Common fuse formats
| Format | Size | Typical use |
|---|---|---|
| Glass 5×20 mm | 5 × 20 mm | Electronics, appliances |
| Ceramic 5×20 mm | 5 × 20 mm | Higher breaking current |
| 3AG (glass) | 6.35 × 32 mm | Older US equipment |
| Automotive blade (ATO) | ~19 mm | 12/24 V vehicles |
| Mini blade (ATM) | ~11 mm | Modern cars |
| MAXI blade | ~34 mm | High-amp automotive |
| MIDI / AMG | bolt-down | Battery mains, 30–200 A |
| Panel/plug fuse (NH) | various | Industrial AC distribution |
| SMD fuse | 1206 / 2410 | PCB-mount |
| Resettable (PTC) | through-hole/SMD | Self-resets when cool |
Speed classes (IEC)
| Class | Behavior | Use |
|---|---|---|
| FF — super fast-acting | Blows < 100 ms at 10× rated | Semiconductor protection |
| F — fast-acting | Blows < 1 s at 10× rated | Electronics |
| M — medium | Blows at 2× rated after a few seconds | General |
| T — time-delay (slow) | Tolerates inrush; blows at 2× eventually | Motors, transformers |
| TT — super time-delay | Very high inrush tolerance | Large motors, inrush-heavy loads |
Selection checklist
- Current rating: ~125–150% of steady load, well below wire ampacity.
- Voltage rating: must be ≥ circuit voltage. Fuses rated for DC are often lower than AC due to arc extinction.
- Breaking capacity (interrupting rating): ability to safely interrupt the maximum prospective fault current. Important on mains and batteries.
- Speed: slow-blow for motor/transformer inrush, fast for semiconductor protection.
- I²t rating: match to downstream device energy tolerance.
Was this article helpful?