First, it must have DC fast-acting protection characteristics to rapidly interrupt severe overloads and short-circuit currents. Second, it must be compact, vibration-resistant, durable, and structurally interchangeable. Third, and most critically yet often overlooked, the fuse tube material must possess high-temperature resistance and be non-combustible and non-flammable.
Automotive high-voltage fuses operate long-term in enclosed, tight spaces without effective cooling. This is especially true when they share a closed, high-temperature environment with the battery pack. Improper material selection can lead to thermal melting and combustion of the fuse body. As the saying goes, "what makes you can also break you." To ensure comprehensive safety, the proper selection of automotive high-voltage fuses must be treated with the utmost importance and careful consideration.
Why Fuses are the Standard for EV Battery Protection
The use of high-voltage fuses for the main overcurrent protection of lithium battery systems in electric vehicles is, on one hand, based on the clear requirements of the national standard GB/T18384.1. More importantly, it's because when a severe overload or short-circuit fault occurs in the lithium battery system, a robust and reliable "gate" is needed to cut off and eliminate the extremely destructive short-circuit energy, effectively preventing the escalation and spread of high-voltage overcurrent accidents.
Due to the limited space in vehicles, it's impractical to install bulky and expensive DC circuit breakers. Therefore, using compact, relatively inexpensive, and easily installed DC fast-acting fuses as the main protection device to limit and interrupt abnormal electrical faults has become a recognized safety standard in the EV industry, both domestically and internationally.
A DC fast-acting fuse contains a pure silver element welded inside a tube filled with high-purity, compacted quartz sand. During normal operation, the fuse's own micro-ohm resistance is negligible. When the battery system experiences a severe overload or short-circuit current of several thousand amperes, the silver element and quartz sand work together to complete the entire "melting-arc extinguishing-interruption" process within milliseconds, absorbing and dissipating all the high-voltage surge current and high-energy heat within the fuse body.
During this process, the fuse tube must withstand the expansion pressure of 200-300 MPa generated by the internal high-voltage arc, as well as radiant heat exceeding 1000°C. If the tube material lacks sufficient high-temperature mechanical strength, it will rupture, explode, and eject an arc, leading to high-temperature carbonization and combustion.
The Hidden Danger: Organic Fuse Bodies
After 2014, with the significant growth in electric vehicle production and the increasing energy capacity of power batteries, the fatal flaw of using organic materials for fuse bodies began to be exposed in various incidents. Users reported multiple cases of fuse body combustion involving organic composite tubes, mostly occurring during the charging process of electric buses with systems over 500V.
Factors such as the battery's service life exceeding its warranty, the use of an organic material base for the fuse, loose conductive screws, or the fuse body being too close to the metal casing wall can all trigger accidental electric arcing and fire. Previously, due to incomplete information from accident sites and the reluctance of some vehicle and battery manufacturers to disclose details, issues like uncontrolled lithium battery overcharging leading to leakage, short circuits, and improper fuse installation were not deeply analyzed as root causes.
Why would an organic composite fuse body melt and ignite while the internal silver element and quartz sand remained largely intact? Where did this powerful short-circuit surge come from? These questions not only led to prolonged confusion and debate between suppliers and customers but also caused public doubt and anxiety about the safety of new energy electric vehicles.
In-depth research into the self-ignition phenomenon of organic fuse bodies revealed that the heat distortion temperature of organic composite materials is generally below 200°C. When operating for extended periods in the enclosed high-temperature environment of a battery or high-voltage box, especially when installed in a corner with poor ventilation, the material undergoes significant thermal aging. This leads to a gradual decline in both its mechanical and insulation strength.
Uncontrolled overcharging is particularly common in electric buses charging at high voltages (above 500V). The short-circuit surge resulting from battery leakage or capacitor breakdown due to overcharging can impact the relays and fuses in reverse, causing a rapid spike in the internal temperature. This accelerates the degradation of the organic tube. When the ambient temperature surpasses the material's melting point, the fuse body quickly carbonizes, turning the original insulating layer into a conductive one. The high-voltage surge then forms an external arc path along the tube wall, fiercely burning the organic material and causing it to self-ignite. This, in turn, ignites the electrical cables within the high-voltage box, leading to a full vehicle fire. According to eyewitnesses, the entire process can take just a few seconds, but the destructive energy is astonishing.
