The standard automotive blade fuse ecosystem is governed by three primary specifications: SAE J1284 for standard and large blade fuses, SAE J2077 for miniature and low-profile variants, and ISO 8820 for general road vehicle fuses. If you are replacing a blown fuse or designing an aftermarket wiring harness, the physical footprint and amperage limits are strictly defined by these standards. Below is the master reference chart for identifying and sizing these components.
The Master Automotive Fuse Type Chart
How to read this table: The 'Dimensions' column lists Length x Width x Height in millimeters, which dictates the physical slot compatibility on your fuse panel. The 'Max Voltage' column indicates the maximum safe DC operating voltage; while most standard fuses are rated for 32V DC, newer 48V mild-hybrid systems require specific 58V or 42V rated variants. The 'Amp Range' shows the available factory ratings, and the 'Standard Color (Max)' highlights the industry-standard color code for the highest common amperage in that physical size. Always verify the temperature column in your specific datasheet, as base ampacity is rated at a 20°C to 25°C ambient baseline.
| Fuse Type | Standard | Dimensions (LxWxH mm) | Max Voltage | Amp Range | Standard Color (Max Amp) |
|---|---|---|---|---|---|
| Micro2 | SAE J2077 | 15.3 x 9.1 x 8.3 | 32V DC | 5A - 30A | Green (30A) |
| Low-Profile Mini | SAE J2077 | 10.9 x 3.8 x 8.3 | 32V DC | 2A - 30A | Green (30A) |
| MINI | SAE J2077 | 10.9 x 3.6 x 15.3 | 32V DC | 2A - 30A | Green (30A) |
| ATO / ATC | SAE J1284 | 19.1 x 5.1 x 18.5 | 32V DC | 1A - 40A | Aqua (40A) |
| MAXI | SAE J1284 | 29.2 x 8.9 x 34.3 | 32V DC | 20A - 120A | Purple (120A) |
Bookmark Quick-Jump: The Most Queried Sizes
- ATO/ATC (Standard Blade): The most common fuse in vehicles built between 1980 and 2010. If you are pulling a 20A yellow or 15A blue fuse from a standard interior panel, it is an ATO. Note that ATO (open top) and ATC (closed top) are physically interchangeable, but ATC is preferred in under-hood environments to prevent moisture ingress.
- MINI vs. Low-Profile Mini: These are frequently confused. The standard MINI is 15.3mm tall, while the Low-Profile Mini is only 8.3mm tall. A standard MINI will not fit into a low-profile slot, but a low-profile MINI can sometimes be forced into a standard MINI slot, resulting in a loose connection and potential arcing. Always match the height exactly.
Temperature Derating and Continuous Load Rules
A common mistake in aftermarket automotive wiring—such as installing a 12V fridge in a camper van or an inverter for a work truck—is sizing the fuse exactly to the continuous load. The amp ratings in the chart above assume an ambient temperature of roughly 25°C (77°F). Under-hood environments regularly exceed 85°C (185°F), and even interior cabin panels can reach 50°C in summer sun.
When selecting the correct column for your installation, look at the Time-Current Characteristic rather than just the nominal amp rating. If your installation is in a high-heat engine bay, you must either step up one fuse size (while proportionally increasing the wire AWG to maintain NEC-style ampacity protection) or use a high-temperature rated fuse specifically designed for 125°C under-hood environments.
High-Amp and Cartridge Fuse Reference
For main power distribution, alternator protection, and high-draw aftermarket accessories (like winches or heavy-duty inverters), blade fuses are insufficient. Cartridge and bolt-down fuses handle higher currents and offer better short-circuit interrupting ratings.
| Fuse Type | Form Factor | Max Voltage | Amp Range | Typical Application |
|---|---|---|---|---|
| JCase (Standard) | Female blade cartridge | 32V DC | 20A - 60A | ABS modules, cooling fans |
| JCase (Low Profile) | Shortened cartridge | 32V DC | 20A - 60A | Modern high-density fuse panels |
| MIDI / AMI | Bolt-down strip | 32V DC | 30A - 70A | Alternator feeds, battery terminals |
| MEGA / AMG | Large bolt-down strip | 32V DC | 100A - 500A | Main battery disconnects, winches |
When sourcing automotive fuses from major distributors, always verify whether you need a MIDI (older, slightly wider footprint) or an AMI (newer, slightly narrower footprint). While they often share bolt-hole spacing, the physical housing clearance in modern European vehicles strictly requires the AMI profile.
What This Chart Cannot Tell You
While physical dimensions and nominal amp ratings are standardized, a reference chart cannot replace a manufacturer datasheet for three critical parameters:
- Interrupting Capacity (Breaking Capacity): A 30A MAXI fuse is rated to carry 30A, but what happens during a dead short where current spikes to 2,000A? Standard blade fuses typically have an interrupting rating of 1,000A at 32V DC. If you are protecting a lithium battery bank capable of delivering 5,000A of short-circuit current, a standard blade fuse will violently rupture. You must use a fuse with a higher interrupting rating or pair it with a Class-T ceramic fuse.
- Time-Delay (Slow-Blow) Characteristics: The chart does not differentiate between fast-acting and time-delay fuses. Motors (like fuel pumps or radiator fans) draw 3x to 5x their running current for the first 500 milliseconds during startup. A time-delay fuse tolerates this inrush current without blowing, whereas a fast-acting semiconductor fuse of the same amperage would pop instantly. Always match the original equipment manufacturer's (OEM) time-delay specification.
- Voltage Drop Across the Fuse: Every fuse is a resistor. A 10A MINI fuse might have a voltage drop of 150mV at full load, while a 40A ATO might drop 50mV. In precision 5V or 3.3V sensor circuits routed through a fuse block, this voltage drop can cause microcontroller brownouts. For low-voltage logic circuits, use dedicated PCB-mounted fuses rather than routing through a standard automotive fuse panel.
For exact time-current curves and millivolt drop specifications, always consult the manufacturer's technical catalog for the specific part number you are installing. Never substitute a higher-amp fuse to solve a nuisance-blowing issue without first verifying that the wire gauge can handle the increased continuous current and that the fault is not caused by a degraded connection or failing motor.
