Published On: Sun, Sep 4th, 2022

Questions with answers from the knowledge of electrical materials and the practice of electrical installations – 1

Questions with answers from the knowledge of electrical materials and the practice of electrical installations – 1

Author: Radoje Jankovic

In this paper, I will present several practical questions from the knowledge of electrical installation material and its application in the execution of electrical installations in various facilities. In order not to theorize too much, I will base myself on describing the pictures in as much detail as possible, because that’s the easiest way to learn than when you just listen to a dry lecture in class. It was said long ago by smart people thata picture is worth more than 1000 words.

Of course, I will not go in school order, because in practice we will never meet in that way.

I will try to show this issue with as many examples as possible of performing different electrical installations and using various electrical materials and electrical devices. I think that in this way I will bring the practice closer to students of master schools and students of electrical engineering schools and colleges, as well as to many fellow beginners, electricians, electrical technicians, electrical engineers, and why not designers. The same benefit will come to heads of construction sites, foremen on construction sites, supervisory authorities on the execution of electrical installations and examiners who perform technical acceptance and issue appropriate certificates for the facility where the electrical installation was performed.

Ok, enough talk!

Let’s get down to the nitty-gritty.

I think it is more interesting and interesting than stories.

Fusible fuses in the protection of low-voltage electrical installations

Properly and strictly according to regulations and standards, the electrical installation is the most important element in the area of ​​protection of people and property both at work and in daily use, i.e. exploitation of electrical installations, electrical devices and electrical equipment. The contractor or the owner of the electrical installation of any purpose is obliged to carry out complete, regulations-specified tests of the buildings used for living and work in order to determine their safety and security. This work is performed by an authorized and certified expert or an institution that deals with this issue, which issues a certificate for the electrical installation and every electrical device, which confirms the complete correctness of the electrical installations.

The protection of conductors from unauthorized loading, whether intentional or accidental or short-circuit, is solved by using fuses that are placed at the beginning of each line in the direction of current arrival, that is, from the main low-voltage busbars.

If a switch is placed in the electrical installation, right next to the fuse, it is advised to place the fuse behind the switch because then the fuse is changed when the switch is open and is not energized (Figure 1). When using automatic switches, the fuse must be placed behind this switch. It should be emphasized here that the designer of the electrical installation defines the places of switches and fuses for all consumers that are connected to low-voltage busbars in distribution cabinets, strictly respecting technical regulations at the local level and international standards that deal with the field of all types of electrical installation in practice. Protection is performed for a two-wire network, two-pole or one-pole. For a three-phase system, the neutral conductor is not protected unless it is emphasized by the corresponding regulation for the purpose of the electrical installation in question.

The fuse performs the function of protecting the conductor by interrupting the electric circuit in which it is placed. This interruption of the electrical circuit can be achieved by melting the fusible insert in the fuse, by electromagnetic action or by thermal action of the bimetallic strip.

According to the method of breaking the electric circuit, fuses are divided into fusible and automatic fuses.

According to IEC and other valid standards, fuses in installations must be designed so that the interruption of the electric circuit is carried out in a closed space, without the possibility of fire, with a visible indicator of the interruption of the electric circuit and in such a way that the irreplaceability of the current is ensured, i.e. the impossibility of closing the electric circuit past the fuse. Today, fusible fuses with auxiliary so-called fuses are produced. signal contact that immediately gives a signal that the fuse has reacted.

Basic nominal characteristics of the fuse

The nominal voltage of a fuse is the lowest value of the nominal voltage of all its parts (fuse body, gauge ring, fuse cap, fusible insert). This means that the rated voltage of the fusible link may be different (higher) than the rated voltage of the fuse holder in which the fusible link will be used.

The standard values ​​of the rated fuse voltages are:

• for the DC voltage supply system: 110, 125, 220, 250, 440, 460, 500, 600, 750 V

• for AC voltage supply system: 120, 208, 220 (230), 240, 277, 380 (400), 415, 480, 500, 600, 660 (690) V

The rated currents of fusible fuses are: 2, 4, 6, 8, 10, 12, 16, 20, 25, 32, 40, 50, 63, 80, 100, 125, 160, 200, 250, 315, 400, 500, 630, 800, 1000 and 1250 A.

