Miniature fuses. Fuse resistors with particular overcurrent protection
1Key Takeaways
Scope This part of IEC 60127 applies to specific overcurrent protection fuse resistors with a rated voltage of 500 V AC or 500 V DC, used for the safety protection of electrical appliances, electronic products and their components in printed circuit boards and other substrate systems. It does not include fuse resistors…
2Expert Interpretation
An in-depth look at BS EN IEC 60127-8:2018, the international standard for fuse resistors with specified overcurrent protection, covering ratings, test methods, safety requirements, and implementation recommendations. Suitable for printed circuit protection designs, it provides technical specifications for a minimum fusing characteristic of 16 times the rated power dissipation and a 35A interrupting capacity.
Analysis of the Standard's Core Content
BS EN IEC 60127-8:2018, part 8 of the IEC 60127 series of miniature fuses, specifically specifies the technical requirements for fusing resistors with specific overcurrent protection. This standard applies to printed circuit protection applications with a rated voltage not exceeding 500V AC/DC.
Definition of key parameters
| Parameter | Definition | Test conditions |
|---|---|---|
| Rated power consumption (P70) | Maximum continuous power consumption at 70℃ ambient temperature | 16 times power consumption impact test |
| Minimum fuse power consumption | 16 times rated power consumption value | 180℃ temperature rise limit |
| Rated breaking capacity | 35A@250V AC/DC | Power factor>0.95 |
Technological Evolution and Safety Requirements
The standard clearly distinguishes the core difference between traditional fuses and fusible resistors: the latter only has a fusing function within a specific overcurrent range (≥16 times the rated power consumption) and must be used in conjunction with overload protection devices. Key safety requirements include:
- Fire rating: GWIT ≥ 775°C/GWFI ≥ 850°C (plastic material)
- Creep distance: Classified according to rated voltage, up to 500V requires 6.9mm
- Dielectric strength: 2 times rated voltage for 1 minute
Test method specifications
Typical test process:
- Use a test circuit board that complies with IEC 61249-2-7
- Apply 16 times the rated power dissipation at an ambient temperature of 70°C
- Monitor terminal temperature ≤ 180°C
- Verify 35A breaking capacity (AC/DC)
- Insulation resistance ≥ 0.1MΩ (disconnection point)
Implementation recommendations
Design Considerations:
- Must use an overload protection device
- Preferably choose the E12/E24 series resistors
- Surface mount devices require consideration of pad thermal design
- Critical resistance calculation: Rcrit=Umax2/P70