Unlike automotive blade fuses, standard cylindrical cartridge fuses do not use a universal body-color-to-amperage code. If you are searching for a cartridge fuse color code, the answer depends entirely on the form factor and region. For UK mains plugs (BS 1362), the body color dictates amperage (Red = 3A, Brown = 13A). For industrial IEC/DIN fuses, the color is a small indicator bead on the end cap. For standard 5x20mm or 6.3x32mm electronic fuses, the "color" actually refers to the body material: clear glass indicates fast-acting/low-breaking-capacity, while opaque white ceramic indicates time-delay/high-breaking-capacity. Amperage is always stamped on the metal end caps.
The Master Cartridge Fuse Reference Tables
Below are the three distinct "color" systems you will encounter on the bench or in the field. Use the table that matches your physical fuse type.
1. UK BS 1362 Plug Fuses (Mains Voltage)
These are the fat, ceramic-bodied cartridge fuses found inside UK/Ireland 13A mains plugs. The body color is the primary amperage identifier.
| Body Color | Amperage | Typical Application | Standard |
|---|---|---|---|
| Red | 3A | Lighting, small electronics, shavers (up to ~700W) | BS 1362 |
| Brown | 13A | Heaters, kettles, power tools, large appliances (up to ~3120W) | BS 1362 |
| Black / Uncolored | 5A | Obsolete. Replace with 3A or 13A based on load. | Withdrawn |
2. IEC 60269 / DIN VDE 0636 Industrial Indicator Beads
For industrial cartridge fuses (like Neozed or Diazed types), the fuse body is usually ceramic and uncolored. The color code applies to the indicator bead or striker pin on the end cap, which pops out when the fuse blows.
| Indicator Color | Amperage | Indicator Color | Amperage |
|---|---|---|---|
| Pink | 2A | Blue | 20A |
| Brown | 4A | Yellow | 25A |
| Green | 6A | Black | 35A |
| Red | 10A | White | 50A |
| Grey | 16A | Orange | 63A |
| Red (Dark/Large) | 80A | Yellow (Dark/Large) | 100A |
3. Electronic 5x20mm & 6.3x32mm Body Material "Colors"
In low-voltage electronics, the body material color tells you the blow characteristic and interrupting rating, not the amperage. Amperage is laser-etched or stamped on the nickel-plated brass end caps.
| Body Color/Material | Characteristic | Breaking Capacity | Internal Element |
|---|---|---|---|
| Clear Glass | Fast-Acting (F) | Low (LBC) - typically 35A or 10x rated current | Thin silver/copper wire |
| Opaque White Ceramic | Time-Delay / Slow-Blow (T) | High (HBC) - typically 1500A at 250VAC | Thick copper with solder blob, packed in quartz sand |
Rows People Get Wrong (And How to Fix Them)
- The IEC Red/Yellow Trap: Notice in the IEC table that Red means 10A, but also 80A. Yellow means 25A, but also 100A. The differentiation is physical size and the fuse base gauge ring. If you are replacing a 10x38mm industrial cartridge, rely on the stamped text on the ceramic body, not just the bead color, to avoid a catastrophic mismatch.
- The "Clear Glass is Always Fast-Blow" Myth: While 95% of clear glass 5x20mm fuses are fast-acting, some manufacturers produce slow-blow glass fuses with a visible spring-and-solder element inside. Always look for the letter F (Fast) or T (Time-delay/Träge) stamped next to the amperage (e.g., "T3.15AL250V").
- AGC Automotive Cap Colors: Older 6.3x32mm AGC (Automotive Glass Cartridge) fuses sometimes featured colored metal end caps (e.g., red caps for 10A). This is an abandoned, non-standardized manufacturer quirk from the 1970s. Ignore cap color on AGC fuses; read the stamp.
Regional Standards: Which One Applies to You?
Your geographic location and the equipment's origin dictate which standard you must follow. According to the IEC Standards Catalog, international harmonization is improving, but legacy physical formats remain strictly regional.