The rated current of the holder (also called the base) of the fuse must be selected from the range of rated currents of fusible inserts, unless otherwise specified by special standards for a particular type of fuse.

Time-current characteristics are given for melting durations longer than 0.1 s. Current is represented on the abscissa, and time on the ordinate. A logarithmic division is used for both coordinates. The time-current characteristics of the fusible insert depend on the construction, as well as, for a particular fusible insert, on the ambient air temperature and cooling conditions. If not specified, it is understood that the characteristics refer to an ambient air temperature of 20 °C. In connection with the operation of the fusible fuse insert, the rated time and rated current are defined. They differ in this:

• nominal non-melting current ( I nf ) – determined current value, which the fusible insert can withstand during the determined (nominal) time without melting, and

• nominal melting current ( I f ) – determined current value that causes the action of the fusible insert during the determined (nominal) time.

The rated breaking power (current) of a fusible link is the value (effective for alternating current) of the expected current that the fuse can break for a specified voltage under specified conditions. The rated breaking current is given by the manufacturer in relation to the rated voltage. The value of the minimum rated breaking current is determined in special standards for a certain type of fuse.

Installing the fuse

The fuse must not be placed in the circuit of the neutral conductor of single-phase or multi-phase circuits.

In TN power supply systems, a fuse as a protective device against overcurrent that serves as protection against indirect contact by automatically switching off the power supply, must be installed at the beginning of each current electric circuit (output from low-voltage busbars) as well as in all places where the cross-section of the conductor is reduced.

In IT power supply systems, a fuse as an overload protection device, when the exposed parts are connected to each other in the event of another fault, must be installed at the beginning of each current electric, as well as in all places where the cross-section of the conductor is reduced.

Branches from cable and overhead low-voltage networks are secured when entering the network.

Classification of fuses

According to the way of breaking the electric circuit in the fuse, they are divided into: fusible and automatic.

Classification of fusible fuse inserts (cartridges).

The fusible insert (the element that is replaced after the fuse has operated) is the part of the fuse that must melt when the fuse operates. In practice, the old designations of fusible cartridge-insert fuses (abbreviated: fuses) are still widely used. According to IEC and other applicable standards, fuses are, in general, divided according to:

• construction, i

• performance characteristics.

Division of fuses according to construction (fusible installation fuses)

Protection of conductors against short circuit (overload), i.e. the short-circuit current is generally carried out in such a way that the chosen place of the conductor is deliberately weakened by inserting a piece of thin wire. This thin wire melts before the shielded conductor reaches an unacceptable temperature.

This wire is made of silver, zinc, or another metal or alloy. Under load, this wire heats up and melts, which is why this type of fuse is called a fusible fuse.

In terms of construction, fusible fuses are made as:

• type D installation fusible fuses, which are called installation fuses with a thread,

• type B installation fuses, also called blade fuses,

• miniature fuses, which are directly installed on some receivers, and

• low-voltage fuses with high breaking power, which are also called installation high-performance fuses or NV-fuses.

1.Fusible fuses

From the name of these cigarette lighters, it is clear that their main part, which can be a wire or a tape, melts and thus interrupts the electric circuit. Since the melting is done at a high temperature, it is necessary to ensure a closed fireproof space where the melting will be carried out, so that the high temperature is not transferred to the environment, which can be flammable. These requirements are met by porcelain (in various variants), and the inner space is filled with quartz sand and can be lined with an inlay made of some durable insulating material. This housing is called a cartridge or cartridge, several types are shown in the following figures. Other insulating parts of the fuse are also made of porcelain. However, it should be noted here that the insulating parts of the fuse can be made of some other high-quality insulating materials.

Several types of fusible links are produced, such as:

– miniature,

– standard,

– high performance (High Capacity Rupturing – HCR fuses).

3. Bases for fusible fuses

The base, body or base of fusible fuses is made of porcelain. The fuse body is produced for voltages of 500 and 750 V or more depending on the manufacturer and for currents from 2 to 200 A. The contact elements of the fuse are with Edison thread of the fuse, which is clearly visible from the pictures, and there are three versions of these bases, namely:

UZ – elements, in which the connection of the conductor is made from the front and are rectangular in shape, which can be seen in pictures 1, 2,  3,  4.  and  5.

