Fuse Size Calculator for 12V, 24V, 48V DC
Enter watts or amps, get the correct fuse rating, fuse type, and placement advice for any DC circuit. Built for RVs, boats, campers, and off-grid solar systems.
Fuse Size Calculator
= 60W
= 16.4 ft (one way, round-trip calculated automatically)
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Fuse Size
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Download Cable for iOSMaximum Fuse Size by Wire Gauge (12V DC)
The fuse rating must never exceed the wire ampacity. This table shows the maximum fuse size for each common wire gauge, plus the recommended fuse type and typical loads on that circuit.
| Wire Gauge | Max Fuse | Fuse Type | Common Loads |
|---|---|---|---|
| 18 AWG / 0.75mm² | 7A | Blade (ATC) | LED strips, sensors, low-power electronics |
| 16 AWG / 1.0mm² | 10A | Blade (ATC) | Interior lights, small fans, USB outlets |
| 14 AWG / 1.5mm² | 15A | Blade (ATC) | Lighting circuits, vent fans, small 12V outlets |
| 12 AWG / 4.0mm² | 25A | Blade (ATC) | Water pumps, fridges, heater fans, 12V sockets |
| 10 AWG / 6.0mm² | 35A | MAXI Blade | Compressor fridges, large fans, small inverters |
| 8 AWG / 10.0mm² | 50A | MAXI Blade | Sub-panels, DC-DC chargers, 500W inverters |
| 6 AWG / 16.0mm² | 65A | ANL | 800W inverters, shore power chargers |
| 4 AWG / 25.0mm² | 85A | ANL | 1000W inverters, battery interconnects |
| 2 AWG / 35.0mm² | 110A | ANL | 1500W inverters, large battery banks |
| 1/0 AWG / 50.0mm² | 135A | Class T | Main battery fuse, 2000W inverters (lithium) |
| 2/0 AWG / 120.0mm² | 235A | Class T | 3000W inverters, bus bars, lithium systems |
| 3/0 AWG / 150.0mm² | 285A | Class T | Bow thrusters, windlasses, high-power marine |
| 4/0 AWG / 185.0mm² | 330A | Class T | 5000W inverters, large marine battery banks |
Fuse Type Selection Guide
The right fuse type depends on current rating, battery chemistry, and available fault current. Use this guide to pick the correct physical fuse for each circuit.
Blade Fuses (ATC/ATO) -- 0 to 30A
Standard automotive blade fuses. Cheap, color-coded, available everywhere. Use for branch circuits: lights, outlets, fans, small pumps. Minimum fault-interrupt rating (1000A) is enough for lead-acid batteries in small systems.
MAXI Blade Fuses -- 30 to 60A
Larger physical blade fuses for higher current. Use for fridges, DC-DC chargers, sub-panels, and small inverters. Same mounting style as regular blade fuses, just sized up.
ANL Fuses -- 60 to 300A
Bolt-down strip fuses mounted in dedicated fuse holders. Standard choice for inverter feeds, battery mains, and high-current DC loads on lead-acid systems. AIC rating around 2,700A -- adequate for lead-acid batteries but not lithium.
Class T Fuses -- 30 to 400A
Fast-acting, high fault-interrupt fuses required for lithium battery banks. AIC rating 20,000A DC -- high enough to safely clear a shorted LiFePO4 battery. Use at the main battery fuse position in any lithium system.
MIDI/AMI Fuses -- 30 to 200A
Compact bolt-down fuses used in modern European marine and automotive systems. Smaller footprint than ANL, common in Victron and Bluesea fuse holders.
Mega Fuses -- 60 to 500A
Bolt-down fuses similar in form factor to ANL but with higher current ratings. Common in heavy vehicles and marine applications where very high currents are expected.
Frequently Asked Questions
What size fuse do I need for my 12V circuit?
Enter your load in watts or amps in the calculator above, and it returns the recommended fuse rating and type immediately. The rule is: take the continuous load current, multiply by 1.25, then round up to the next standard fuse size. A 60W load at 12V draws 5A, so a 7.5A fuse is the minimum. The fuse rating must never exceed the wire ampacity.
What size fuse for a 2000W inverter on 12V?
A 2000W inverter at 12V can draw up to 167A continuously (2000W / 12V), with surge peaks much higher. Apply the 125% rule: 167A × 1.25 = 209A, so a 250A ANL or Class T fuse is standard. Use 2/0 AWG or 35mm² wire minimum, and keep the cable run as short as possible. The calculator above sizes both the fuse and wire for your specific inverter and cable length.
What size fuse for a 1000W inverter on 12V?
A 1000W inverter at 12V draws around 83A continuously. Applying the 125% safety margin (104A) and rounding up, a 125A or 150A ANL fuse is typical. Use 4 AWG (25mm²) battery cable minimum. The calculator will show exact values for your cable length.
What size fuse for 14 gauge wire 12V?
14 AWG (1.5mm²) wire is rated for 15A continuous. The fuse must be at or below 15A -- typically a 10A or 15A blade fuse depending on your actual load. Never install a fuse larger than the wire can safely carry, because the fuse protects the wire, not the device.
What size fuse for 12 gauge wire 12V?
