Fuse Code Reference
Cross-reference blade fuse color ↔ current + the meaning of fast/slow-blow letters.
What it does: Cross-reference blade fuses by color or current, and look up fuse speed letters like F/T.
When to use it: When replacing an automotive fuse, identifying an unmarked fuse, or reading a fuse spec.
Disclaimer: This result is a reference estimate. For actual production, refer to the device datasheet / local regulations as authoritative.
Blade fuses identify their current by a color code? — pick one side to look up the other.
MEANS —
⚠ Color is only for quick identification; when replacing a fuse, always match the current and speed characteristic, go by the marking on the body / the vehicle manual, and never increase the current.
Blow speed letters (IEC 60127, common on glass/ceramic tubes)
| Letter | Name | Notes |
|---|---|---|
| FF | Very fast-acting | Fastest blow time; protects highly sensitive devices such as semiconductors. |
| F | Fast-acting | Quick-blow; common in general-purpose electronic circuits. |
| M | Medium time-lag | Between fast-acting and time-lag. |
| T | Time-lag | Slow-blow; tolerates start-up inrush, used for motors / transformers / power supplies. |
| TT | Very long time-lag | Longest delay; withstands very large surge currents. |
No history yet. Each calculation is automatically saved to this device.
How to use the fuse code reference
Cross-reference by color/current → look up the speed letter → replace with the original rating.
- 01
Recognize blade fuse colors
Automotive blade fuses have standard colors by current rating (e.g. 10A red, 15A blue). Select a color or an amperage to look up the other.
- 02
Read the fast/slow-blow letters
Glass-tube/ceramic-tube fuses are printed with letters like
F(fast-blow) /T(time-delay) — the table below explains each letter's blow speed. - 03
Replace with the original rating
Always replace with a fuse of the same current and speed characteristic; the color only helps with quick identification.
Blade fuse color ↔ current (standard)
ATO/ATC regular, mini, and low-profile mini share the same color code.
| Current | Color | English |
|---|---|---|
| 1 A | Black | black |
| 2 A | Grey | grey |
| 3 A | Violet | violet |
| 4 A | Pink | pink |
| 5 A | Tan | tan |
| 7.5 A | Brown | brown |
| 10 A | Red | red |
| 15 A | Blue | blue |
| 20 A | Yellow | yellow |
| 25 A | Clear/White | clear |
| 30 A | Green | green |
| 40 A | Orange | orange |
SAE J1888 / ISO 8820 / DIN 72581.
Common questions, answered in 3 minutes
Can F and T fuses be interchanged?
Not arbitrarily. F (fast-blow) protects sensitive electronics; T (time-delay) tolerates the startup inrush of motors/power supplies. Using fast-blow in place of time-delay causes frequent nuisance trips, while using time-delay in place of fast-blow protects too slowly.
Which do I trust if the color and printed current disagree?
Go by the marking printed on the fuse body. Color is an industry convention, and a few manufacturers or special types may differ.
Why is 25A clear/white?
This is the standard color-code convention (25A=Clear/Natural). It indeed has no vivid color and is distinguished by being clear.
Do large Maxi fuses use this same color set?
No. This table is for standard blade fuses (regular/mini/low-profile); Maxi and high-current fuses ≥50A use a different color code, so check the corresponding spec.
Can I substitute a higher-current fuse?
Absolutely not. The fuse current must match the circuit design; increasing it only lets the wiring overheat and catch fire during a fault, defeating the protection.
Standards and sources referenced by this tool
| Item | Value / Formula | Source |
|---|---|---|
| Blade color code | SAE J1888 / ISO 8820 | Automotive blade fuse |
| Blow characteristic letters | FF/F/M/T/TT | IEC 60127 |
Color is for reference identification; when replacing, always go by the marking on the fuse / the equipment manual.