Slika 1. Porcelansko postolje osigurača UZ-25
Figure 1. Porcelain fuse holder UZ-25
Slika 2. Porcelansko postolje osigurača UZ-63
Figure 2. Porcelain fuse holder UZ-63
Slika 3. Presek kroz UZ – osigurač. Gde je: odvod =  outgoing phase wire, dovod = incoming phase wire, rastalni uložak = fusible link, glava = head, kontaktni vijak = contactin screw, rastalna nit = fusible link.
Figure 3. Section through UZ – fuse. Where is: odvod = outgoing phase wire, dovod = incoming phase wire, kontaktni vijak = fusible link, kontaktni vijak = contactin screw, topljiva nit = fusible link.
Slika 4. Pogled sa zadnje strane UZ – osigurača
Figure 4. View from the back of the UZ fuse
Slika 5. Izgled sa strane UZ – osigurača
Figure 5. View from the side of the UZ – fuse

TZ – elements (casings, bases) in which the conductor connection is made from the back of the distribution board or mounting base in the distribution board. They are square in shape as can be seen from the pictures below.

TZ – elements are used for mounting on distribution boards from the front or back. On the front, distribution boards are placed if the board is made of insulating material, e.g. of pertinax or marble. If it is divisible, i.e. mounting plate made of sheet iron and accessible from the back, are placed from its back, and not directly on the plate, but on a pertinax base that is attached to the cabinet structure with screws.

UZ – elements ie. fuse bases are placed on metal distribution – mounting plates in the same way as TZ – bases, except that their base can be made of iron sheet or profiled iron.

Slika 6. Presek kroz TZ – osigurač. Gde je: odvod =  outgoing, dovod = incoming, rastalni uložak = fusible link, glava = head, kontaktni vijak = contactin screw, rastalna nit = fusible link.
Figure 6. Section through TZ – fuse. Where: odvod = outgoing, dovod = incoming, topljivi uložak = fusible link, glava = head, kontaktni vijak = contactin screw, spacer thread = fusible link.

EZ – elements are shown in the following pictures that clearly show the construction. EZ – elements are mounted in cabinets made of sheet iron or cast iron, e.g. main household household fuses when connecting houses or buildings to the low-voltage network. These cabinets are waterproof and dustproof. Later, I will also show examples from the practice of domestic and residential connection cabinets to the external, aerial or underground cable low-voltage network.

In the element-base of the fuse, a copper or brass contact thread of the Edison type is fixed with one or two connecting screws for the TZ element, or one clamp for the UZ and EZ elements. The central (central) contact of the base is connected to the second screw, or clamp. To that screw (clamp) must always be connected the phase conductor that comes from the low-voltage network buses, that is, from the electric meter, while the contact screw must be connected to the phase conductor that goes from the fuse to the electrical devices, i.e. the poor. Therefore, the contact thread of the fuse base can come under voltage only when the fuse is complete, i.e. when the fusible insert (cartridge) is placed in the base and the fuse head is screwed as shown in Figure 6.

In this way, people who would come into contact with the contact threads of the fuse when the fuse is open are not exposed to voltage hazards.

Fuse base elements are made for currents of 25 A, 63 A, 100 A, and rarely for higher currents.

The contact thread of the elements for 25 A and 63 A is a pressed Edison thread, and for the element 25 A it is Edison-normal E 27 (as for lamps with tungsten filament up to 200 W), and for the elements 63 A it is the thread E 33. For the elements of 100 A, the contact threaded element is made on a lathe (cut thread) because the aim is to achieve a better

contact between it and the groove of the fuse head, so that due to possibly too much transient resistance between them, both threads would not heat up excessively, which could even cause them to be welded. In that case, the fuse could no longer be opened, so a new one would have to be put in its place. That substitution would take away

a lot of time and materials.

On the back side, the fuses can have oblong recesses, which can be seen in pictures 7.  and 30.