<Failure Sequence of an Organic Composite EV Fuse>
<Failure Sequence of an Organic Composite EV Fuse>This theory was finally confirmed by the investigation report on the "4.26" Shenzhen electric bus fire, released on August 9, 2015. A panel of 14 experts from the domestic EV, power battery, electrical, and charging fields concluded that "the accident was caused by power battery overcharging, leading to battery leakage, short-circuiting, and ultimately, fire." This finding revealed the deep-seated reason for the earlier incidents of fuse body combustion and serves as a vital lesson.
In almost all recorded incidents of fuse body combustion on electric buses caused by battery or capacitor overcharge short circuits, the scene is the same: an ultra-high-temperature arc spreads rapidly across the fuse body surface, not only melting the copper terminals but also capable of burning through a 5mm steel plate of the high-voltage box. This indicates temperatures exceeding 1200°C. In such an environment, an organic composite tube rated for only 200°C is instantly incinerated. Although remnants of the internal element and sand may remain, the fuse's protective function is completely lost.
Therefore, we conclude that as long as the BMS and charging pile management systems cannot achieve 100% effective control over lithium battery overcharging and over-discharging faults, using organic composite materials for high-voltage fuse bodies is not a scientifically sound or safe solution.
The Superior Solution: 95% Alumina Ceramic
<Organic EV Fuse Failure Before and After Incident>
A comprehensive safety survey conducted among more than 50 domestic EV and battery integration companies showed that 97% of users endorsed the "non-combustible tube" option, and 64% specifically approved of "high-strength ceramic tubes."
Based on this clear user preference for absolute safety, we at GONGFU Fuse made the decisive choice to abandon the organic composite materials we had used for eight years. Instead, we upgraded to high-insulation, high-temperature resistant, and non-combustible 95% Alumina (Al₂O₃ Corundum) Ceramic for our fuse bodies. With the absolute safety of electric vehicles as our primary goal, we have implemented this product upgrade across our mass production lines.
Table 1: Performance Comparison of Automotive Fuse Body Materials
| Tube Material | Heat Distortion Temp. (°C) | Flexural Strength (MPa) | Dielectric Strength (KV/mm) |
|---|---|---|---|
| Phenolic Molded Tube | 120-130 | 80 | 2 |
| Melamine Laminated Tube | 150-180 | 180 | 6 |
| Epoxy Glass Fiber Wound Tube | 120 | 290 | 10 |
| 95% Alumina Ceramic Tube | 1650 | 280-320 | 22 |
The reason our GFEFUSE brand fuses, including series 5H20L, 5H30L, 5H38L, H10H, H14FE, H14FA, 7H30L, 7H38L, 10H30L, and 10H38L, choose ceramic is proven by rigorous testing. During an arcing test, while the fuse terminals were damaged by the arc, the 95% Alumina Ceramic tube remained completely intact, withstanding the severe high-temperature trial. We have seen no cases of cracking, arc flashover, or combustion with our ceramic tube fuses, proving that choosing 95% Alumina high-strength ceramic is the correct and rational solution for manufacturing automotive high-voltage fuses.
Recent tests according to China's CCC mandatory safety certification showed a 500V/400A automotive high-voltage fuse completing the entire melt-arc-interrupt process in just 7.22 milliseconds when subjected to a 20KA short-circuit current. This fully confirms that ceramic tube fuses are not only high-temperature resistant and non-combustible but also possess exceptional performance, with a current limitation of 9.43KA and an arc-extinguishing time of 5.49ms.
A Final Recommendation for Safety
Following recent EV fire incidents, China's Ministry of Industry and Information Technology has issued notices for comprehensive safety hazard investigations. We hope that by reading this article, vehicle and battery manufacturers will pay high attention to the material structure and proper selection of high-voltage fuses during their safety checks. Do not assume that simply installing any fuse makes the system "insured" and safe; the investigation must begin with ensuring the fuse itself is "fire-proof."
<Ceramic Fuse CCC Short-Circuit Test Oscillogram>
We also recommend that battery manufacturers do not install high-voltage fuses inside the battery box. It is far better to isolate them in a separate, independent enclosure. This is not only safer but also more convenient for inspection and replacement, eliminating the need for frequent disassembly of the main battery pack. After all, once EVs are sold in large numbers, the people replacing these consumable parts will often be non-professionals.
About DONGGUAN GONGFU ELECTRONICS CO.,LTD.
As a dedicated developer and designer, GONGFU Electronics provides one-stop solutions for fuses, fuse holders, automotive fuses, automotive fuse holders, DC fuses, photovoltaic fuses, and energy storage fuses.