Fuse selection of wire for repair. Calculation of fuses Wire cross-section for fuses table
In modern electrical appliances, fuses are found everywhere, or, to put it scientifically, fuses. They protect the network and the device itself from short circuits or overload. The design of fuse links is very diverse, as are the sizes. The rated currents and voltages for which fuses are issued correspond to standard values. Its overall dimensions, namely length, depend on the rated voltage of the fuse; the higher the rated voltage of the fuse, the greater the distance between the contacts. The rated current is determined by the cross-section of the wire inside the fuse.
Although self-resetting electrical fuses can now be found in more expensive devices, most devices are still equipped with conventional fuses.
General concepts, introduction to tubular fuses
The most common fuses are the so-called tubular ones. They are a ceramic or glass tube with metal cup contacts at the ends. These cups are connected to each other by wire, the cross-section of which, as already mentioned, determines the rated current of the fuse. This current is indicated on the tube or one of the contact parts of the fuse. For example: F0.5A - this means that this fuse is rated for a current of 0.5 amperes.
On electrical circuit diagrams, a fuse is indicated by a rectangle with a straight line passing through it. Next to the conventional graphic designation its position designation is indicated, for example F1 (F – fuse, fuse in English); and if this does not clutter the circuit - the rated current, for example 100 mA.
Description of the operating principle of a fuse link (fuse)
The principle of operation of the fuse is extremely simple. When a rated current flows through the wire connecting the fuse contacts, this wire heats up to a temperature of about 70 °C. But when the current is exceeded, the wire heats up more, and when the melting temperature is exceeded, it melts, i.e. burns out. It is for this reason that fuses are also called fuses or fusible links. The higher the current, the faster the heating, the faster the melting occurs, and, accordingly, the fuse blows.
Thus, all fuse links operate on the same principle - excess current in the circuit causes overheating and melting of the wire inside the fuse and, as a result, disconnection of this circuit from the power source.
There are two main reasons for the burnout of fuse links: surges in the supply voltage and a malfunction within the electrical appliance itself.
Checking the fuse, fuse fault indicator
You can check the fuse-link with any continuity tester or tester. The goal is to ensure that the fuse circuit is intact and capable of conducting electrical current.
To avoid electric shock, checking the fuse is only allowed when the electrical appliance is turned off!
In addition, you can buy or make your own fuse blown indicator, which will notify you that the fuse has blown.
The circuit diagram of such a device is extremely simple and is shown in the following figure.
LED HL1 is connected in parallel to the fuse contacts, through current-limiting resistor R1 and diode VD1, to protect against reverse voltage. Diode VD1 must be selected based on the reverse voltage exceeding the mains voltage. For a 220 V network, the reverse voltage for the VD1 diode must be at least 300 V; for example, the 1N4004 diode or the domestic KD109B meets these requirements.
The indicator does not light if the fuse is good, and lights up if it is blown.
This circuit is very convenient to complement home-made power supplies.
By slightly changing (simplifying) the circuit, you can get a fuse blown indicator on a neon lamp, although it does not look as effective as an LED.
Selection of fuse according to the rated power of the electrical appliance
After checking the fuse and determining that it has failed, it must be replaced. And to do this, you need to find out its denomination in order to make the correct replacement.
If you know the power consumed by an electrical appliance, it is usually indicated on the nameplate of the device, you can independently calculate the rated current of the fuse using the following formula:
Inom = Pmax / Unom
The rated current (Ampere) is equal to the quotient of the maximum power (Watt) of the electrical appliance divided by the rated network voltage (Volt).
For example, a fuse in a TV has blown, it is not possible to make out what is indicated on the fuse body, its rating, but the power consumption of 150 VA is indicated on the TV nameplate.
150 / 220 = 0.68, rounded to the nearest higher standard value - 1 A.
Please note that when calculating the fuse current rating you are getting an exact current value which may not correspond to a range of fuse ratings. Therefore, the calculated value taking into account the 5% margin is rounded to the nearest standard value.
For simplicity, you can use a ready-made table that shows the ratings of standard fuses for various consumers based on their connection to a 220 V household network.
Replacing the fuse
When replacing a fuse, to avoid electric shock, be sure to unplug the electrical appliance!
There is an unspoken rule: if after the second replacement the fuse blows again, look for a fault in the electrical appliance itself. This means that the electrical appliance needs to be repaired.
Do not install a fuse at a higher current under any circumstances; such attempts will definitely lead to even greater damage to the device, up to the point of its being beyond repair!