Slika 8.  Pogled sa donje strane na topljivi TZ – osigurač
Figure 8. Bottom view of fusible TZ – fuse
Slika 9. Pogled sa strane na topljivi TZ – osigurač. Natpisna pločica = Name plate
Figure 9. Side view of fusible TZ – fuse.
Natpisna pločica = Name plate
Slika 10. Element topljivog EZ – osigurača
Figure 10. Element of fusible EZ – fuse

Here we will show several types of fuse holders. Of course, there are other forms and types depending on the purpose and manufacturer.

Slika 11.  Postolje osigurača EZN-25 A sa zaštitn pločom
Figure 11.  EZN-25 A fuse base with protective plate
Slika 12. Postolje osigurača EZN-63 A sa zaštitnom pločom
Figure 12. EZN-63 A fuse base with protective plate
Slika 13. Postolje osigurača EZN-25 A bez zaštitnog prstena-poklopca
Figure 13. Fuse base EZN-25 A without protective ring-cover
Slika 14. Porcelansko postolje topljivog osigurača EZ 25 A sa zaštitnim prstenom, zove se i držač zaštitne ploče
Figure 14. Porcelain fuse holder EZ 25 A with protective ring, also called protective plate holder
Slika 15.Element topljivog EZ – osigurača
Figure 15. Element of fusible EZ – fuse
Slika 16. Porcelansko postolje osigurača sa zaštitnim prstenom EZN-63 A
Figure 16. Porcelain fuse base with protective ring EZN-63 A
Slika 17. Postolje EZN 63A sa poklopcem za topljive osigurače
Figure 17. Base EZN 63A with cover for fusible fuses
Slika 18. Jednodelno postolje D02 sa poklopcem
Figure 18. One-piece stand D02 with cover
Slika 19. Postolje EZN 3x25A trodelno sa poklopcem 25A
  Figure 19. Base EZN 3x25A three-part with cover 25A
Slika 20. Porcelanska kapa DII 6-25 A sa Edisonovim navojem
Figure 20. Porcelain cap DII 6-25 A with Edison thread
Slika 21. Porcelanska kapa DIII 35-63 A sa Edisonovim navojem
Figure 21. Porcelain cap DIII 35-63 A with Edison thread

D type fusible fuses

Type D fuses are used in household electrical installations and devices for voltages of 220, 240, 380 and 415 V (according to the IEC standard) exclusively for direct or exclusively alternating or both types of current, and for currents up to 200 A.

They are often called installation fuses. They are made in two basic forms for connection from the front and from the back. Each of these shapes has four basic parts: the base, the calibration ring, the insert and the cap. According to the IEC standard and other valid standards, four sizes of fuse bases are made for four values ​​of nominal currents, namely:

• D II,

• D III,

• D IV, i

• D V.

The size of the fuse is determined by the size of the base.

The base D II is made for a current of 25 A.

The base D III is made for currents up to 63 A, which is why it has slightly larger dimensions.

The base DV is made for nominal currents up to 100 A.

According to purpose or shape, the following fuse bases are distinguished:

• base for connection from the front (universal base or UZ) – It is used for distribution panels (panels) with schematics on the front surface, and holes for supply conductors are drilled on the panel.

• base for connection from the rear (TZ base). It is used for distribution boards when the connection is made behind the board.

• base for installation, e.g. in various appliances for households, in switchboards, etc.

• base for overhead line. It is used for household connections.

The calibration ring is a replaceable part of the fuse base. According to IEC standards, the calibration ring is a part of the fuse that serves to prevent interchangeability. The calibration ring has the height of the rated voltage and rated current marked on the upper surface. This surface is painted with the prescribed color corresponding to the rated current.

Also, the fusible inserts are marked with the colors shown in the previous pictures, which correspond to the color of the calibration ring. Colors should prevent the insertion of fusible inserts with a higher rated current than that corresponding to the ring mounted in the holder (base).

Standard colors used to mark fuses

Characteristic data for type D fuses

Current irreplaceability is a design feature of type D fuses, which prevents contact between the insert and the calibration ring at the base of the fuse if the calibration ring is intended for a lower current than the rated current of the insert. This is achieved in such a way that D-type fuse inserts for higher currents have a wider tip and cannot be inserted into a fuse sized for lower current, whose calibration ring is smaller in diameter than the tip of the insert. However, it is possible to insert a fusible insert with a lower rated current into a fuse designed for higher currents. This type of replacement is not dangerous.

