operates as quickly as possible from the operation of the electromagnetic solenoid with the occurrence of an electric arc. To extinguish it, special measures are used.
Reinforced contacts are designed to withstand repeated breaks.
Operational differences between circuit breakers and fuses
The protective properties of both methods have been time-tested, and each method requires an analysis of specific operating conditions when assessing the cost of the structure, taking into account the duration and reliability of operation.
Circuit breakers simpler design, disable the circuit once, cheaper. They can relieve tension manually, but this is usually not very convenient. In addition, at slightly higher currents, they disconnect the load for a long time. This factor may cause an increased fire hazard.
Any fuse protects only one phase of the network.
Circuit breakers more complex, more expensive, more functional. But they are more accurately adjusted to the settings of the protected electrical circuit, selected according to the operating design current, taking into account the switched powers.
The casings of modern machines made of thermosets have increased resistance to thermal effects. They do not melt and are resistant to fire. For comparison, the polystyrene housing of old switches could withstand temperatures no higher than 70 degrees.
The design allows you to select models for simultaneous opening of one to four electrical circuits. If fuses are used in a three-phase circuit, they will remove voltage from the circuit with different time delays, which can become an additional reason for the development of an accident.
Fuses operate on current, without taking into account its characteristics. Circuit breakers are selected for the load and classified by letters:
- An open fuse-link in which there are no devices to limit the volume of the arc, the emission of molten metal particles and flame.
- A semi-closed cartridge with a shell open on one or both sides. It creates a certain danger for people nearby.
- Closed cartridge. It is the most reliable because it does not have all of the above disadvantages. Almost all modern fuses are produced with a closed cartridge.
- G - protects any equipment.
- F - only low current circuits are protected.
- Tr - transformer protection.
- M - electric motors and disconnecting devices.
- Short circuit:
- The fuse link burns out in the shortest possible time;
- Overload:
- The fuse-link burns out within a certain time, which depends on the current value in this mode. The higher the overload current, the faster the fuse burns.
- Normal mode. Heating of the device is a steady-state process in which:
- Full heating occurs to a specific temperature and the amount of heat released is released;
- Each fuse is labeled with its current rating;
- It is necessary to select a consumable element with a certain rated current.
- Fusible element - made of an alloy of various metals or made with specially selected metal alloys.
- zinc;
- lead;
- copper;
- tin;
- silver.
- Housing - a block containing a set of fastening elements that allow the connection of the switching element to the electrical circuit.
- porcelain;
- corundum-mullite ceramics;
- steatite.
- Rated voltage;
- rated current;
- maximum power;
- response speed.
- Electrical fuses are fork. This type of conductive devices often operates in a direct current circuit. The design is made in the form of an arrangement of electrical contacts on one side, and a fusible part on the reverse.
- regular fork;
- forks of miniature sizes.
- Electrical fuses are cork. One of the most common species. The design is based on a body made of porcelain. In the inner part of the case there is a thin wire, which burns out in case of emergency mode. The housing block includes a weight that determines the state of the safety component. Each weight has a specific color, corresponding to the required current strength. If it hangs down on a section of wire, it needs to be replaced.
- DIAZED – applicable in a system whose elements are designed to meet the most varied requirements of installation methods.
- NEOZED - this type allows you to safely replace fusible elements when de-energized.
- Blade-type electrical fuses. This type is used on electrical installation lines, with an operating current value of about 1200 - 1300 A. In turn, they are very dangerous to human health. The use of such types of components in a conductive system leads to very strict compliance with all safety requirements. Only suitably qualified personnel work at such facilities.
- 000 (˂ 100 A);
- 00 (˂ 160 A);
- 0 (˂ 250 A);
- 1 (˂ 355 A);
- 2 (˂ 500 A);
- 3 (˂ 800 A);
- 4a (˂ 1250 A).
- Low current inserts. Their main purpose is to protect low-power electrical circuits. The design has a glass body made in the form of a cylinder with metal elements connected by conductive wire. When a short circuit occurs, the wire burns out, which in turn opens the circuit and keeps the remaining elements of the circuit intact.
- 3 x 15;
- 5 x 20;
- 7 x 15;
- 10 x 38.
- low cost;
- In the event of a high current surge, the electrical fuse completely opens the electrical circuit.
- In the event of a fuse failure, it is possible to simply replace the current-carrying element.