Be careful when purchasing a new fuse. Correctly determine the type and current rating of the replacement candidate. It is better to purchase electronic components from trusted suppliers who guarantee product quality, such as Conrad Electronic. The full range of fuses can be found at the link - https://conrad.ru/catalog/predohraniteli_s_plavkoy_vstavkoy.
Fuse repair
Typical people believe that fuses cannot be repaired; in fact, this is not the case. Most types of fuses can be repaired and given a second, third, etc. life. The fuse housing, as a rule, is destroyed extremely rarely, the wire inside burns out, and the repair consists of replacing it. The main task is to use a wire similar to the one in the fuse.
If you need to replace a fuse very quickly, but you don’t have a spare at hand, you can use the following method:
Remove the paint coating from the wire (clean it until it shines) and wind several turns around each fuse contact, then insert the fuse into the holder. This method is popularly called “bug”. With its help you can very quickly check the serviceability of the device, but it is not reliable and can be used as a temporary solution to the problem.
The next method is the so-called “factory” one. Repairs will require a soldering iron, and perhaps a Dremel or screwdriver, but the fuse after repair will look like it came straight from the factory.
Heat the ends of the cup contacts with a soldering iron and remove the solder from the holes in the ends using a toothpick or something similar. It happens that the holes are too small or completely absent, then you will have to drill them. Use a drill of small diameter 1 - 2 mm.
Pass a wire of a suitable diameter through the holes and solder it to the cup contacts.
The fuse is ready!
Selecting the diameter of the fuse wire
As written above, to repair a fuse, it is necessary to replace the burnt wire with one similar to the one that was in the fuse before it burned out.
Factory fuses use wires made of various metals: silver, copper, aluminum, tin, lead, nickel, etc. At home, it is unlikely that we will be able to determine the material of the wire of a blown fuse, and we also have ordinary copper wire at hand. But just in case, we present a table of wire diameters depending on the rated current of the fuse, containing, in addition to copper, aluminum, steel and tin.
| Fuse current, A | 0,25 | 0,5 | 1,0 | 2,0 | 3,0 | 5,0 | 7,0 | 10,0 | |
| Wire diameter, mm | Copper | 0,02 | 0,03 | 0,05 | 0,09 | 0,11 | 0,16 | 0,20 | 0,25 |
| Aluminum | - | - | 0,07 | 0,10 | 0,14 | 0,19 | 0,25 | 0,30 | |
| Iron | - | - | 0,13 | 0,20 | 0,25 | 0,35 | 0,45 | 0,55 | |
| Tin | - | - | 0,18 | 0,28 | 0,38 | 0,53 | 0,66 | 0,85 | |
| Fuse current, A | 15,0 | 20,0 | 25,0 | 30,0 | 35,0 | 40,0 | 45,0 | 50,0 | |
| Wire diameter, mm | Copper | 0,33 | 0,40 | 0,46 | 0,52 | 0,58 | 0,63 | 0,68 | 0,73 |
| Aluminum | 0,40 | 0,48 | 0,56 | 0,64 | 0,70 | 0,77 | 0,83 | 0,89 | |
| Iron | 0,72 | 0,87 | 1,00 | 1,15 | 1,26 | 1,38 | 1,50 | 1,60 | |
| Tin | 1,02 | 1,33 | 1,56 | 1,77 | 1,95 | 2,14 | 2,30 | 2,45 | |
Calculation of fuse wire diameter
If you need a fuse for a current not listed in the table above, you can use the formula to calculate the diameter of the copper wire depending on the rated current of the fuse.
For low currents (using thin wire with a diameter of 0.02 to 0.2 mm), the formula is as follows:
d = Ipl k + 0.005
For high currents (when using wire with a diameter of more than 0.2 mm), the formula is as follows:
Where Ipl– fuse-link current in amperes, To And m coefficients depending on the conductor material can be determined from the following table.
Determining the diameter of the fuse wire
On factory coils, the wire diameter is indicated along with other parameters. What to do if the wire is taken from a piece of stranded wire? The diameter of the wire can be measured with a micrometer. But even if you don’t have a micrometer, you can use the old fashioned way - measure the diameter of the wire using a ruler or caliper. It may not be as precise, but for our case it is quite acceptable.