The designation D in the name of installation fuses indicates that current irreplaceability is achieved by using different diameters, (D), calibration ring and insert neck.

The selectivity of the fuse is the property of the fuse to always blow before the next fuse for the rated current of the next stage. For example. the 10 A insert must burn out before the 16 A insert.

Safety against short circuit is the property of the fuse to withstand the short circuit current in the electric circuit in which the fuse is located without mechanical and thermal destruction of the fuse elements.

The breaking power is the power with the highest current that the fuse can break under the rated voltage and with the highest current, without causing mechanical and thermal destruction of the fuse elements, as well as without a permanent arc and flame outbreak. The breaking power current is significantly lower than the short-circuit current. It is from 4 to 16 kA, while the short-circuit currents are from 250 to 12,000 A.

Type B fuse

Type B fuses are calibration fuses, consisting of two cylindrical caps and a fusible insert (as seen in the pictures). The standard nominal voltage of these fuses is 250 V, nominal currents: 5; 10; 16; 31.5 and 63 A.

The pictures show several type B fuse inserts.

They are made for alternating current only. Current irreplaceability is achieved by specific dimensions of the cap for each value of rated current.

The melting current of the insert for these fuses is 2.5 × In, while the operating time is from 16 to 28 seconds depending on the value of the rated current of the insert.

A fusible insert of a certain rated current cannot be replaced with a fusible insert of a higher rated current without replacing the cap. Live parts are not accessible to touch when the fuse base is installed and connected for normal use and supplied with fusible link and cap.

4. Fusible insert-cartridge

Soluble insert ie. the cartridge (the element that is replaced after the fuse has operated) is the part of the fuse that must be melted when the fuse operates.

The soluble insert consists of:

– insert bodies,

– contact caps,

– refractory fillings,

– fusible wires or tapes.

As can be seen from the pictures below, the body of the cartridge is made of porcelain in the form of a hollow cylinder, the interior of which serves as a closed refractory space in which the tape or wire is melted in the event of a short circuit or overload, as well as extinguishing the arc.

The contact caps are made of metal that conducts electricity well, and they are used to close the upper and lower openings of the body of the insert. The upper cap serves for a direct connection with the drain, and the lower one with the supply of the phase conductor of the electric circuit, which is protected by a fuse against a short circuit.

The refractory filling inside the cartridge is, in fact, quartz sand that is placed inside the body in which there is a fusible tape or wire. Quartz sand makes it possible to interrupt a large current during a short circuit without transferring the arc from one contact cap to another.

The fusible tape is perforated and has the addition of a reactive substance that conditions the melting characteristic of the tape, which is slow at first, and very fast in the area of ​​high currents. This tape is not sensitive to short-term overloads that occur in electrical installations, and especially in electric drive. Silver is used for the tape as well as for the wire because of its good electrical conductivity.

Slika 22. Topljivi umetak D, 6 A
Figure 22. Fusible insert D, 6 A
Slika23. Topljivi umetak D, 10 A
Figure 23.  Fusible insert D, 10 A
Slika 24. Topljivi umetak D, 35 A
Figure 24. Fusible insert D, 35 A
Slika 25. Topljivi umetak D, 63 A
Figure 25.  Fusible insert D, 63 A
Slika 26. Topljivi umetak DIII 63A, gL/gG
Figure 26. Fusible insert DIII 63A, gL/gG
Slika 27. Topljivi umetak DIV 80A
Figure 27. Fusible insert DIV 80A
Slika 28. Topljivi umetak DIV 100 A
Figure 28. Fusible insert DIV 100A, 500 V, gL/gG
Slika 29. Topljivi umetak NEOZED, 20 A
Figure 29. NEOZED fusible insert, 20 A

2. Gauge (Calibre) rings or another name, contact screw

The gauge (calibre) ring is a replaceable part of the fuse base. According to IEC standards, the gauge ring is a part of the fuse that serves to ensure the irreplaceability of the provided cartridge and is made for all rated currents separately. For the correct functioning of the fusible link, a gauge ring is not needed much, because e.g. fuses of the older version did not have a contact screw (ring). He, however, has a very important task to prevent the insertion of a fusible cartridge for a stronger current than the one for which the electric circuit is intended and designed. The gauge ring has the height of the rated voltage and rated current marked on the upper surface. The rings are made of porcelain or steatite, and there is a contact at the bottom of the ring, i.e. connecting screw that screws into the support of the supply contact. The upper surface of the ring is painted with the same standard color as the fusible insert indicators corresponding to the rated current. The following pictures show the layout of the gauge rings for some rated currents of the exhauster.