12 AWG (4.0mm²) wire is rated for 25A continuous. A 20A or 25A blade fuse is appropriate. Choose the fuse based on your actual load current (125% of continuous load, rounded up), making sure it does not exceed the 25A wire ampacity.
What size fuse for 10 gauge wire 12V?
10 AWG (6.0mm²) wire is rated for 35A continuous. A 30A or 35A MAXI blade fuse is common. Always size the fuse to match the load, but never above the wire rating -- 35A is the absolute maximum.
What size fuse for 8 gauge wire 12V?
8 AWG (10mm²) wire handles 50A continuous. MAXI blade fuses up to 50A or an ANL fuse holder work here. Common uses: sub-panels, DC-DC chargers, medium-size shore power chargers.
What size fuse for a 12V battery?
The main battery fuse protects the entire positive feed from the battery and must be rated for the total continuous current draw of all circuits combined. For a typical camper or boat with 100-200A total system load, a 150A, 200A, or 250A ANL or Class T fuse is standard. Every individual branch circuit leaving the fuse box also needs its own smaller fuse matched to the circuit wire.
What type of fuse should I use?
Blade fuses (ATC/ATO) cover 0-30A and are the most common for accessory circuits. MAXI blade fuses handle 30-60A for fridges, chargers, and sub-panels. ANL bolt-down fuses cover 60-300A for battery mains and inverter feeds. Class T fuses are required for lithium battery banks and high-power inverters because they have the fault-interrupt rating to safely clear a shorted lithium battery (AIC rating up to 20,000A).
How far from the battery should a fuse be placed?
As close as physically possible, ideally within 18cm (7 inches) of the battery positive terminal. The wire between the battery and the fuse is unprotected -- if it shorts to chassis, there is nothing to prevent a fire. This is the single most important fuse placement rule in any DC electrical system.
Does the fuse protect the load or the wire?
The fuse protects the wire, not the load. A fuse blows when current exceeds the wire ampacity, preventing the wire from overheating and starting a fire. Loads like inverters and appliances have their own internal protection. Size your fuse based on the wire it protects, capped at 125% of the continuous load current.
Can I use a circuit breaker instead of a fuse?
Yes, DC-rated circuit breakers are interchangeable with fuses for most applications and have the advantage of being resettable. Make sure the breaker is DC-rated (AC-only breakers will not safely interrupt a DC fault) and has the correct AIC rating for lithium battery systems. ANL and Class T fuses are still preferred at the main battery because of their high fault-interrupt capacity.
What happens if my fuse is too large?
A fuse rated higher than the wire ampacity will not blow before the wire overheats, defeating its purpose. This is the most common cause of electrical fires in DC systems. If the calculator returns a fuse size that seems high, check that your wire gauge actually supports that current -- the calculator flags any mismatch between load, wire, and fuse.
What happens if my fuse is too small?
A fuse smaller than the continuous load current will blow under normal operation (nuisance tripping). This often indicates that either the load was underestimated or the fuse was sized too conservatively. The correct size is 125% of continuous load, rounded up to the next standard rating.
How to Size a Fuse Correctly
Fuse sizing is the single most important safety step in any DC electrical installation. An incorrectly sized fuse either blows under normal load (annoying but safe) or fails to blow during a fault (dangerous, fire risk). The process is the same whether you are wiring a van, a boat, or an off-grid solar shed.
Step 1: Determine the Continuous Load Current
Continuous means the current the circuit will draw in normal operation -- not the peak, not the inrush, just the steady-state amp draw. For appliances rated in watts, divide watts by system voltage: a 600W device on 12V draws 50A. For inverters, use the maximum continuous output, not the peak surge rating.
Step 2: Apply the 125% Safety Margin
Multiply continuous current by 1.25. This 25% headroom covers inrush events, ambient temperature effects, and normal variation. Many electrical codes (ABYC, NEC) enforce this margin. A 50A continuous load becomes 62.5A sizing target.
Step 3: Round Up to the Next Standard Fuse
Fuses only come in standard ratings: 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100, 125, 150, 175, 200, 250, 300, 400A. You must round up -- not down -- to the next available size. 62.5A becomes 80A.
Step 4: Check Against Wire Ampacity
The fuse rating must never exceed the wire ampacity. If your calculated fuse size is larger than the wire can safely carry, you must upgrade the wire. Fuse first, wire second is the wrong order. Wire first, fuse matched to wire is the correct order.
Step 5: Pick the Correct Fuse Type
Blade fuses for small circuits, MAXI blade for medium, ANL for high-current lead-acid systems, Class T for lithium battery mains. The physical fuse type matters as much as the rating -- the wrong type can fail to clear a fault even at the right current.
Fuse Placement Rules That Save Lives
The fuse protects the wire from the short-circuit point backwards to the battery. Any unfused wire between the battery positive terminal and the fuse is unprotected. That is why every DC installation manual specifies: fuse within 18cm (7 inches) of the battery, protected with a dedicated fuse holder, accessible for inspection but not exposed to weather or impact.
Lithium vs Lead-Acid: Why Class T Matters
A shorted lithium battery can deliver 15,000-20,000A of fault current for the fraction of a second before the cells fail. ANL fuses are only rated to safely interrupt 2,700A. Use Class T fuses at the battery main on any lithium system -- this is an ABYC requirement and a non-negotiable safety rule.
Related Resources
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