We take a ruler and wind 10 to 20 turns on it. The recommended winding width is about a centimeter. At the same time, we try to ensure that the coils fit as tightly as possible. We count how many millimeters our turns took and divide this number by the number of turns. It is not necessary to wind it on a ruler, if the piece of wire is short, you can use a pencil, screwdriver, lighter or any other object for winding. The main thing is that the turns are wound evenly and tightly.
For example, the width of the wound turns is 9 mm, with a number of turns of 20. Dividing 9 by 20, we find that the diameter of the wire, if we discard another 0.05 mm for the gaps between the turns, is approximately 0.40 mm. Using this wire it will be possible to restore a 20 A fuse. That's so simple and quite accurate!
And finally, a video demonstrating the burnout of the fuse link:
Primary interest in the topic arose due to the lack of commercially available 200 mA fuses, the same ones used by the manufacturer in the Mastesn multimeter. I tried setting it to 160 mA, but nothing good came of this idea - they “burn” almost after every measurement. I set it to 250 mA (no incidents so far). And since I go towards achieving a goal with a bit of passion, and besides, I’m no stranger to finding a way out of difficult situations “at random,” it’s not so rare to have to change burnt fuses. My next voyage to places selling electronic components, this time regarding 0.5 and 1 ampere fuses, was again disappointing. Fortunately, radio amateurs don’t have the habit of throwing anything away (they can only pick it up and get it in any available way), so a certain number of blown fuses have already accumulated.
Repairing a fuse, or as they used to say in the old days, “putting a bug,” as I initially imagined, is not at all a tricky matter. There are plenty of instructions on this matter on the Internet. All it takes is finding wires of suitable thickness, and the rest is a matter of technique.
True, there was no information on where to find the necessary wires with a diameter of 3 microns (0.03 mm).
However, we were lucky, and a wire with a diameter of 0.03 mm was found in the coil of the frame of the measuring head that could not be restored. From where it was taken using a powerful watch magnifying glass, acetone and a certain amount of patience.
A wire with a diameter of 0.05 mm was found on the board of the Slava electronic-mechanical alarm clock. There were no more problems here, you just had to dip it in acetone, and the wire from the reel began to unwind on its own. After communicating with a wire with a diameter of 0.03 mm, this one was already like a “rope”.
The next step was opening the fuses. This became possible only after heating the metal caps with a soldering iron. Now, wise from practical experience, I know that you only need to shoot one of them. The next step in the end part of the caps, using a well-heated soldering iron with a thin tip, was to remove the tin from the holes through which the wire that functions as a fuse is passed directly.
First repair operation. A wire of the required diameter equal to twice the length of the fuse being repaired is passed through the hole in the first cap, the glass body and sealed. With the obligatory preliminary removal of varnish insulation from the edge (if it remains after acetone).
The second step is to place the cap on the glass body using glue (the most convenient brand is BF-6).
The final operation is to pass the wire into the hole of the second cap and also solder with subsequent gluing. Immediately after soldering, you need to check the fuse with a multimeter.
After trimming the ends of the fuse wires protruding from the outside, you can lay out the ready-to-use products in even rows, but so that they do not get mixed up in any case, and admire the creation of your hands. I was especially pleased that we were able to repair miniature specimens. Sometimes these are really needed.
And the last step - the previous markings were removed from the metal caps, now serviceable fuses, using a file (now I know that it is much more convenient to do this at the very beginning of the repair). Everything is packaged in bags and ready to use.
Epilogue: in case of emergency, repairing fuses is possible, even with a nominal value of 0.5 A. A micrometer is required.
Using a similar strategy, you can repair car fuses (fuse links) and many others. I imitated the Tula “Lefty” Babay.
Discuss the article REPAIR OF FUSES
No electrical network can guarantee constant voltage to its consumers. Moreover, a power surge can happen at any moment, and it is simply impossible to predict it in advance by turning off all equipment from the network. That is why one of the important elements of electrical wiring and household appliances is a copper wire fuse or fuse link that protects equipment from short circuits.
Almost all residents of our country have previously encountered the principle of operation of such fuses, since they served as a protective element for household electrical wiring in apartments and houses. They were equipped with the same plugs that, when the load on the network was too heavy, cut off the power supply. In most cases, this happened precisely because the copper wire in the fuse burned out. Today such equipment is extremely rare - except in old village houses. Instead, more modern devices are used - reusable circuit breakers. They are triggered by an unacceptable excess of voltage in the network. Once the danger of a short circuit has disappeared, the switch can be turned on again.
