Cartridge fuses have been produced for over 100 years and there is now an extremely large number in use throughout the world. They perform the vital duty of protecting equipment and electrical networks and ensure that the effects of faults, which inevitably occur, are limited and that the continuity of supply to consumers is maintained at a high level.
Not only electrical engineers, but nearly all members of the public are aware of the existence of cartridge fuses and the general impression is that they are simple devices in all respects. While it is true that their construction is not complex, they must be designed and manufactured with great care to ensure that they will perform as required.
What is a cartridge fuse?
Cartridge fuse is a fast type of safety device that is used to protect cables, power lines, and equipment against overloads and short circuits in electrical systems. The main function of a cartridge fuse is to protect systems and human life. Cartridge fuse is made of ceramic, porcelain, or glass.
Although they have left their places to miniature circuit breakers in recent years, they can still be used in electrical applications.
If you want to define cartridge fuses with different definitions you can use these:
- Cylindrical fuse
- Cylindrical fuse link
- Cartridge type fuse
- Glass cartridge fuse
- Mini cartridge fuse
How does a cartridge fuse work?
Cartridge fuse works according to the principle of conductor melting and must be replaced with a new one when it is blown.
There is a thin wire or metal alloy strip in the middle and two metal caps used as contacts when connected in series to an electrical circuit. It is designed to melt at a certain temperature when more current than the nominal amount of electrical current flows through the thin wire. When the wire melts, it becomes an open circuit, and no electricity flows.
Cartridge fuses are replaced inside a holder. This is called a cartridge fuse carrier or fuse holder.
Body and filling material of a cartridge fuse
The outer casing is made of ceramic to withstand pressure and thermal shock and has a high breaking capacity. Contact covers are made of silver-plated copper. Cartridge fuses filled with granular quartz of high chemical purity and grain sizes in the region of 300μm. The grain size is tailored to suit the element thickness and desired performance.
The filling material conducts some of the heat energy away from the fuse element to the body and therefore to obtain consistent performance it is necessary that the packing density of the filling material is maintained constant during production. This factor will have a very significant effect on the behavior at high current levels because a low packing density may allow the arcs to expand more rapidly, affecting the column voltage and thus the rate of current change.
Cartridge fuses have ferrule, blade, or screw-type methods of installation. They are made in capacities of 1 to 1000 amperes for voltages of 125, 250, 600, and 1000 volts. Fuses intended for 600 and 1000 volt service is longer and will not fit the same fuse holders as fuses intended for 250-volt service. Fuses of different ampere capacities are also designed for different sizes of fuse holders. For example, fuses of 1 to 30 amperes fit one size of the holder, and fuses with a capacity of 35 to 60 amperes fit a different size holder. Fuses above 60-ampere capacity have knife-blade contacts and are larger in diameter and length as the capacity increases.
Advantages of a cartridge fuse
Some benefits of cartridge fuse are:
- It has a high breaking capacity.
- There is no risk of reclosing after the trip.
- It has good selectivity values.
- Let through energy performances are high.
- It has a simple construction and compact size.
- It is easy to replace.
- It operates fast.
- It is a low-cost solution. (Check price)
- It can be used in low and high temperatures.
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Disadvantages of a cartridge fuse
Some drawbacks of cartridge fuse are:
- Risk of a one-phase trip on three-phase lines.
- Slow recovery time on a trip.
- Lack of accessories.
- Capable to perform only once. It needs to be changed after tripping.
- It is old technology.
- Most of them should be used with a fuse carrier.
Cartridge fuse types
There are two types of cartridge fuse available in the market:
gL or gG type
Quick cartridge fuses. It is designed for the protection of cables, lines, and equipment.
Slow cartridge fuses. They open with a time delay to withstand the starting currents of motors and transformers.
Let’s illustrate the difference between the two as follows:
Let’s say we have 1A gG and aM cylindrical fuse. This fuse should be exposed to a current of 10A. In this case, while gG type fuse blows in approx. 1 second, aM type fuse blows in approx. 2 seconds. This is the difference between them. Trip time curves for different current levels are detailed in the manufacturer’s catalogs. You should check them.
Cartridge fuse applications
Some applications of cartridge type fuses are:
- Automation and distribution panels.
- Protection of measuring instruments.
- Protection of isolated transformers.
- Protection of surge arresters.
- DC and solar applications.
- Motor starting applications.
Cartridge fuse sizes
The sizes of and maximum rated current for cylindrical fuses according to IEC 60269-2 are given below:
Colour codes of a cartridge fuses
Cartridge fuses have different colors such as:
- Pink: 2 A
- Brown: 4 A
- Green: 6 A
- Red: 10 A
- Grey: 16 A
- Blue: 20 A
- Yellow: 25 A
- Black: 35 A
- White: 50 A
- Copper: 63 A
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