Micro Fuses
Useful information about fine fuses
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What are fine-wire fuses?
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How are fine-wire fuses structured?
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How does a micro fuse work?
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What fine fuses are available at Conrad?
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Micro fuse table
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FAQ – Frequently asked questions about fine-tuning
What are fine-wire fuses?
Fuses are used to protect components of electrical/electronic installations from damage or destruction . For this purpose, a fuse is connected between the power supply and the module to be protected. If a current that is higher than the allowable current flow through the fuse flows into the protected assembly due to an internal fault, the fuse disconnects the assembly from the power supply . This protects not only the module, but also other components that are connected to the same power supply.
It can be separated by bimetal switches, self-resettable fuses and circuit breakers. In the case of fine fuses, a fuse wire in the fuse housing heats up so much through the current flow from a certain value that it melts and thus interrupts the current flow galvanically. This type of interruption is irreversible and can only be remedied by replacing the fuse. Fine-wire fuses have the advantage that they interrupt the current flow and do not damage adjacent electrical components due to their encapsulated design. This behavior is committed up to a defined current and is described with the term switching capacity.
Fine-wire fuses can be removed from the bracket to intentionally interrupt the current flow for repairs.
Another term for fine-wire fuses is device protection fuses with the common abbreviations GS or G fuses.
How are fine-wire fuses structured?
This special type of fuse consists of two connections in the form of metal caps that are attached to the ends of an insulating sleeve. The actual melting wire is located between the connections. The melt conductor consists of copper or silver-based material , optionally with different coatings. The diameter of the hot-melt wire essentially determines the nominal current of a fine fuse.
The metal caps of the fuse are taken by specially shaped holders, which simultaneously establish the electrical connections between the power source and the fuse on one side, and the fuse and the assembly to be supplied on the other. For the protection of high currents, there are construction versions with screw lugs .
The insulating body can be made of glass or ceramic. There are fine fuses with melt wire embedded in the insulating body or exposed to quartz sand.
Two sizes have been established: In Europe, 5 millimeters in diameter and 20 millimeters in length, in the USA, ¼ inches in diameter and 1 ¼ inches in length (6.3 x 32 millimeters). Different fine fuses have been designed for special applications and usually higher loads.
For the identification of the fine fuses, there are embossing on the metal caps which provide information about the rated current and voltage, the tripping characteristic, the breaking capacity and, under certain circumstances, the so-called melting integral. The information may also be printed on ceramic bodies. Color coding is less common.
How does a micro fuse work?
In normal operation, the fine-wire fuse flows through the nominal current at rated voltage. If the current rises to a defined multiple of the rated current within a defined time, the melting wire passes from the solid state to the liquid state to the gaseous state and interrupts the power supply . This may result in an arc that is immediately extinguished by embedding the melt wire into quartz sand.
The time elapsed from the exceeding of the maximum permissible current to the destruction of the hot-melt wire is the current-time characteristic of a fuse . This characteristic is used to distinguish between fine fuses in the response behavior of " super-time" via " time-lag " (between 100 and 300 milliseconds), " medium-time " (between 50 and 90 milliseconds) and " quick-acting " (less than 20 milliseconds) to " super-fast ". Fine-wire fuses must have a specific tripping behavior defined by standards, such as EN or UL. This means that they can withstand higher current loads for a promised period of time without triggering. The value for this is the melting integral, which is calculated from current and time. For example, fuses that protect motors or transformers must be able to withstand the inrush current without addressing.
What fine fuses are available at Conrad?
In our shop you can choose from the following technical selection criteria for fine-wire fuses in addition to new products, customer evaluations and brands (manufacturer):
- Diameter from 2.06 millimeters to 2.69 centimeters. This also makes special designs available for special applications.
- Length from 5.72 to 85 millimeters
- Nominal current from 0.032 to 600 amps
- Rated voltage from 32 to 3,000 volts
- Trigger characteristic: All five as described above
- Fuse structure: Transparent glass tube or with extinguishing agent, ceramic tube without and with extinguishing agent, with and without display bolt, with screw lugs
- Contents of packaging from 1 to 1,000 pieces, the latter as economical industrial packaging
- Category: A distinction is made here between DC, high-voltage, multimeter, time delay, UL and fine fuses as well as between fuse sets.
The production of fine-wire fuses must comply with limit values for substances that are hazardous to health and that are hazardous to the environment. With the usual term RoHS, almost all fine fuses are offered by Conrad.
Micro fuse table
In order to keep the number of possible fuse values manageable, fine-wire fuses are manufactured in different degrees. The following tables R5, R10 and R20 show the basic series of the standard number according to DIN 323.
R5 series
1.00
1.60
2.50
4.00
6.30
10.00
R10 series
1.00
1.25
1.60
2.00
2.50
3.15
4.00
5.00
6.30
8.00
10.00
R20 series
1.00
01:12
1.25
1.40
1.60
1.80
2.00
2.24
2.50
2.80
3.15
3/55
4.00
4.50
5.00
5.60
6.30
7.10
8.00
9.00
10.00
FAQ - Frequently asked questions about fine-tuning
What must be observed when handling fine fuses?
- Fine-wire fuses are part of electrical installations and electronic devices which must only be handled by trained personnel.
- In some cases, fine-wire fuses are installed within devices. Improper opening of such devices by unauthorized persons may void an existing warranty.
- Before replacing a faulty fuse, the cause of the tripping must be determined to avoid further defects on the modules. For this purpose, use the measuring and testing technology offered by Conrad in a wide variety of applications.
- Always replace fine fuses with models with the exact identical electrical parameters to protect the elements behind them from damage.
- The so-called patching of fuses with aluminum foil or wires is prohibited. This can lead to the destruction of equipment and personal injury caused by it, serious liability consequences.
- Note also the "derating": This describes the property that the possible nominal current load decreases as the ambient temperature increases. These values can be taken from the data sheet if required by technical requirements.
How do defective micro-fuses become noticeable?
- Visibly separated melting wire for glass bodies
- Outlet of a visual bolt for special designs
- Total power interruption
- Voltage and current fluctuations due to loose fixing of fine fuses