General calculation rules
In order to make the correct calculation of fuse links, it is necessary to take into account the rated voltage.
This value should be such that the fuse switches off the electrical circuit. The main indicator is the minimum voltage provided for the base and fuse-link. Another important indicator that should be taken into account in the calculations is the shutdown voltage. This parameter is the instantaneous value of the voltage that appears after the fuse or fuse link itself has tripped. As a rule, the maximum value of this voltage is taken into account.
In addition, the melting current must be taken into account, on which the diameter of the wire installed inside depends. When calculating a fuse link, for each metal this indicator has its own value and is selected using a table or calculator. The material and size of the inserts must provide the required protective characteristics. The length of the insert cannot be too long, as this will affect arc extinction and overall temperature characteristics.
The rated load power is usually indicated on the product label. In accordance with this parameter, the rated fuse current is calculated using the formula: Inom = Pmax/U, in which Inom is the rated protection current, Pmax is the maximum load power, and U is the supply voltage.
Wire M2
It is primary copper, which has a high content of the base metal and a minimal amount of impurities. M2 wire is made from copper alloy having a technical purity of no less than 99.7%, and impurities of no more than 0.3%, respectively (the same elements as in the M1 grade). The percentage of oxygen is not more than 0.08.
According to the production method, copper wire M2 is: M2b (oxygen-free), M2f (deoxidized with phosphorus), M2k (cathode), M2r (deoxidized with oxygen). According to physical parameters, they are divided into: hard (M2T) and soft (M2M) rolled copper.
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.
Note! With this method of measuring diameter, you will probably have a small error due to insufficient density of turns. Therefore, we round the resulting number to the nearest smaller number.
- Calculation of a copper wire fuse can also be made for values not indicated in the table. To do this, we need to know the required fuse-link current and wire material.
- In order to calculate the diameter of the copper wire for a fuse up to 7A, we should use the formula below. In this formula, d is the calculated diameter, Ipl is the required fuse-link current, k is a coefficient taking into account the wire material. For copper it is 0.034.
- If you want to calculate the diameter of the wire for an insert with a rating above 7A with your own hands, then you should use the formula given below. In this formula, m is a coefficient that takes into account the wire material. For copper it is 80.
- If the thickness of the wire for the fuse, as a result of calculation or selection from the table, turns out to be one that is not available. Then you can achieve the required diameter by connecting several wires of different sections. Although this option is somewhat worse.
Fuse repair
Installing a wire instead of a calibrated fuse in a fuse is popularly called installing a “bug”. Any “bug,” according to the PUE standards, is unacceptable, since it is not always capable of properly protecting the electrical installation.
Nevertheless, this method of repairing fuses is resorted to quite often. Especially when there is no spare fuse at hand.
- Installing a bug instead of a fuse depends on its type. If this is a tubular fuse with a high rated current, then such products usually have a collapsible design, as in the video.
- That is, the fuse can be untwisted. Remove the burnt-out fuse-link and replace it with a fuse made of copper wire.
- With products of lower denominations everything is a little more complicated. Usually they are made non-separable, and therefore you have to tinker.
- If you have a glass or ceramic type tubular fuse, they usually have metal ends. To install the “bug” they need to be drilled on both sides and our conductor inserted into the resulting cavity. It is advisable to then solder the hole together with the conductor.
- Do-it-yourself repairs with knife fuses are somewhat more difficult. It will not be possible to drill a hole here, since the wire must be attached to the knives, which are hidden under the body. In this case, the wire cross-section of a 10 A fuse or another rating is attached directly to the knives in front of the housing. And then install the fuse.
Note! This method is much more dangerous. Since when a wire burns out, it may splash onto neighboring equipment. This may not lead to a fire, but it can damage the equipment.
- It is for these reasons that our instructions do not recommend winding wire directly onto the fuse holder contacts. The same applies to winding the wire on top of the tubular fuse housing.
Rule for choosing wire cross-sectional area for maximum current
You can select the required cross-sectional area of the copper wire based on the maximum current using this simple rule:
The required wire cross-sectional area is equal to the maximum current divided by 10.
