Fuses can timely blow to disconnect the circuit and protect the product and circuit from damage when a fault occurs. However, many people worry about what happens if a fuse ages and cannot disconnect the circuit in time when a fault occurs. Today, I will teach you how to identify whether a fuse is aging and the hazards associated with aging fuses.
The UL standard specifies the maximum operating temperature at 75°C. Since the melting element of the fuse is quite sensitive to room temperature, its melting point and impedance will change under prolonged exposure to high temperatures. This change can affect the accuracy of the fuse, which is what we refer to as fuse aging.
Excessive Ambient Temperature
For standard fuse holders, when the temperature reaches approximately 160°C (150–170°C), tin begins to diffuse into the metal wire. The temperature at which the melting element starts to oxidize more vigorously is around 200°C (175–225°C). As the wire is oxidized from the outside in, along with multiple diffusions and thermal stress fatigue, the lifespan of the fuse will gradually shorten. Therefore, it is recommended that slow-blow fuse holders should not operate at temperatures above 150°C for extended periods, and standard fuse holders should not operate at temperatures above 175–225°C for extended periods.
Pulse Current
Pulses can create thermal cycles, which in turn lead to diffusion, oxidation, and thermal stress in the melting element. The fuse holder will also gradually age with the increase in pulse energy and frequency. The impact resistance lifespan of the fuse holder depends on the percentage of the pulse's I²t relative to the fuse's own I²t. Typically, this should be less than 20%, allowing the fuse to withstand over 100,000 pulses.
Contact Resistance
The contact resistance between the fuse holder and the terminal clamps, as well as the length and cross-sectional area of the connecting wires, can affect the fuse's lifespan. The contact resistance between the fuse holder and the terminal clamp should be less than 3 mΩ as per UL standards during testing. When the contact resistance is high, the terminal clamp generates heat instead of dissipating it, which is then transferred to the fuse.
What Safety Hazards Are Associated with Aging Fuses?
Answer: After a fuse ages, the normal operation of the circuit may sometimes cause the fuse to blow, which can easily disconnect the circuit and result in an inability to use electricity properly. If a self-resetting fuse ages, it may take a longer time to automatically reset after a fault occurs, or it may fail to reset at all.
Many electrical appliances and electronic devices in our daily lives are equipped with fuses to disconnect the circuit in the event of a fault. This not only protects the electrical equipment but also ensures the safety of individuals while using electricity. Therefore, it is important to regularly check the electrical devices, power circuits, and fuses in your home for signs of aging to avoid a number of potential hazards.
