Yes, fuses do indeed fail. Although they are designed as reliable and predictable fuse elements, in some cases they may not function as expected, resulting in failure.
There are two main forms of fuse failure:
Continuous interruption: This is the most dangerous type of failure.
Reason:
Aging: This is the most common cause. Over time, the performance of the metal melt (conductor) inside the fuse will decrease due to the following reasons:
Oxidation/Corrosion: Exposed to air, moisture, or corrosive environments, the surface of the melt oxidizes or corrodes, resulting in a decrease in effective cross-sectional area and an increase in resistance. This may lead to premature melting (misoperation) of the melt below the rated current, or more seriously, after long-term slight oxidation, the melt requires higher temperature (i.e. higher current) to melt, resulting in failure to melt in a timely manner during actual overcurrent or short circuit.
Metal fatigue/creep: Long term exposure to currents close to the rated value (even if not overloaded), or frequent cold and hot cycles (equipment on/off), can cause microstructural changes (fatigue) or slow plastic deformation (creep) in the metal melt. This will change its melting characteristics, making it unable to melt in a timely manner when needed.
High temperature environment: Installing fuses in high-temperature areas will reduce their actual load-bearing capacity. The higher the ambient temperature, the smaller the current required for the melt to reach its melting point (which may lead to false breakage), but at the same time, long-term high temperatures can accelerate aging and oxidation processes.
Insufficient overload level or short duration: Some types of fuses (especially slow melting type) have a tolerance for brief small overloads. If the overload current does not reach the minimum energy value required for melting, or the duration is not long enough, the fuse may not melt. But this is usually not a failure, but a design characteristic.
Selection error: The rated current of the fuse used is much higher than the actual requirements of the circuit. When overcurrent or short circuit occurs, the current may not be sufficient to blow the excessive fuse.
Poor quality products: using fuses that do not meet specifications or have poor manufacturing quality.
Physical damage: The fuse is mechanically damaged during installation or transportation (such as small cracks in the internal melt), but has not yet been disconnected, resulting in a change in its melting characteristics.
Consequence: If the circuit or equipment loses overcurrent protection, it may cause the wires to overheat, catch fire, or cause serious damage to the equipment (such as burning components).
When it should not be disconnected:
Reason:
Aging: Similarly, aging and oxidation can increase the resistance of the melt, causing it to generate more heat than designed at normal rated current. Long term accumulation or slight overload may cause it to melt.
High ambient temperature: As mentioned earlier, high temperature can significantly reduce the actual carrying capacity of fuses, causing them to melt at rated current or even below rated current.
Current surge: Although slow melting fuses are designed to withstand surge currents (such as surges during motor start-up or switch on power supply start-up), if the surge current is too large or lasts too long, exceeding the fuse's capacity (I ² t value), it can also cause the fuse to melt. This may be due to improper design selection or circuit abnormalities.
Mechanical vibration: Continuous severe vibration may cause fatigue fracture of the melt, especially on fuses with fragile or aged structural designs.
Installation issues:
Poor contact/excessive contact resistance: Poor contact between the two ends of the fuse and the clamp, resulting in heating at the contact points. This part of the heat will be transferred to the melt, causing it to melt when the current is lower than expected.
Excessive installation torque: When tightening the screw type fuse, excessive force may cause deformation of the internal structure or damage to the melt.
Voltage issue: Although fuses are mainly sensitive to current, the arc generated at the moment of melting may be difficult to extinguish under high voltage, causing the fuse to explode or continue to arc, resulting in "disconnection". The main reason for choosing a fuse with a rated voltage lower than the operating voltage of the circuit is.
Selection error: The fuse used has a rated current that is too low to withstand the normal operating current or expected surge current of the circuit.
Poor quality products.
Consequence: Causing equipment to shut down without reason, causing inconvenience or production losses (requiring troubleshooting and replacement of fuses).
How to reduce the risk of fuse failure:
Correct selection:
Rated current: Choose a fuse slightly larger than the maximum normal operating current of the circuit (usually recommended to be 1.1-1.5 times, refer to design specifications for details). Consider the impact of surge current and choose between fast melting or slow melting types.
Rated voltage: must be equal to or greater than the maximum operating voltage of the circuit.
Breaking capacity: It must be greater than or equal to the maximum fault current (short-circuit current) that may occur in the circuit.
Type: Choose the appropriate type based on the application (fast melting, slow melting, ultra slow melting, high temperature type, surge proof type, etc.).
Consider environmental factors: In high-temperature environments, it is necessary to choose fuses with higher rated current or specialized high-temperature fuses, and use them with reduced ratings (refer to the manufacturer's provided rating curve).
Correct installation:
Ensure that the fuse holder is clean, free from oxidation and deformation.
Tighten the screw type fuse according to the manufacturer's recommended torque.
Ensure good contact.
Use high-quality products: Choose manufacturer products with good reputation and compliance with relevant safety standards (such as UL, IEC, CCC, etc.).
Regular inspection and replacement: For critical equipment or equipment operating in harsh environments, even if the fuse is not blown, regular replacement should be considered according to the manufacturer's recommendations or practical experience to prevent failure caused by aging. If the same fuse frequently blows, it is necessary to thoroughly investigate the root cause of the circuit fault, rather than simply replacing the fuse with a larger amperage.
Summary:
Fuses are not permanent components, they will age over time and under usage conditions (current, temperature, environment), and may eventually fail. The most common failure mode is performance degradation caused by aging, manifested as "continuously breaking when it should be" or "breaking when it should not be". The correct selection, installation, environmental control, and regular maintenance are key to ensuring the reliable operation of fuses. Never ignore a blown fuse, look for the root cause; Similarly, we should also be vigilant about the hidden risks that aging fuses may bring.