This rule is given without reserve, back to back, so the result must be rounded up to the nearest standard size. For example, the current is 32 Amps. You need a wire with a cross section of 32/10 = 3.2 mm2. We choose the closest one (naturally, in the larger direction) - 4 mm2. As you can see, this rule fits well into the tabular data.
Important note. This rule works well for currents up to 40 Amps . If the currents are greater (this is already outside the boundaries of an ordinary apartment or house, such currents are at the input) - you need to choose a wire with an even larger margin - divide not by 10, but by 8 (up to 80 A)
The same rule can be stated for finding the maximum current through a copper wire with a known area:
The maximum current is equal to the cross-sectional area multiplied by 10.
And in conclusion - again about the good old aluminum wire.
Aluminum conducts current less well than copper. This is enough to know, but here are some numbers. For aluminum (the same cross-section as the copper wire) at currents up to 32 A, the maximum current will be only 20% less than for copper. At currents up to 80 A, aluminum conducts current 30% worse.
For aluminum the rule of thumb would be:
The maximum current of an aluminum wire is equal to the cross-sectional area multiplied by 6.
I believe that the knowledge given in this article is quite enough to choose a wire based on the ratios “price/thickness”, “thickness/operating temperature” and “thickness/maximum current and power”.
That’s basically all I wanted to tell you about the cross-sectional area of the wires . If something is not clear or you have something to add, ask and write in the comments. If you are interested in what I will publish next on the SamElectric blog, subscribe to receive new articles.
How to choose power wiring
The power cable must be compatible with the system it powers. If the cable is not thick enough, there will be large losses in it, that is, “sagging,” as this phenomenon is now commonly called. It is due to the fact that the cable has, although vanishingly small, resistance.
It is really very small, about 0.3 - 0.8 Ohm per km of cable length. But it still exists, and at high currents on the line, losses can be noticeable.
Selection of cable cross-section
In order to select a cable of the required cross-section, you do not need to calculate anything. You can, of course, set the current consumption, the permissible drawdown, for example, the current in the system is 100A and the drawdown is no more than 0.5 V, and calculate the required cable cross-section, taking into account the length of the line. This is not necessary. There is an old rule of thumb for selecting the cross-section of a power cable, which for simplicity is called “five amperes per square”:
It is based on the fact that the length of the line from the source to consumers (to amplifiers) does not exceed 5 m. This is 99% of all cases. What does this rule mean? This is the standard for current density. With a current density of five amperes per square millimeter, losses on a cable up to 5 meters long will be no more than 0.5V. Precisely no more than 0.5, this is important at maximum, and not operating, current.
How to use this rule? Take the amplifier and see what its fuse rating is. If there are several, consider the total denomination. If you have several amplifiers and you will power them with one cable, add up the ratings of their preamps. We take the result obtained as the maximum current consumption. The real worker will be noticeably smaller. We divide the maximum current by 5 and get the required cable cross-section (“5A per 1 sq mm).
Next, take the next larger standard cable cross-section. Example. We have an Oris TA-150.4 amplifier. It has a 100A fuse installed on it. Typically, the manufacturer provides a margin of 10-20% when selecting a fuse. Accepts maximum current for 100A. Divide 100 by 5 to get 20 squares. To power such an amplifier you will need a cable with a cross-section of at least 20 sq mm. We select the following standard cable cross-section - 25 sq mm. All. To power the Oris TA-150 amplifier.
4, a cable with a cross-section of 25 square millimeters is necessary and sufficient. You can use a cable that is one section larger, and it won’t be any worse. Will it be better? Practice shows that if you take a cable two or more sizes larger, it will definitely not be better. Losses on the cable are already approaching zero.
Use the “five amperes per square” rule, select the required cable cross-section or one size larger. Buying a thicker cable will not be advisable.
The drawdown lives not only on the cable. And, for example, also on the fuse.
Fuse selection
A fuse on the power line must be required and must be installed not far from the power source. In an emergency, it must protect the power source from short circuit. It doesn’t matter what happened, the cable frayed and shorted to ground, or the amplifier burned out and somehow shorted it. The fuse must blow to prevent the wiring from catching fire.