Slika 30. Kalibarski prsten topljivog umetka (patrona) 6 A, 500 V, zelene boje
Figure 30. Gauge ring of fusible insert (cartridge) 6 A, 500 V, green color
Slika 31. Kalibarski prsten topljivog umetka (patrona) 10 A, 500 V, crvene boje
Figure 31. Gauge ring of fusible insert (cartridge) 10 A, 500 V, red color
Slika 32. Kalibarski prsten topljivog umetka (patrona) 16 A, 500 V, sive boje
Figure 32. Gauge ring of fusible insert (cartridge) 16 A, 500 V, gray color
Slika 33. Kalibarski prsten topljivog umetka (patrona) 20 A, 500 V, plave boje
Figure 33.  Gauge ring of fusible insert (cartridge) 20 A, 500 V, blue color
Slika 34. Kalibarski prsten topljivog umetka (patrona) 35, 500 V, crne boje
Figure 34. Gauge ring of fusible insert (cartridge) 35, 500 V, black color
Slika 35.  Kalibarski prsten topljivog umetka (patrona) 50A, 500 V, bele boje
Figure 35. Gauge ring of fusible insert (cartridge) 50A, 500 V, white color
Slika 36. Kalibarski prsten topljivog umetka (patrona) 63 A, 500 V, bakarne boje
Figure 36. Gauge ring of fusible insert (cartridge) 63 A, 500 V, copper color

Other ring colors for standard rated currents are:

In = 25 A, yellow color

In = 80 A, silver color

In = 100 A, red color

In = 125 A, yellow color

In = 160 A, copper color and

In = 200 A, blue color.

Cylindrical fuses

Slika 37. Cilindrični osigurač 22X58 GL/GG 63 A
Figure 37. Cylindrical fuse 22X58 GL/gG 63 A
Slika 38. Cilindrični osigurač 14×51 mm, GB 16 A
Figure 38. Cylindrical fuse 14×51 mm, GB 16 A
Slika 29. Cilindrični osigurač 10×38 mm, gG
Figure 39. Cylindrical fuse 10×38 mm, gG

Type N fuses

It is a fuse consisting of two bases and a fusible insert with “knife” contacts. They belong to the category of fuses handled by professionally qualified persons (fuses for industrial application), because the fusible inserts are accessible and can only be replaced by qualified persons. Mutual irreplaceability and protection against accidental contact of live parts do not have to be ensured by construction.

Division of fuses according to performance characteristics:

A. Normal (quick) fuses

According to IEC standards, the operating time of normal breakaway inserts must be shorter than the values ​​listed below:

Also, the operating time of normal fusible inserts must not be less than 10 s, with a test current 1.75 times higher than the rated current. When switching on electric motors, the current when starting asynchronous motors with a short-circuited rotor reaches 4 to 8 times higher than the rated current.

With increasing rotation speed, the current decreases at first gradually, then suddenly. The time it takes for the motor to reach full speed, i.e. the time it takes for the starting current to reach the rated value, depends on the design and type of motor. It amounts to about 0.35 s for an unloaded engine, and for a normally loaded engine it increases to about 0.5 s, while for engines with a larger mass, which should be brought to the rated speed, the time to reach full speed is much longer, about 1 s.

From this consideration, it is observed that a fast-blow fuse, whose rated current has a value close to the rated current of the motor, will inevitably blow before the starting current drops to the rated current value, which is why a stronger fuse must be selected or other means must be used to make the fuse withstand the starting current , for example. by choosing a fuse for starting the engine. A stronger fuse entails the replacement of a conductor with a larger section, which again leads to insufficient utilization of the conductor.