As for household appliances, most of them today still have fuses made of copper wire, and it must be said that a more reliable way to protect the device from excessive voltage does not yet exist. In addition, fuse links are used in cars and are by far the most reliable (and, by the way, cheapest) means of protecting the electrical part of a car from failure due to a short circuit.
What do copper wire fuses look like and do?
In appearance, a fuse is a glass or ceramic flask with a calibrated copper wire stretched inside it. It is attached to the element contacts located in the metal caps using soldering or spot welding. The diameter of the wire depends on the current for which the fuse is designed. The flask (tube) of a product with a high rated current is sometimes filled with quartz sand. Because of their appearance, such fuses are called tubular.
Another common type of this device is knife-type automotive fuse links. Depending on the current rating, they are painted in different colors:
- 5 A - orange;
- 7.5 A - brown;
- 10 A - red;
- 15 A - blue;
- 20 A - yellow;
- 25 A - colorless (transparent);
- 30 A - green;
- 40 A - purple;
- 60 A - blue;
- 70 A - black.
The operating principle of the insert is extremely simple. The fuse is turned on and electric current begins to flow through the wire. The wire heats up. As long as the current does not exceed the fuse rating, the wire temperature remains at approximately 70 degrees Celsius. As soon as the current values exceed the permissible limits, the heating of the wire increases to the melting temperature of copper, it loses its integrity, thus breaking the electrical circuit. All this happens very quickly, almost in a split second. It is because of this principle of operation that fuses with copper wire are called fuse links.
There are different types and types of such inserts. But regardless of this, they all act the same way: the copper wire they contain melts and the current flow is interrupted.
It is very important to understand that the fuse “trips” precisely when the permissible current value is exceeded, but the voltage in the network has no meaning for it. In other words, the same element can be installed in both a 12-volt charger and a single-phase or three-phase network.
Naturally, the question may arise: we say that the device protects against power surges in the network, and then we claim that voltage is not important for it, how is this possible? In fact, here it is enough to recall the school physics course, namely Ohm’s law, which states that the current strength in a section of a circuit is directly proportional to the voltage and inversely proportional to the resistance. In other words, the higher the voltage, the higher the current, given that the resistance of the conductor (copper wire of a certain diameter) in any case remains unchanged.
An insert can burn out not only due to voltage surges in the network, that is, due to exceeding the rated current, but also due to a malfunction inside the device itself in which it is installed. You can determine the reason for the failure of the insert yourself - if after replacing it twice, the element burns out again, it means that the device itself is faulty. Sometimes a situation occurs when the reason for the failure of an insert is its poor quality, but this is rare.
What to do if the fuse breaks?
There is an opinion that a fusible link is an element that cannot be repaired. And the only way out if it burns out is replacement. Moreover, it is very important to choose the right new fuse while maintaining its rating, that is, the maximum permissible current - otherwise it will not be the fuse that will burn out, but the entire device. If it is not possible to determine the rating from a burnt product, then you must select it based on the power of the device, which is usually indicated on its body or on the label. In order to calculate the current, you can use the formula:
Inom = P max / U, Where
I nom- fuse rating, measured in amperes (A);
Pmax- maximum power of the device, measured in watts (W);
U- voltage in the electrical network where the power comes from, in volts (V).
Another way to determine the required insert rating is to look at it in a special table, which indicates which standard fuse is used for a particular maximum power of the device:
- 10 W - 0.1 A
- 50 W - 0.25 A
- 100 W - 0.5 A
- 150 W - 1 A
- 250 W - 2 A
- 500 W - 3 A
- 800 W - 4 A
- 1000 W - 5 A
- 1200 W - 6 A
- 1600 W - 8 A
- 2000 W - 10 A
- 2500 W - 12 A
- 3000 W - 15 A
- 4000 W - 20 A
- 6000 W - 30 A
- 8000 W - 40 A
- 10000 W - 50 A
But in many situations it is not possible to replace the fuse with a new one. For example, when a fuse element in a car electrical system has burned out, and you are far from stores where you can buy a replacement. In this case, it is worth knowing that almost any failed fuse can be “reanimated”. Indeed, in most cases, the only thing that distinguishes a working element from a non-working element is a burnt copper wire. And it can always be replaced, without changing the technical characteristics of the product itself. The main condition is to maintain the wire diameter, then the device will work as before.
How to repair a fuse.
In the industrial production of fuses, wires made of various materials are used (copper, aluminum, tin, lead, nickel, silver, etc.) - it all depends on the magnitude of the current and the requirements for the device’s response speed when the rating is exceeded.
