Calculator
A
Steady-state current draw of your circuit
Determines inrush factor and fuse type
V
For voltage rating check
Standard fuse ratings — IEC 60127
| Rating | Type | Breaking capacity | Common housings | Typical use |
|---|
Fuse housing types
| Housing | Size | Max voltage | Max current | Notes |
|---|---|---|---|---|
| 5×20 mm glass | 5 × 20 mm | 250 V AC | 20 A | Most common in Europe. Transparent — condition visible |
| 5×20 mm ceramic | 5 × 20 mm | 250 V AC | 20 A | Higher breaking capacity than glass. Opaque body |
| 6.3×32 mm | 6.3 × 32 mm | 250 V AC | 25 A | Older US / industrial standard. Still common in Europe |
| Micro blade (ATM) | 10.9 × 3.8 mm | 32 V DC | 30 A | Automotive — compact. Colour-coded by rating |
| Mini blade (ATO) | 16.3 × 10.9 mm | 32 V DC | 40 A | Automotive standard. Colour-coded by rating |
| Maxi blade (APX) | 29 × 8.5 mm | 32 V DC | 100 A | Automotive — high current. Main fuse box |
| SMD 1206 | 3.2 × 1.6 mm | 125 V | 5 A | PCB mount. Replaceable or one-shot (non-resettable) |
| SMD 0805 | 2.0 × 1.25 mm | 125 V | 3 A | PCB mount. Compact low-current protection |
| PTC resettable | various | 30–60 V | 0.1–6 A | Resets after fault clears. Good for USB / battery protection |
Selection guide
Fast (F) vs Slow-blow (T)
- Fast (F) — blows quickly on any overcurrent. Use for sensitive electronics, semiconductors, PCB protection
- Slow (T) — tolerates short inrush surges. Use for motors, transformers, switching supplies
- Medium (M) — compromise. General purpose, lamps, heaters
- When in doubt with motors: choose T (slow-blow)
Rating rule of thumb
- Fuse rating = 125–150 % of max operating current
- Always round up to the next standard value
- Motor inrush can be 6–10× normal current for 50–200 ms
- Switching PSU inrush: 3–5× for a few milliseconds
- Fuse must blow before any component is damaged
Voltage rating
- Fuse voltage rating must be ≥ supply voltage
- Do NOT use a 32 V automotive fuse on 230 V AC
- DC fuses are different from AC fuses — arc quenching differs
- Glass fuses: typically rated 250 V AC
- Blade fuses: typically 32 V DC (automotive)
Automotive colour codes (blade)
- ■ Red — 10 A
- ■ Blue — 15 A
- ■ Yellow — 20 A
- ■ Violet — 3 A
- ■ Orange — 5 A (mini) / 40 A (maxi)
- ■ Green — 30 A
- ■ Pink — 4 A