Functions of Ceramic and Glass Electric Fuses

The following is a core technical analysis and selection guide for ceramic and glass electric fuses, compiled from authoritative information from multiple sources:

我. Core working principle‌
‌Fusing mechanism‌
‌Joule heat effect‌: When the current is overloaded, the heat generated by the conductor Q=0.24I2RtQ=0.24I2Rt exceeds the heat dissipation capacity, and the temperature rises to the melting point and melts.
‌Fusing curve‌:
1.3 times the rated current: melting time>1 小時
1.6 次: melting time<1 小時
8~10 times: instantaneous melting

‌Core function‌
Connected in series in the circuit, it cuts off abnormal current (overload/short circuit) by self-fusing to protect the equipment from burning or fire.

‌第二. Key parameters and classification‌
‌1. Current/voltage specifications‌

Parameters‌	Definition	Selection rules
額定電流 (In)	Maximum current value for continuous safe operation	Needs to be slightly larger than the circuit operating current (例如. 25A for a 20A circuit)
額定電壓 (Un)	The highest voltage that can be safely isolated after the fuse is blown	≥circuit operating voltage

2. Classification of fuse characteristics‌

‌Type‌	響應速度	‌‌Applicable scenarios	‌ Identification‌
Fast blow type	Millisecond level	Precision electronic equipment, semiconductor protection	FF（Fast Blow）
Slow blow type	Second level	Motor start, surge current circuit (such as car lights)	FM（Slow Blow）

3. Structural type‌

‌ 類型	‌特徵	Typical applications
Glass tube fuse	低成本, visible fuse status	Small household appliances, power adapters
Ceramic tube fuse	High breaking capacity, strong arc extinguishing	工業設備, electric vehicle battery packs
SMD熔斷器	小型化, SMT process	Mobile phones, laptop motherboards
Automotive chip fuses	Standardized color coding (such as red 10A, blue 15A)	Vehicle electrical system

第三. Selection and use points‌

‌Current matching‌
Calculation formula: ‌Rated current ≥ circuit operating current × 1.25‌ (safety margin reserved).
Avoid replacing low-current models with high-current fuses, otherwise the protection function will be lost.

‌Environmental adaptability‌
High temperature environment: select high-temperature resistant ceramic material (＞100℃ working conditions).
Vibration scenario: automotive fuses require impact-resistant structures (such as plug-in/bolt fixing).

‌Fault prevention‌
‌Poor contact‌: Fuse terminals oxidize and cause abnormal fusing, and regular inspection and tightening are required.
‌Pulse current‌: Slow-fuse type must be selected for scenarios such as motor starting.

‌Replacement specification‌
After fusing, it must be replaced with the same specification, and copper/iron wire short-circuiting is prohibited.

4. Typical failure causes

Fault phenomenon	‌Main cause	‌Solution‌
Frequent fuse	Load overload, short circuit or fuse rated current is too small	Check load power, Recalculate selection
Abnormal heating without fuse	Contact resistance is too large or poor quality fuse	Clean terminals and replace compliant products
Fuse when powered on	Short circuit in the circuit (such as line damage)	Check short circuit point and replace fuse after repair

5. Special type expansion ‌
‌Temperature fuse‌: responds to overheating rather than overcurrent, used to prevent overheating of electric irons and chargers.
‌Self-resettable fuse‌: impedance increases sharply after overcurrent, automatically resets after cooling, suitable for USB port protection.

‌Note‌: Fuses must be used in conjunction with circuit breakers, the former protects equipment, and the latter protects lines; high breaking capacity fuses should be used in ultra-high voltage scenarios (>600V).