From the above, it can be concluded that quick inserts have a disadvantage that they do not allow good utilization of the conductor section. Better use of conductors is achieved by choosing slow and inert inserts.

B. Slow fuses

According to the IEC standard, the operating time of slow fusible inserts must be longer than the values ​​given in the previous table. Also, the operating time of the fusible inserts must not be longer than 6 s, with a test current 5 times higher than the nominal one.

The use of slow inserts comes into consideration due to the following phenomena: if a larger lighting load is switched on or an electric motor occurs, an electric shock occurs. In the first case, an electric shock occurs due to the lower resistance of the filament in a cold state. This difference in resistance reaches a tenfold value, which is why when the light bulb is turned on, a current ten times higher than the nominal value appears, and when the fiber glows, it suddenly drops to the nominal value. The duration of this shock current is less than a tenth of a second, but it is enough to melt the fuse wire. This means that a quick-release insert cannot secure an electric lighting circuit if its rated load matches the rated current of the fuse. Because of this, it is necessary to choose an insert for a stronger current, and therefore the section of the conductor, which already had a sufficient dimension, must be increased. and now it is increased only because of the insert for higher current. From this, it can be concluded that the conductor is unused, because a larger section was taken due to a larger fuse, and this was taken in a larger dimension to ensure the simultaneous inclusion of a larger lighting load.

Knife or power fuses

High breaking power fuses or high performance fuses with knife contacts.

The development of distribution networks leads to high-power networks in various industrial plants. In those installations, there is a need for the fuses to be significantly above 200 A, as well as for the breaking power to be higher.

These dimensions require a different construction of fusible fuses than the one developed for installation fusible fuses. This requirement was met by the development of fusible fuses with high breaking capacity. Their fusible insert insert has the shape of a tube, usually rectangular, so they are also called “tubular fuses”.

These fuses consist of two parts:

– carrier or stand and

– fuse cartridge.

As you can see from the pictures below, the fuse base consists of a basic porcelain or steatite plate and contact forks with connection clamps. With the help of two screws, it is attached to the corner or U-iron support or to the mounting board in the cabinet.

The fuse holder is made in several sizes – according to the rated current of the fuse – for currents of:

100 A, 160 A, 250 A, 320 A, 500 A, 800 A and even larger ones.

We can see the cartridges of these fuses in the pictures, and they have a cylindrical or square ceramic body, in which there is a fusible tape, fixed to knife contacts. Each of these contacts is attached to the ceramic body by means of a metal cap.

Cartridges are made for nominal currents:

10 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A, 100 A, 125 A, 160 A, 200 A, 250 A, 320 A, 400 A, 500 A , 630 A, 800 A, 1000 A, 1250 A.

These chokes are mounted on switchboards in larger and larger plants. They have a sluggish characteristic, which makes them very suitable for securing electric circuits, in which occasional long-term overloads occur, e.g. due to the commissioning of asynchronous electric motors with a short-circuited rotor (slip-ring AC motors).

A special isolating lever is used to replace the fuse.

Because of their high breaking power, these fuses are also called “high-efficiency fuses”, they are marked with “NV” low-voltage high-efficiency. According to IEC and other standards, these fuses are used for voltages of 220, 380, 400, 500, 600 and 900 V and for currents in the range of 2 to 1250 A.

Slika 40. Postolje nožastog osigurača 160 A
Figure 40. Base of knife fuse 160 A
Slika 41. Postolje nožastog osigurača 160 A
Figure 41. Base of knife fuse 160 A
Slika 42. Postolje nožastog osigurača NH I 250A
Figure 42. Base of knife fuse NH I 250A
Slika 43. NVO trostruka postolja (fuse rail)
Figure 43. NVO triple base (fuse rail)
Slika 44. Postolje nožastog osigurača NH 00, III 160A tropolno
Figure 44. Base of knife fuse NH 00, III 160A three-pole
Slika 45. Topljivi patron-umetak nožastog osigurača NVT-00 20 A, gL/gG
Figure 45. Fusible cartridge-insert of knife fuse NVT-00, 20 A, gL/gG
Slika 46. Topljivi patron-umetak nožastog osigurača NH0GG, 50 A
Figure 46. Fusible cartridge-insert of knife fuse NH00GG, 50 A
Slika 47. Topljivi patron-umetak nožastog osigurača NH00, 125 A
Figure 47. Fusible cartridge insert of knife fuse  NH00, 125 A
Slika 48. Rastavljač za nožaste osigurače
Figure 48. Disconnector for blade fuses

Fusible ultra fast fuses

The following figures illustrate several types of ultra-fast fuses according to the IEC standard in electronic devices for short-circuit protection. These fuses are usually placed in series with diodes and thyristors.