The operating principle of a fuse is simple and is based on Ohm's law for a complete circuit.
Where Un is the voltage drop across the system elements: at the wiring, at the limiter, at the amplifier itself, etc.
These are all dips of their kind, but we don’t call the voltage drop across the amplifier that way. The magnitude of the voltage drop depends directly on the resistance of the system element and is always many times less than the voltage drop on the main link - the amplifier. So far so good, the losses on the cable and fuse are not significant, everything works. Now let’s imagine that some emergency has occurred. The wiring has shorted.
Of all the elements of the system connected to the power source (battery), only the power cable and fuse remain (the amplifier has fallen out of the system). And all its energy will be dissipated precisely on the cable and at the limit. Which one will burn out first, the wire or the front? For a fuse to blow, the drawdown on it must be much greater. Then it will work stably. Therefore, the fuse must be selected strictly according to the cable.
Not by current consumption, but specifically by cable cross-section.
The fuse rating is also selected according to the “five amperes per square” rule. Only in the opposite direction. Let's say you need to select a fuse for a cable with a cross-section of 25 squares, which powers the same Oris TA-150.4 amplifier. Multiply 25 by 5, we get the required rating of 125A. The next larger one is rated 150A.
If the power wiring is selected according to the described rule, the system operates stably, with a good margin, and in the event of a short circuit, the fuse operates clearly. Cable and fuse losses are very small. There is no need to remove the fuse. This is sometimes done in competitions to reduce drawdown. But we don’t need this at all for everyday use.
Useful tips
When working with wires, it is advisable to adhere to some recommendations:
- When working with mixed wires, it is necessary to use terminal blocks. This way you can avoid oxidation in the connections of two different metals, otherwise overheating may occur, which will lead to a short circuit or, even worse, to a fire;
- It is necessary to select the correct cross-section of the conductors, taking into account the power of electrical appliances, otherwise the wiring may burn out when turning on powerful devices;
- When laying cables underground, it is worth using products with armored insulation. It will protect the wires from heavy loads;
- The cable can only be laid at temperatures above 15°C; in colder conditions, the wire must be heated with a heat gun;
- Do not use a cable with damaged insulation. Even if the damage is minor, over time the PVC sheath will weaken and the wire will begin to overheat, which will lead to a short circuit;
- If there is not enough wire length, a special coupling is used. To work with it you need some experience;
- By the marking you can find out the parameters of the product and what it consists of, which will be very helpful in your work;
When laying cables in grooves, you need to use corrugated tubes or cable channels that provide protection to the product from external influences.
Not only electrical specialists, but also cable product sellers and the average consumer need to be able to decipher the markings of cables and wires. This way, when purchasing, it will be easier to choose the right product. If the wiring is selected incorrectly, disastrous consequences can occur.
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.
Homemade fusible link from a conductor, selection by cross-section
Under no circumstances should you accept making your own fuse links FOR THE NORM. Installation of such products can be considered as a TEMPORARY MEASURE.