When repairing an insert, only one option is possible - using red copper wire. Finding such a wire is not at all difficult - for sure, any master has small pieces of wire left over after laying or repairing electrical wiring.
The main task is to correctly determine the diameter of the wire based on the fuse rating. If this parameter cannot be determined from the element itself (for example, the number has become unreadable), the power of the device is taken as a basis. In this case, one important rule must be observed - the maximum permissible current of the insert must be greater than the current required by the device when operating in maximum mode. For example, if the product is designed for a maximum current of 1 ampere, then a protective element of 2 amperes is selected. Once you have decided on the fuse rating, you should select the wire diameter using the following data:
- for a fuse with a current of 0.25 A, a wire with a diameter of 0.02 mm is required;
- fuse 0.5 A - wire diameter 0.03 mm;
- 1 A - 0.05 mm;
- 2 A - 0.09 mm;
- 3 A - 0.11 mm;
- 5 A - 0.16 mm;
- 7 A - 0.20 mm;
- 10 A - 0.25 mm;
- 15 A - 0.33 mm;
- 20 A - 0.40 mm;
- 25 A - 0.46 mm;
- 30 A - 0.52 mm;
- 35 A - 0.58 mm;
- 40 A - 0.63 mm;
- 45 A - 0.68 mm;
- 50 A - 0.73 mm;
- 60 A - 0.83 mm;
- 70 A - 0.91 mm.
The next step is to determine the diameter of the wire you have. There is a special tool for this - a micrometer. But it is difficult to call it very widespread. As a rule, only craftsmen who do this kind of work professionally have it. You can also determine the diameter of the wire using a regular ruler. To do this, you need to tightly wrap several turns of wire around the ruler (it should occupy at least 1 cm), and then divide the number of closed millimeters by the number of turns. The result will be the diameter of the wire. If the length of the existing segment does not allow you to wind it directly onto the ruler, use any other object - for example, a pencil or a match.
After this, you can proceed directly to repairing the fuse. The easiest way is to strip the wire and wind it around the metal caps of the tubular insert. It is necessary to make several turns to ensure that the wire holds firmly. True, this method can hardly be called very reliable, and most often it is used when they want to check whether the device itself is working. If, after installing such an element in the circuit, the wire burns out, then the device requires repair.
A more complex, but also more reliable way to repair the insert is as follows:
- we warm up the metal caps using a gas burner or a regular lighter and remove them from the glass flask, holding it carefully through the cloth;
- if there is glue left inside the caps, it must be removed - this will help make the contact more dense;
- We strip the wire and pass it diagonally through the flask;
- put on the caps.
In order to more securely fix the wire in the caps, it can be soldered by passing it through the holes in the ends of the caps. In this case, the repaired fuse will be absolutely no different from the factory one.
A homemade copper wire fuse can be a great temporary way to replace a blown fuse. But if you decide to do this, then it is extremely important to choose the right cross-section of the very conductor that you will use. Why is this important, what are the reasons for blown fuses and ways to temporarily eliminate this inconvenience we will consider in our article.
Let's start with the most important thing - the reasons for blown fuses. After all, nothing just happens, and before installing a bug, you need to determine the reasons for the fuse failure.
There may be several of them:
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The most common and common cause of a blown fuse is a short circuit. As a result of this event, the current increases sharply, to which the fuse link in the fuse reacts, burning out. |
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It is also quite common for a conductor to burn out when the drive mechanism of the supply circuit becomes jammed. In this case, the fuse acts as overload protection. |
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The next possible reason that you need to look for a wire for a fuse could be a voltage surge. With a sharp and, most importantly, long-term decrease in voltage, the current, according to Ohm's law, increases proportionally. This may cause the fuse to blow. With short-term jumps, this happens extremely rarely. |
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Another possible option is the frequent operation of the fuse on the verge of tripping. When the current flowing through it is close to the rated current, the fuse wire becomes very hot. Then it cools down and heats up again. This mode changes the structure of the metal, which is why the fuse can blow at significantly lower current values. |
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It is to eliminate such cases that high-quality fuses are made from the purest possible metals. Their structure changes due to frequent temperature changes are minimized. |
Selecting wire diameter and fuse repair
Well, now let's move on to the main issue of our article - the choice of diameter and the repair itself. Let's start with the first one.