- use the fuse only once, then replace it;
- replacing the current-carrying element with an electrical fuse of a higher rating;
- When using three-phase electric motors, it is recommended to use a phase relay to avoid burning out one of the fuses.
A - electrical networks of increased length;
B - lighting of corridors and areas;
C - power and lighting systems with moderate starting currents;
D—predominant loads from turning on electric motors with high starting parameters;
K - induction furnaces and electric dryers;
Modern electrical networks and devices are very complex and require reliable protection against possible overloads and short circuits. The main protective role in such cases is played by various safety devices. Among the variety of these devices, the most common are fuses, which have a high degree of reliability, ease of operation and relatively low cost.
Despite the widespread use of automatic protective devices, fuse links remain relevant in protecting electronic equipment, automotive electrical networks, industrial electrical installations and power supply systems. They are still used in the distribution boards of many residential buildings due to their reliable operation, small size, stable performance and quick replacement.
What are fuses used for?
If two wires connected to a current source are connected, the well-known short circuit effect will occur. The reason may be damaged insulation, incorrect connection of consumers, etc. With a relatively low resistance of the wires, at this moment a very high current will flow through them. As a result of overheating of the wires, the insulation catches fire, which can lead to a fire.
It is quite possible to avoid negative consequences by including fuses, also known as plugs. If the current exceeds the permissible value, the wire inside the fuse becomes very hot and quickly melts, breaking the electrical circuit at this point.
The design of fuses can be tubular or plug. Tubular elements are manufactured in a closed fiber casing with gas generation properties. If the temperature rises, high pressure is created inside the tube, causing the circuit to break. Plug fuses have a standard design, equipped with a wire that melts under the influence of high electric current.
There is another type of so-called self-healing fuses, made of polymer materials that change their structure at different temperatures. Significant heating leads to a sharp change in resistance towards an increase, as a result of which the circuit breaks. Further cooling causes a decrease in resistance, so the circuit closes again. These fuses are mainly used in complex digital devices. They are not used in conventional power networks due to their high cost.
Sometimes some craftsmen try to replace a blown fuse, using instead so-called bugs, which are a piece of thick wire or thin wires twisted into a common bundle. It is strictly forbidden to use such homemade devices, since the current during a short circuit will be unacceptably high. Extreme heating of the wiring will cause damage, ignition and fire.
Fuse device
The composition includes a housing or cartridge with electrical insulating properties, and the fuse link itself. Its ends are connected to terminals that connect the fuse in series with the electrical circuit, together with the protected device or electrical line. The material of the fuse link is selected so that it can melt before the temperature indicator of the wires reaches a dangerous level, or the consumer fails as a result of overload.
Based on their design features, fuses can be cartridge, plate, plug and tube. The calculated current strength that the fuse link can withstand is indicated on the device body.
Low-voltage fuses have a fairly simple design. Under the influence of high current, the fuse-link or conductive element is subjected to intense heating, after which, upon reaching a certain temperature, it melts in the arc-extinguishing medium and evaporates, breaking the protected circuit. This is how a fuse works in an electrical circuit.
To prevent hot gases and liquid metal from entering the environment, a ceramic insulator is used, also known as the device body, which is resistant to high temperatures and significant internal pressure. The protective covers located at the edges of the fuse are equipped with special strips for unified handles that grip fuse-links when replacing unusable elements. With the help of protective covers and a ceramic housing, an explosion-proof shell is created that limits the switching electric arc.
Sand filling the internal space limits the current. The material is selected with certain crystal sizes, after which it is compacted properly. As a rule, fuses are filled with quartz crystalline sand, which has high chemical and mineralogical purity. The connection of the fuse-link with the base-holder is carried out mechanically, using contact knives. They are made from copper or copper alloys coated with tin or silver.
Fuse characteristics
The main characteristic is the direct dependence of the melting time on the current strength. Therefore, the time during which the fuse link blows out corresponds to a certain current. This parameter is better known as the time-current characteristic.
In addition to the time indicator, there are other characteristics that are used to determine the types of fuses. Among them, first of all, it should be noted. This is the most permissible load current under the conditions of heating the fuse body for a long time. When choosing a device based on this indicator, the load of the electrical circuit must be taken into account, as well as the operating conditions of the fuse.
In some cases, the current rating may be higher than the current in the electrical circuit itself. For example, in electric motor starters to avoid the fuse blowing during starting. It should be taken into account that the rated current of the fuse must correspond to the rated current of the element being replaced.