Diameters of COPPER wire for fuse link
| Diameter, mm | Current, A | Diameter, mm | Current, A |
| Ø 0.05 mm | 0.6 A | Ø 0.71 mm | 47.8 A |
| Ø 0.063 mm | 1.25 A | Ø 0.75 mm | 52 A |
| Ø 0.071mm | 1.5 A | Ø 0.8 mm | 57.2 A |
| Ø 0.08 mm | 1.8 A | Ø 0.85 mm | 62.7 A |
| Ø 0.09 mm | 2.1 A | Ø 0.9 mm | 68.3 A |
| Ø 0.1 mm | 2.5 A | Ø 0.95 mm | 68.6 A |
| Ø 0.112 mm | 3 A | Ø 1.0 mm | 80 A |
| Ø 0.124 mm | 3.5 A | Ø 1.06 mm | 87.3 A |
| Ø 0.14 mm | 4.2 A | Ø 1.12 mm | 94.8 A |
| Ø 0.16 mm | 5.1 A | Ø 1.18 mm | 102.5 A |
| Ø 0.17 mm | 5.6 A | Ø 1.25 mm | 111.8 A |
| Ø 0.18 mm | 6.1 A | Ø 1.32 mm | 121.3 A |
| Ø 0.2 mm | 7.1 A | Ø 1.4 mm | 132.5 A |
| Ø 0.224 mm | 8.4 A | Ø 1.45 mm | 139.7 A |
| Ø 0.25 mm | 10 A | Ø 1.50 mm | 147 A |
| Ø 0.28 mm | 11.8 A | Ø 1.6 mm | 161.9 A |
| Ø 0.315 mm | 14.1 A | Ø 1.7 mm | 177.3 A |
| Ø 0.335 mm | 15.5 A | Ø 1.8 mm | 193.2 A |
| Ø 0.355 mm | 16.9 A | Ø 1.9 mm | 209.5 A |
| Ø 0.4 mm | 20.2 A | Ø 2.0 mm | 226.2 A |
| Ø 0.45 mm | 24.1 A | Ø 2.12 mm | 247 A |
| Ø 0.5 mm | 28.2 A | Ø 2.24 mm | 268.2 A |
| Ø 0.56 mm | 33.5 A | Ø 2.36 mm | 290 A |
| Ø 0.63 mm | 40 A | Ø 2.5 mm | 316.2 A |
| Ø 0.67 mm | 43.7 A |
For repairing fuses with protection current from 0.25 to 50A
| Fuse protection current, Ampere | 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 | 0.01 | 0.02 | 0.04 | 0.07 | 0.10 | 0.18 | 0.20 | 0.25 | 0.32 | 0.39 | 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 current from 60 to 300A
| Fuse protection current, Ampere | 60 | 70 | 80 | 90 | 100 | 120 | 160 | 180 | 200 | 225 | 250 | 275 | 300 | |
| Wire diameter, mm | Copper | 0.82 | 0.91 | 1.00 | 1.08 | 1.15 | 1.31 | 1.57 | 1.72 | 1.84 | 1.99 | 1.14 | 2.20 | 2.40 |
| 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 | |
Maximum current for different thickness of copper wires
Table 1
(Data from table 1.3.4 PUE)
| Cross-section of current-carrying conductor, mm2 | Current, A, for wires laid | ||
| open | in one pipe | ||
| one two core | one three core | ||
| 0,5 | 11 | – | – |
| 0,75 | 15 | – | – |
| 1 | 17 | 15 | 14 |
| 1,2 | 20 | 16 | 14,5 |
| 1,5 | 23 | 18 | 15 |
| 2 | 26 | 23 | 19 |
| 2,5 | 30 | 25 | 21 |
| 3 | 34 | 28 | 24 |
| 4 | 41 | 32 | 27 |
| 5 | 46 | 37 | 31 |
| 6 | 50 | 40 | 34 |
| 8 | 62 | 48 | 43 |
| 10 | 80 | 55 | 50 |
| 16 | 100 | 80 | 70 |
| 25 | 140 | 100 | 85 |
| 35 | 170 | 125 | 100 |
| 50 | 215 | 160 | 135 |
| 70 | 270 | 195 | 175 |
| 95 | 330 | 245 | 215 |
| 120 | 385 | 295 | 250 |
The ratings of wires used in household electrics are highlighted. “One two-core” is a cable with two wires, one of them is Phase, the other is Zero. That is, this is a single-phase load supply. “Single Three-Wire” is for three-phase power supply.
This table shows at what currents and under what conditions a wire of a given cross-section can be operated.
A burning example from practice - if the socket says “Max.16A”, then you can lay a wire with a cross-section of 1.5 mm2 for this one socket . But be sure to protect the outlet with a circuit breaker for a current of no more than 13A, or better yet, 10A. On this topic, you can read my article About replacing and choosing a circuit breaker.
In the table, a single-core wire means that no more wires pass nearby (at a distance of less than 5 wire diameters). Two-core wire - two wires side by side, usually in one common insulation. This is a more severe thermal regime, so the maximum current is less. And the more wires in a cable or bundle, the less the maximum current for each conductor must be due to possible mutual heating.
I find this table not very convenient for practice. After all, most often the initial parameter is the power of the electricity consumer, and not the current, and based on this you need to choose a wire.
