This section provides an overview for glass fuses as well as their applications and principles. Also, please take a look at the list of 7 glass fuse manufacturers and their company rankings.
Table of Contents
A glass fuse is a fuse that uses glass as the protective tube.
They are the most commonly used tube fuses. Fuses are safety components that interrupt current flow by melting the element when an overrated current flows through them. Continued flow of current in excess of the rated value can cause accidents such as circuit breakage, smoking, ignition, and so on.
Glass fuses are widely used in instrumentation and control equipment.
The following are examples of glass fuses in use:
They are most often used in control circuits, etc. Since glass fuses are small and space-saving, they are used for overcurrent protection on circuit boards. They are also used in main indicator lights and control power supplies because they operate faster than general breakers.
Glass fuses consist of a glass tube, an element, and a cap.
The glass capillary is the part used to protect the filament. PC glass is used as the material in most cases. Features of the glass capillary are that it is made of transparent glass, and it is possible to visually check whether the filament inside is fused or not.
Depending on the product, an arc-extinguishing agent is sealed in the glass fuses. The arc-quenching agent is a material that suppresses the generation of arcs when the filament breaks, and is mainly made of silica sand.
The element is the part that fuses in the event of overcurrent. Generally, the thicker the element, the higher the allowable current, and the difference can be seen visually when looking inside from the glass tube. Zinc is often used as the material. Other than zinc, elements are fabricated with lead, silver, or other alloys, the melting point of which is adjusted by blending.
Elements are made of metals with low melting points, such as those mentioned above, and melt when the temperature reaches the melting point due to Joule heat generated by electric current. The user's intended fuse melting characteristics can be obtained by varying the element composition, heat dissipation, and heat capacity.
The mouthpiece is the part that is connected to the fuse receiving part called the fuse holder. The material used is nickel-plated copper. Information such as withstand voltage and allowable current is generally printed on the mouthpiece.
There are three types of glass fuses: normal fusing type, time-lag fusing type, and quick-acting fusing type. Each glass fuses are further classified into Class A and Class B, respectively.
Type A and B fuses have different fusing characteristics, and Type A is the mainstream fuse in the U.S. and is currently not widely used in Japan.
The normal-flow fuse is a common glass fuse. These fuses are capable of withstanding 200% of the rated current for about 2 minutes. Glass fuses used in telecommunications equipment and control power supplies are mainly of the normally blown type.
Time-lag fuses are fuses that have a large time lag when they blow. Time-lag blown glass fuses are used when inrush currents or start-up currents are large. These fuses are used to protect motors and solenoid valves.
Fast-blow glass capillary fuses are designed to shut off excessive currents instantaneously, and will shut off in about 0.5 to 1 second when about 200% of the current flows through them. They are used to protect semiconductors that are at risk of failure due to excessive or reverse currents.
Glass fuses are connected to a fuseholder. The fuseholder has a pawl or spring that holds the capacitor in place. Since there is a risk of electric shock if the fuseholder is touched when removing the fuse, a special jig is used to ensure safety.
The capacity of the glass fuses used must be greater than or equal to the rated current of the electrical component. However, it is also important to select one with a capacity less than the maximum capacity of the wiring or weakest component. Attention must also be paid to the withstand voltage, and there are two types, one for 125 V and the other for 250 V.
*Including some distributors, etc.
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