- North America (NEC / UL 248-14): You will primarily encounter 6.3x32mm (1/4" x 1-1/4") glass/ceramic fuses in electronics and 10x38mm (13/32" x 1-1/2") midget fuses in industrial control panels. There is no body color code. Identification is purely textual (e.g., "10A 250V"). Look for UL or CSA markings on the end caps.
- Europe (IEC 60269 / EN 60269): Industrial panels use Diazed (D-type) or Neozed (DO-type) fuses with the indicator bead color codes listed above. Electronics use 5x20mm glass/ceramic. The Littelfuse Cartridge Fuse Guide is an excellent cross-reference for European metric sizes versus North American imperial sizes.
- United Kingdom & Ireland (BS 1362): Mains plugs strictly require the Red (3A) and Brown (13A) ceramic cartridge fuses. The UK Gov Plug Safety Regulations mandate that replacement fuses must carry the ASTA or BSI kite mark to ensure the ceramic body can withstand the arc energy of a 240V dead short.
Safe Interpretation When Markings Are Faded or Missing
On older equipment, the stamp on the metal end caps of a 5x20mm fuse can rub off, or the ceramic body of an industrial fuse can become scorched black. Never guess the amperage based on wire thickness alone. Follow this diagnostic protocol:
- Verify Continuity: Use a multimeter in continuity/resistance mode. A good fuse reads < 1 ohm. An open reading (OL) confirms it is blown and must be replaced.
- Check the Appliance Nameplate: Look for "Max Input Current" or "Fuse Rating" on the chassis. If the nameplate says "250W Max" at 120V, the steady-state draw is ~2.08A. A 3A or 4A slow-blow fuse is the correct engineering choice.
- Inspect the PCB Silkscreen: On circuit boards, the fuse holder is almost always labeled on the silkscreen (e.g., "F1: 2A 250V T").
- Examine the Blown Element: If it's a clear glass fuse, look at the failure mode. A thin, cleanly broken wire indicates normal aging or a minor surge (correct fuse size). A shattered glass tube with black soot and vaporized metal indicates a massive dead short, and the fuse was likely under-rated for the circuit's fault current (you need an HBC ceramic replacement).
Decision Path: Identifying and Replacing Your Fuse
Use this decision tree to terminate your troubleshooting and select the exact replacement part. Do not deviate from the voltage and breaking capacity ratings.
| Your Scenario / Fuse Type | Action Required | Concrete Part Pick (Order This) |
|---|---|---|
| UK Mains Plug: Appliance is < 700W (e.g., desk lamp, phone charger, radio). | Install 3A Red ceramic fuse. Ensure it has a BSI/ASTA mark. | Bussmann BBS-3 or generic BS1362 3A Red (Pack of 5) |
| UK Mains Plug: Appliance is > 700W or has a heating element/motor (e.g., kettle, drill). | Install 13A Brown ceramic fuse. | Bussmann BBS-13 or generic BS1362 13A Brown (Pack of 5) |
| PCB Electronics: Clear glass 5x20mm, text reads "F" (Fast). Used for sensitive IC protection. | Match stamped amperage exactly. Do not upsize. | Littelfuse 0218 Series (e.g., 0218002.MXP for 2A Fast-Acting) |
| PCB Electronics / Power Supply: White ceramic 5x20mm, text reads "T" (Time-Delay). Handles inrush current. | Match stamped amperage. Must be HBC (High Breaking Capacity). | Littelfuse 0215 Series or Bussmann S500 Series (e.g., S500-2-R for 2A Slow-Blow) |
| Industrial Panel: 10x38mm Ceramic with indicator bead. Bead color matches IEC chart. | Verify stamped text on body. Match voltage (e.g., 400VAC vs 500VAC) and gG/gL class. | Mersen ATDR Series or Bussmann 170M Series matching stamped amps |
By treating the cartridge fuse color code as a system of material properties and regional indicators rather than a simple rainbow chart, you ensure both the safety of the operator and the longevity of the equipment. Always default to the stamped text, verify the breaking capacity requirement, and source from authorized distributors to avoid counterfeit fuses that lack internal quartz sand.