How to find the current knowing the power? You need to divide the power P (W) by the voltage (V), and we get the current (A):
I = P/U
How to find power knowing current? You need to multiply current (A) by voltage (V), we get power (W):
P = IU
These formulas are for the case of active load (consumers in residential premises, such as light bulbs and irons). For reactive loads, a factor of 0.7 to 0.9 is usually used (in industry where large transformers and electric motors operate).
I offer you a second table, in which the initial parameters are current consumption and power , and the required values are the wire cross-section and the tripping current of the protective circuit breaker.
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.
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 a wire of a suitable diameter (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!
Electrical copper wire
Manufacturing is carried out in accordance with GOST 434-78, from grade M1 or higher. It is characterized by a rectangular cross-section, with a thickness from 0.5 to 12.5 mm, a width from 2 to 35 mm. This copper wire can be purchased in the following grades: PMM (soft), PMT (hard). Produced in coils. Electrical round copper wire is used to make: cords, cables, wires, motor windings, etc.
At 20 ºС, the product has an electrical resistance: not exceeding 0.01724 Ohm•mm2 for MM brand products; 0.01780 Ohm•mm2 – for MT (Ø up to 2.44 mm inclusive); 0.01770 Ohm•mm2 – for MT (Ø above 2.44 mm).
For a product of the MM brand, the relative elongation is:
— Ø from 1.80 to 5.00 mm (inclusive) – 30%;
— Ø more than 5.00 mm – not less than 35%.
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.
Wire M1
M1 brand wire is considered the highest quality and most expensive. The purity of the copper alloy used for its production is 99.9%. Composition: Cu – 99.9%, impurities (such as Pb, Fe, Ni, S, As, Sb, Bi, Sn) – not higher than 0.1%. According to physical characteristics, there are: hard (M1T), soft (M1M). Other types of M1 wire: oxygen deoxidized (M1P), oxygen-free (M1B), phosphorus deoxidized (M1F), cathode (M1K).
Wire M1 differs from other rolled products (M2, M3) by increased performance characteristics, due to the minimum content of impurities in the material. It has good thermal and electrical conductivity. Bends well while maintaining strength properties. Nice appearance.
This wire is most often used in such areas as aircraft and shipbuilding, and electric power. They produce cords, cables, thermocouples, wires, and high-tech cryogenic equipment.
Operating principle of fuses
The principle of operation of disposable protective devices is very simple. Inside each of them there is a calibrated wire connecting the contacts. If the current value does not exceed the maximum permissible norms, it heats up to approximately 70 degrees. When the electric current exceeds the set rating, the heating of the wire increases significantly. At a certain temperature it begins to melt, resulting in a break in the electrical circuit. Wiring burnout occurs almost instantly. Because of this, fuses got their name - fuse link.
In different designs, the fuse link is selected in such a way that operation occurs at the set current value. During operation, fuses periodically fail and must be replaced. As a rule, they are not repaired, but many home craftsmen quite successfully restore them.
Since only the wire itself burns out, but the body remains intact, it is necessary to replace it and the device will continue to perform its functions. New technical characteristics are often not only not inferior to the old device, but also in many ways superior to it, since the quality of hand assembly is always higher than the factory one. The main condition is the correct choice of conductor material and calculation of its cross-section.
Properties
The main advantage of copper wire is its low resistivity. That is why it is actively used in the electric power industry and in the design of various electrical appliances. The production of wires is greatly facilitated by the high ductility of the metal. High-quality copper is easy to process in high precision mode. The alloy formula is selected individually in different cases, based on what target properties should be achieved. The melting point of pure copper is 1083 degrees Celsius or 1356 degrees Kelvin. And the density of this metal is 2.07 g per 1 cm3. Therefore, it is not difficult to calculate the mass over a cross section:
- with a thickness of 1.5 sq. mm. – 0.0133 kg per 1 m3;
- with a cross section of 4 sq. mm. – 0.035 kg per 1 m3;
- with a cross section of 6 sq. mm. – 0.053 kg per 1 m3.
