How to Choose a Tube Fuse
Tube fuses have long been a conventional circuit protection device. They are dynamic circuit protectors with a wide range of applications across various industries, as they are constructed from various materials and come in varying sizes.Three electrical specifications must be considered when selecting the appropriate tube fuse: nominal current, voltage, and interrupting rating. This applies to all other fuses as well. Furthermore, in applications where the fuse is required to withstand short-duration, high-current pulses, the nominal melting point should also be examined.
Fuse Sizes and Usage
Automotive Fuses
Glass tube fuses are currently utilized in automotive accessory applications (12V) and are typically found in older-model North American vehicles. In the early stages of the development of automobiles and fuses, manufacturers developed their own customized components to meet the evolving requirements of their customers. Over time, the standardization of components began to establish itself, and new fuse sizing system was implemented.AG Fuses
The "AG system" of fuse sizing, which is abbreviated as "Automotive Glass," encompasses a range of dimensions, including length, diameter, and amperage classification. A matrix of dimensions is provided below, which cross-references the common AG size to the corresponding dimensions:
SFE Fuses
The "SFE system" sized fuses are always 1/4" in diameter and are engineered to meet the specifications established by the Society of Fuse Engineers. The length of the fuse is contingent upon the current rating, with a range of 5/8" for a 4A to 1-7/16" for a 30A. This ensures that the fuse is replaced accurately.
Consumer Electronics
Glass and ceramic tube fuses conveniently safeguard appliances and consumer electronics. Fuses are the preferred protection method due to their accuracy, small size, and reliability, as many appliances lack the capacity for larger, more expensive circuit protection devices. These fuses are frequently designated in millimeters rather than inches, as they are utilized extensively worldwide, including in regions beyond North America.Glass and ceramic tube fuses intended for electronic/electrical applications are rated at 125 V or higher. There are four sizes of user-replaceable fuses: 3.6 x 10 mm, 5 x 15 mm, 5 x 20 mm, and 6.3 x 32 mm.
Note:
- 5 x 15 mm easily replaces the 2AG size fuse
- 6.3 x 32 mm fuses are equivalent to 3AG (1/4” x 1 1/4”)
Fuse Response Time
It is helpful to understand overcurrent when discussing fuse response time. Overcurrents usually fall into one of two categories: overloads or short circuits. Short circuits are made up of extremely high currents that can endanger both equipment and people. Overloads usually happen when too many devices are added to a circuit, exceeding its normal rating.Sometimes, transient overloads are inevitable, such as when a motor starts up or when a circuit is first energized. Generally lasting between 1 and 5 seconds, these overload circumstances subside as the motor reaches its operational speed, or the circuit is fully powered.
Sometimes referred to as transient currents, these transitory overloads are typically 2 to 6 times the circuit's normal current. They are entirely normal but may result in complications if the overcurrent protection device is not correctly selected.
Fuse response times are introduced. In circuits that contain transient currents, it is recommended to employ a time-delay fuse (also known as a time lag or slow-acting fuse). A time delay fuse prevents a nuisance opening caused by the transient current condition by allowing the overcharge to exist for a few additional seconds before opening.
"Fast-acting" and "time delay" are exclusively used to describe transient currents and/or overloads. Both time delay and fast-acting fuses are extremely rapid when it comes to opening short circuits.
If fast-acting fuses are insufficient, there are also super-fast-acting fuses. Due to their super-fast action, these fuses are primarily employed to safeguard sensitive apparatuses, including rectifiers, SCRs, and transistors. Due to their exceptional performance, these fuses can be priced up to ten times that of conventional fast-acting fuses.
Ceramic vs Glass Fuses
Tube fuses are available in glass or ceramic. Ceramic fuses are stronger than their glass equivalents because of the physical characteristics of the ceramic material. Ceramic fuses use sand as a filling to enhance their effectiveness under short-circuit failures. The sand lets the fuse have more interrupting power by quenching the arcing. This indicates they can stop greater degrees of fault currents without causing harm.
In the event of a component deficit, it is possible to substitute a ceramic fuse for a glass fuse; however, this is not recommended. If a glass cartridge fuse is used as a substitute, the fuse envelope may rupture during a fault.
Note:
Glass and ceramic fuses can include an optional axial lead to the ends, allowing direct soldering onto the PCB. Axial-leaded fuses are often inexpensive and quick to install. However, this strategy limits future fuse replacements.
About the Author
OPTIFUSE manufactures the highest-quality fuses, holders, clips, fuse blocks, circuit breakers, resettable fuses, and accessories. In collaboration with their sister company, Switch Components, their manufacturing standards are to exceed and maintain high-quality and consistency levels and ensure that 100% of their products exceed the expected quality levels.