Slika 49. Cilindrični topljivi ultra brzi osigurači
Figure 49. Cylindrical fusible ultra-fast fuses
Figure 50. SITOR fuse link, with female thread on both sides, NH2, In: 1000 A, aR, Un AC: 690 V, Un
Slika 50. SITOR ultrabrzi osigurač sa urezanim navojem na obe strane , NH2, In: 1250 A, aR,
Slika 51. SITOR ultrabrzi osigurač sa urezanim navojem na jednoj strani i vijkom sa navojem, 630 A, 600 VAC, 500 V DC, 200 kA
Figure 51.  SITOR 630 A, 800 VAC, 500 V DC, 200 kA, Single-Sided Tapped-Thread, Screw-In Ultrafast Fuse
Slika 52. SITOR ultrabrzi osigurač bez noževa sa urezanim navojem, In: 450 A, aR, Un AC: 800 V, Un
Figure 52. SITOR ultra-fast fuse without knives with slotted thread, In: 450 A, aR, Un AC: 800 V, Un
Slika 53. SITOR ultrabrzi osigurač za šrafljenje na postolje , NH000, In: 400 A, aR, Un AC: 690 V,
Figure 53. SITOR ultra-fast screw-on fuse, NH000, In: 400 A, aR, Un AC: 690 V,
Slika 54. Ultra brzi nožasti osigurač aR/630A/690V
Figure 54. Ultra-fast blade fuse aR/630A/690V, Indikator: Top fuse status indicator

Slika 45. Ultra brzi nožasti topljivi osigurač gS, 100 A, 690 V, 100 kA
Figure 45. Ultra-fast blade fuse gS, 100 A, 690 V, 100 kA
Slika 46. Ultra brzi nožasti topljivi osigurač gS, 160 A, 690 V, 100 kA
Figure 46.   Ultra-fast blade fuse gS, 160 A, 690 V, 100 kA
NH1 gS NH Semiconductor fuse link
IEC/EN 60269-1, IEC/EN 60269-4, RoHS Compliant
Slika 47. Ultra brzi nožasti topljivi osigurač gS, 450 A, 690 V, 100 kA
Figure 47. Ultra fast blade fusible link, gS 450 A, 690 V, 100 kA
Slika 48. Ultra brzi nožasti topljivi osiguračgS, 630 A, 690 V, 100 kA
Figure 48. Ultra-fast blade fusible link, 630 A, 690 V, 100 kA
Slika 49. Postolje za nožasti topljivi osigurač, gS, 690V AC, 550V DC
Figure 49. Stand for blade fuse, gS, 690V AC, 550V DC
Slika 50. Dimenzijska skica topljivog nožastog osigurača
Figure 50. Dimensional sketch of fusible knife fuse
Figure 51. t-I characteristics
Slika 51. I-t karakteristika
Figure 52. Cut-off characteristics
Slika 52. Karakteristike isključivanja osigurača

Note: The photos are from various manufacturers catalogs. Drawings from my arhive.

About the Author

- Radoje - Rade Jankovic Electrician, Electrical Technician, Electrical Engineer, PhD, Ecologist, Environmentalist, Designer, Educator, Investigator... Today PROFESSIONAL TECHNICAL WRITER AND DOCUMENTATOR Massive practical experience in almost all fields of electrical engineering over 40 years. My International education group in Facebook: EEEW - ELECTRICAL & ELECTRONIC EDUCATION WORLD where published more than 8000 small or bigger articles, lessons, technical advice, projects, technical calculations, test questions with and without answers, illustrated test questions with and without answers; all my original works and few thousands of may original photos from practice, drawings, circuit diagrams, environmental lessons and examples from everyday practice etc., etc.

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