Causes of blown fuses
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:
Fuse links. How to choose and calculate current. Operation and Application
Fuse links are electrical elements for protecting equipment from short circuits and overvoltage by turning off power when current load limits are exceeded. Opening the circuit occurs due to the melting of a safety wire of a certain thickness. Several types of these devices are known to the industry. They all differ in internal and external design features, but function according to the same principle.
Nowadays, in order to protect household electrical equipment, more practical reusable circuit breakers are used, but disposable fusible links are still found in plugs. They are especially relevant for premises of temporary and old buildings, where the installation of effective modern shields is not economically justified. In household appliances, there is still no alternative to the classic fuse.
Fuse links are also actively used in industry. The performance of an entire plant or utility network may depend on them. It is better not to buy industrial fuses secondhand, on the market or from unverified organizations. A wise decision is to turn to electronics professionals, for example, the online store Conrad.ru. In such matters, the miser pays not twice, but three times
Overview of species
Tinned copper wire is quite common. The point is that it is coated with tin using galvanic installations. The coating layer can vary from 1 to 20 microns, depending on the situation. However, on a specific product it is always the same. The tin layering increases wear resistance, allowing the use of thinner wire than usual. The service life of tinned products is much longer than that of uncoated wire. In addition, with such processing, basic technological characteristics are also improved. But it would be very reckless to evaluate the diameter only from the point of view of the durability of the material.
The thickness of the product directly affects its price. So, in many cases it is much more profitable to buy thin wire with a cross-section of 1 mm or 2 mm. But this is not always possible. To make wires, you also have to take into account the level of electrical resistance and resistance to heat. In many household appliances, it is even necessary to use copper conductors with a cross-section of 3 mm, 4 mm, and sometimes more. It all depends on how much current is to be passed through a particular circuit.
For hidden wiring and installation inside electrical appliances, thicker copper is needed than for external installation.
A serious problem for many DIYers and even industrial workshops is that insulated copper wire is extremely expensive. The price for enamel protection is especially high. Therefore, quite often they purchase “bare” metal and cover it with a layer of varnish insulation. But only trained specialists or real electrical engineering enthusiasts can cope with such work. Soft wire is obtained by annealing, and it is valued mainly where tying knots and bending metal are required.
But both hard and soft varieties of products can have:
- square;
- semicircular;
- flat section (it’s unnecessary to talk about a typical round one).
For rivets
Industrial users often purchase spools and drums of copper wire to make rivets. The diameter and length of these rivets vary greatly. In addition to pure copper, they are also used in various alloys, including those containing phosphorus. The peculiarity is that during molding they produce a base in the form of a cylinder and a cap in the shape of a semicircle. The size of the rivets varies greatly and must be selected individually. Rivet products are hollow, complemented by a washer, designed for grip or hammering.
Electrotechnical
This type of wire is used to make network wires and cables for electrical appliances. It is also used in the production of enamel-coated wires and network cables for the LAN protocol. The nominal diameter of electrical wire can be 1.15-4.5 mm. When shipping, coils placed in a box are sometimes secured with plastic tape. When sending wire in steel baskets, stretch film is wrapped around them.
For the electrovacuum industry
The wire intended for it is evaluated primarily by such an indicator as vacuum density. It is determined by the ability of specific parts and components to prevent the leakage of gases and the ingress of other substances from the outside. Therefore, special attention is paid to eliminating miniature cracks and hairlines. Problems can also be caused by pores and cavities that communicate with the external atmosphere. The use of metal containing impurities hazardous to the quality of the vacuum environment is strictly unacceptable.
That is why wire for the vacuum industry is produced with strict concentration control:
- zinc;
- cadmium;
- manganese;
- tin;
- phosphorus;
- bismuth;
- antimony and a number of other elements.
If we allow the presence of such impurities, then during the production of various products they will evaporate and create deposits on parts in the vacuum cavity. The maximum concentration of all harmful substances that can evaporate during the production of vacuum equipment is 0.0001%. Not only pure elements are taken into account, but also their oxides and oxides. The concentration of alloying additives is also strictly standardized, and it can vary very slightly in different heats within the same series.