Conductor diameter selection
The diameter of the conductor in the fuses is clearly calculated. If you are replacing, you must install a conductor of the same diameter. Otherwise, your fuse will not perform its function of protecting the electrical network.
- There are several ways to do this. The easiest way is to take the wire cross-section for the fuse, and a table of standard values will allow you to make a choice. To do this, just measure the diameter of the wire.
- The diameter of the wire can be measured using a caliper or even a regular ruler. If the diameter of the fuse wire is too small, then measurements can be made as follows. We wrap the wire around any small object - a lighter, a pencil, a pen.
- It is advisable to make 10-20 turns for greater measurement accuracy. We make the coils as dense as possible to eliminate the space between them. Then we measure the diameter of all turns. We divide the resulting value by the number of turns. Here is the diameter of the wire for the fuse.
Ten of them were killed immediately.
220 volts is no joke.
How to repair a fuse, how to select a wire or wire to replace the fuse thread.
Hello!
Repairing a fuse has to be done when it has burned out and the store is closed or located far away, but using an electrical appliance without a fuse, and everyone should know this, is far from safe. I partially touched on the issue of fuses in this article, where the principle and purpose of fuses were discussed.
In the best case, a device with an installed “bug” will burn out in such a way that it becomes clear why the fuse failed; in the worst case, this can lead to a fire and other equally harmless consequences.
We will mainly touch on low-power fuses. But their principle is the same. A ceramic or glass tube (maybe another modern material), inside of which there is a wire or plate, and in powerful fuses of the PN-2 type, the space around the wire can be filled with quartz sand or other arc-extinguishing material. Low-power fuses usually do not have any filling material.
So, your fuse has blown (otherwise you probably wouldn’t be looking for this material) and you need to “reinvent the wheel.” Look at the photo and you will see that the fuse consists of a glass tube and two metal caps. The pitfall here creeps up unnoticed - it is not always possible to remove the cap without damaging the tube, since not only does it fit tightly, but it also happens to be glued.
How to disassemble a fuse.
Based on the above, there are four options:
Why is it bad when the wire is outside. The higher the voltage used, the more it tends to “escape”. Such a track for high voltage can even be soot, let alone a thin layer of copper, which can spread under the influence of high current. This is why it is important to enclose the conductor in a tube and other protective material. And it is for this reason that it is not recommended to get too carried away with the fuse restoration procedure. Over time, a lot of soot and molten metal accumulates and the voltage forms an arc through which current also flows freely.
All other fuses are structurally similar. If you still have a problem and you cannot approach the fuse, write a question in the comments. I am on the site at least once a day, so you will receive a response promptly.
Fuse calculation online.
All that remains is to determine what to make the wire from and how to calculate it.
Most often, the wire is made from copper wire (it can be tinned, it doesn’t matter much). But to prevent the fuse from becoming a bug, you need to select the correct wire cross-section. To do this, you can use tables:
So also with calculations in the form of an online calculator, which I will post below. First, let's talk about calculations. If you do not yet know about the continuous permissible current, then you need to get acquainted with this concept, and if you do, then you will be surprised by carefully looking at the table. For example, a wire with a cross-section of 2.4 mm² can withstand a current of 300 amperes. It would seem, why then is it protected by a 25 ampere circuit breaker? The fact is that at 300 amps it gets very hot. If there was insulation on it, it would have long ago turned to ash at such a current.
Wire diameter for fuse.
How to determine the diameter of a wire. There are three methods for this:
What do you need to know about this formula?
You may notice that a strange coefficient of 1.885 has been added. The fact is that the cross-section of the wire in some strange way does not correspond to the mathematical formula for calculating the area of a circle, and if you do not apply this coefficient, you will get a completely different result. You can trust me. I didn’t just paste this formula in from somewhere, I did some calculations (and more than one before I wrote it here). For those who are interested in repeating this, you will need a micrometer and a bunch of different wires. Perhaps your coefficient will become more accurate, but within this figure. This coefficient is valid for copper wire, for aluminum it will be 1.309, for other materials it may also be different. ( There are different formulas on the Internet, but as I said, I don’t know where they came from, I did my calculations before giving this formula). Well, what about without the practical part. Let's say we have a 0.5 mm² wire and 15 wires. 0.5/15 = 0.033 mm² cross-section of one wire, now we substitute the result into the formula and get 0.282 mm. We look at the table and find that a wire with a diameter of 0.25 can withstand 10 amperes, which means ours will withstand about 12 amperes.