In turn, the rated current of the element being replaced represents the maximum permissible load current for a long time when this element is installed in the holder or contacts. In addition, there are base and fuse holder current ratings that must be taken into account when selecting a protective device. In addition, an indicator such as rated voltage is used. This parameter represents the interpole voltage, which coincides with the rated phase-to-phase voltage of the protected electrical networks.
In order for fuses to provide reliable protection, the value of this value must be greater than or equal to the voltage of the protected object. For example, a fuse rated 400 volts can be used to protect 220 volt circuits, but not vice versa. Thus, this value characterizes the ability of the fuse to promptly break the electrical circuit and extinguish the arc.
Therefore, when choosing a fuse as a protective device, it is imperative to take into account the parameters that make it possible to ensure reliable protection of the object.
Types of fuses
For all devices of this type, there is a general classification according to their basic properties.
Fuse links can close in different ways, and therefore the external effects that occur when the current is turned off are also different. Such fuses are divided into the following types:
Extinguishing the arc can be done in different ways. Depending on this, fuses are available with or without filler. In the first case, powdery, fibrous or granular components are used, and in the second, due to the movement of gases or high pressure in the cartridge. The designs of the cartridges themselves are divided into collapsible and non-collapsible. The first option involves replacing the melted insert, and in the second case the entire element will have to be replaced. In some cases, non-separable cartridges can be reloaded in special workshops.
Fuses may or may not be replaced while energized. In the first case, replacement can be done directly by hand, without touching live parts. In the second case, the device must be disconnected from the voltage.
Fuse markings
Each fuse in the diagram is indicated by a specific symbol. The standard marking consists of two letter characters. The first letters determine the protective interval: a - partial (protection against short circuits only) and g - complete (protection against short circuits and overloads is provided).
The second letter indicates the types of protected devices:
More detailed information about fuse markings can be obtained from reference books intended for electrical engineers.
One of the important components of the conductive system that performs a protective function is the fuse. These devices come in various configurations and have many models. This article will talk about the fuse. Each block has its own current-carrying elements, so the conductive element takes an important part in the stable operation of electrical circuits. It should be noted that the concepts of fuse and fuse link have slightly different definitions. This article will help you understand this difference.
Operating principle
The basic feature of the fuse is that its combustion in the electrical circuit occurs much earlier than other elements. In the event of a current surge in an electrical circuit, it is much easier and faster to replace a fuse than to change live wires, microcircuits, etc.
This element received the name fusible because the main element of its design is a fusible insert. This component has a low melting point; according to the Joule-Lenz law, when current passes through a conductor, thermal energy is released in it, and the fuse burns out at a high current value, which is dangerous for other components. This leads to an open circuit. Thus, the fuse protects the remaining elements of the electrical circuit from damage.
Fuse operation modes:
When choosing the required fuse, you need to be guided not only by the current value indicated on the housing. But also the permissible operating voltage and time-current characteristics.
The time-current characteristic is necessary to indicate the magnitude of the change in the time of complete circuit break when a current of a certain value is supplied.
Design
The main element included in the fuse is the fuse link. These inserts have many configurations, but nevertheless have two basic elements:
Fuse links are made of various materials:
The cases are made from varieties of durable ceramics such as:
When using electrical fuses with low rated current, the housing is made of special glass.
The main parameters characterizing fuses include:
All these factors must be taken into account when calculating the fuse link.
Calculation of fusible rated current values is carried out according to formula 1:
From the formula, for calculation, you need to know U - voltage, Pmax - maximum load power.
Types of fuses
The main and most important step is the selection of fuse links. This is necessary, taking into account the various conditions in which the following types of electrical fuses are used:
Fork safety elements are divided into:
Types of configurations and purpose:
The rated current of the fuse link is selected based on the maximum power of the network.
Current values according to the color of the check
Blade electric fuse is divided according to current value:
Such enclosures are made with different overall dimensions (in mm):
To summarize the consideration of fuses, it is worth noting that fuses must be used in many electrical devices in order to avoid damage to their elements. In addition to the above, it makes sense to pay attention to their advantages and disadvantages.
Advantages:
Flaws:
Recently, many manufacturers have been using modern quality standards for development, so that the block of each conductive element can adequately compete with European and world analogues.
Thus, protecting electrical circuits using various fuses is one of the simplest, most reliable and cheapest ways.
Video about fuses