The production of copper alloys with substances having a high melting point usually occurs by mixing the powders and then sintering them. In any case, there are only three key electrovacuum grades of copper - MV, MB, MVK. The presence of oxygen is also normalized - no more than 0.01% by weight. The copper-tantalum alloy is smelted in induction vacuum furnaces with minimal residual pressure.
Of course, only experienced engineers can choose a specific alloy and type of wire.
Welding
No matter how great the demand for copper wire is in the radio engineering industry, a much larger volume is still used for welding work. Since copper and alloys derived from it in the liquid state react violently with oxygen and hydrogen, they are used only in an atmosphere of inert gases. The best results are obtained by welding in helium and argon . But, for reasons of economy, nitrogen is often used - when used skillfully, it turns out to be no worse. Copper wire is used in both manual and semi-automatic welding, and in fully automated production.
Conventional gas welding with such wire is also sometimes used. But this is more typical for jobs that do not require special responsibility. Copper is useful for surfacing operations, when the treated surfaces are given special additional properties (wear resistance, corrosion resistance, and so on).
Welding products of foreign manufacture are marked according to the AWS standard (USA) or in accordance with EU requirements.
Important: it is worth distinguishing between copper filler and copper-plated wire. When a seam is created without special requirements for strength, commercial copper is used (for example, M1 products). It is recommended to brew constantan and cupronickel with copper-nickel additives. Here are some more matches:
- additives based on copper and nickel are suitable for bronze produced from aluminum;
- copper-silicon wire is used to work with silicon-copper, zinc-copper structures, as well as for electric arc welding of galvanized steel surrounded by argon;
- copper-tin wire is needed for electrical connection of tin-based bronzes in an inert environment;
- brass (L60-1, L63 and others) is needed to perform gas welding of brass and to deposit coatings on steel with a high carbon concentration.
We choose the diameter of the fuse wire - we analyze all the subtleties of the issue
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.
Transportation and storage
Rules for storing copper wire are regulated by GOST standards. Basic Rules:
- The optimal method of storage and transportation is the use of frame bays. For transportation, the coils must be packed in a special film. It will protect the material from adverse environmental conditions. In most cases, coils can be stored in a fold without packaging.
- The wire must be stored in special warehouses. The basic requirements for storage are low humidity, dry ventilation, minimal risk of prolonged wetting of the material (short-term wetting due to carelessness is allowed), and so on.
- Different grades of copper should be stored separately in the warehouse. If the wire becomes tangled during transportation, untangling is necessary. When unraveling, under no circumstances should the material be allowed to twist in a figure eight pattern.
How to determine the fuse rating from the case and on the board
Before you change something that has gone bad, you need to understand what has gone bad. In our case it burned out. Here you can rely only on the inscription on the board itself or on the fuse, because other methods of finding out what the fuse rating was are very unsteady and groundless. After all, a serviceable fuse will not show anything as zero resistance, but a faulty break. At the same time, do not send it to the laboratory for analysis in order to find out what kind of material it was. Let's look at examples of designation of fuses on the board and SMD elements. By the way, sometimes even a resistor can be used instead of a fuse.
APPENDIX 1 Recommended
PURPOSE OF WIRE AND RODS
| Material grade | Purpose |
| M1, M1p | For automatic inert gas, submerged gas and gas welding of non-critical copper structures, as well as the production of electrodes for welding copper and cast iron |
| M2r | For gas welding of general purpose copper structures |
| MCp1 | For gas welding of critical and electrical structures made of copper |
| MNZHKT5-1-0.2-0.2 | For manual, semi-automatic gas-shielded welding of copper-nickel alloys, copper-nickel alloys and copper with bronze, brass and steel (carbon, alloy and corrosion-resistant), as well as surfacing on steel |
| MNZH5-1 | For the manufacture of electrodes for welding copper-nickel alloys with each other and brass and aluminum-manganese bronze |
| BrKMts3-1 | For manual gas-shielded welding of flexible copper structures and automatic submerged arc welding of copper |
| BrAMts9-2 | For manual gas-shielded welding of aluminium-manganese bronze, arsenic brass, copper and copper-nickel alloy with aluminium-manganese bronze; manual and mechanized surfacing on steel |
| BrKh0.7, BrHNT, BrNTsr | For manual argon arc welding of bronzes |
| BrKh0.7 | For automatic submerged arc welding of chrome bronze |
| BrAZhMts10-3-1.5 | For the manufacture of electrodes for aluminum-iron bronze welding and automatic submerged arc surfacing of bronze |
| BrOTs4-3 | For manual welding in shielding gases of copper; mechanized submerged arc welding of copper and brass |
| BrOF6.5-0.15 | For manual gas-shielded welding of tin phosphorus bronze and tin bronzes |
| L63, LS60-1 | For gas welding of brass and surfacing on carbon steel |
| LK62-0.5 | |
| LKBO62-0.2-0.04-0.5 | |
| LOK59-1-0.3 | |
| LMts58-2 | |
| LZhMts59-1-1 |
Calculation of conductors for fuses
where: d – conductor diameter, mm; k – coefficient depending on the conductor material according to the table.
where: m is a coefficient depending on the conductor material according to the table.
Formula (1) is applied for low currents (thin conductors d=(0.02 - 0.2) mm), and formula (2) for high currents (thick conductors). Odds table.
The conductor diameter for use in a fuse is calculated using the formulas: For low currents (thin conductors with a diameter of 0.02 to 0.2 mm):
For high currents (thick conductors):
The amount of heat generated at the fuse link is calculated by the formula:
where: I – current flowing through the conductor; R – conductor resistance; t – time the fuse-link is under current I.
The resistance of the fuse link is calculated by the formula:
where: p – resistivity of the conductor material; l – conductor length; s is the cross-sectional area of the conductor.
To simplify calculations, the resistance is assumed to be constant. The increase in resistance of the fuse link due to increased temperature is not taken into account.
Knowing the amount of heat required to melt the fuse link, you can calculate the melting time using the formula:
where: W is the amount of heat required to melt the fuse link; I—melting current; R is the resistance of the fuse link.
Wire drawing
For production at factories, a special casting technology is used, which makes it possible to obtain copper wire with a cross-sectional diameter of about 20-30 millimeters. This figure is quite high, since such a thick wire has a lot of disadvantages - high specific gravity, high resistivity of the material, and so on.
Therefore, after casting, drawing is also used. This technology allows you to reduce the diameter of the product to the required parameters (from 1-2 micrometers with ultra-fine drawing to 10 millimeters with coarse drawing). The drawing technology itself is quite simple: thick wire is passed through special holes (dies), the diameter of which is less than the diameter of the original wire.
Technology
Drawing requires special drawing machines, as well as adherence to a certain procedure.
- Immediately before drawing, the original wire must undergo an etching procedure. For this, a solution of hydrochloric acid is usually used, which is heated to low temperatures (40-50 degrees Celsius). After etching, it is also recommended to anneal the metal workpiece - this will make the metal fine-grained, which will allow for better drawing. After annealing, it is necessary to neutralize the remaining etching acid and rinse. Pickling and annealing can significantly increase the service life of drawing machines - if this is not done, the drawing holes-dies will quickly become clogged with scale, which will slow down the production process.
- Now you can proceed directly to drawing. To do this, the ends of the original wire are sharpened using forging tools, and then the wire is inserted into special die holes. After this, the engine of the drawing machine is started. To obtain thin or ultra-fine wire of small cross-section, it is successively passed through several dies.
- At the last stage of processing, the wire becomes quite rigid and springy. To get rid of this drawback, final annealing of the material occurs in the last compartment of the drawing machine. At the end, drying is carried out in special cabinet compartments - after this, winding is carried out on reels. Drawing is completed - the wire spools can now be placed in a warehouse and delivered to the customer using vehicles.
Automation
The drawing procedure is semi-automated - the operator only prepares and threads the initial wire, and the machine itself performs the drawing itself in automatic mode (although the operator can control the procedure parameters using the control panel).
In some cases, special lubricants can be applied before drawing - these can be fatty oils, emulsion inhibitors, solutions of alkaline salts, and so on. The purpose of applying a lubricant is to reduce friction during drawing - this allows you to obtain a thinner and more uniform wire + by applying a lubricant, the risk of ruptures is minimized.
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.
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.
Total views: 217755
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.
