Reference
RV Fuse and Breaker Size Chart by Circuit Current
Researched from published standards and manufacturer specifications. Updated .
Quick answer
A fuse protects the wire, not the appliance, and it must never exceed the ampacity of the conductor it is on. NEC 210.20(A) sizes an overcurrent device at 125 percent of a continuous load, so a 30A continuous load needs at least 37.5A of capacity, rounding up to the next standard rating of 40A. On a large lithium bank, a Class T fuse is the safer main-fuse choice over an ANL, because LiFePO4 can deliver very high short circuit current that not every fuse type can safely interrupt.
A fuse or breaker exists to protect the wire it sits on, not the appliance downstream of it. If the fuse rating exceeds what the conductor can safely carry, the wire can overheat well before the fuse ever opens, which is why fuse size is a function of wire gauge and continuous load, not of what feels roomy for the appliance.
This chart gives the standard rating series, the size needed for a continuous load under the 125 percent rule, the largest fuse each wire gauge can safely carry, and the fuse body types used in 12V RV wiring so the right physical fuse, not just the right number, gets chosen.
What does a fuse actually protect?
A fuse or circuit breaker protects the wire between the power source and the load, not the appliance on the end of it. Its job is to open the circuit before the conductor overheats and becomes a fire risk, which means the fuse rating is chosen from the wire ampacity downward, never chosen to suit an appliance and then wired to match. An oversized fuse on an undersized wire lets a fault current flow long enough to overheat the wire before the fuse ever reacts, which defeats the entire purpose of having one.
Standard fuse and breaker ratings
Every fuse size referenced on this site comes from one published series: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350 and 400 amps. A required rating that falls between two of these, such as 37.5A, always rounds up to the next size on the list, never down, and never to a non-standard in-between value.
Fuse or breaker size for a continuous load
NEC 210.20(A) requires an overcurrent device sized at 125 percent of a continuous load, a load expected to run three hours or more, then rounded up to the next standard rating from the series above.
| Continuous load (A) | Required at 125% (A) | Standard fuse or breaker to use (A) |
|---|---|---|
| 5 | 6.3 | 15 |
| 10 | 12.5 | 15 |
| 15 | 18.8 | 20 |
| 20 | 25.0 | 25 |
| 25 | 31.3 | 35 |
| 30 | 37.5 | 40 |
| 40 | 50.0 | 50 |
| 50 | 62.5 | 70 |
| 75 | 93.8 | 100 |
| 100 | 125.0 | 125 |
| 125 | 156.3 | 175 |
| 150 | 187.5 | 200 |
| 175 | 218.8 | 225 |
| 200 | 250.0 | 250 |
| 250 | 312.5 | 350 |
| 300 | 375.0 | 400 |
Published standard Source: NEC 210.20(A), overcurrent device sized at 125 percent of a continuous load. This sizes the fuse to the load. It must still be checked against the max-fuse-per-conductor table below, since the smaller of the two numbers governs.
Maximum fuse size that still protects the conductor
This is the ceiling in the other direction: the largest standard fuse or breaker rating that does not exceed the wire's own ampacity under ABYC E-11. A fuse sized above this number no longer protects the conductor, no matter how the load-based table above worked out.
| AWG | ABYC E-11 ampacity (A) | Max standard fuse at or below ampacity (A) |
|---|---|---|
| 16 | 25 | 25 |
| 14 | 35 | 35 |
| 12 | 45 | 45 |
| 10 | 60 | 60 |
| 8 | 80 | 80 |
| 6 | 120 | 110 |
| 4 | 160 | 150 |
| 2 | 210 | 200 |
| 1 | 245 | 225 |
| 1/0 | 285 | 250 |
| 2/0 | 330 | 300 |
| 3/0 | 385 | 350 |
| 4/0 | 445 | 400 |
Published standard Source: ABYC E-11 ampacity paired with the NEC 240.6(A) standard fuse series; the fuse or breaker must never exceed the conductor ampacity. This is the ceiling for that wire gauge alone. A shorter or longer run can still need a smaller fuse to hold voltage drop, which the wire gauge chart on this site covers separately, and NEC 240.4(D) overrides this ceiling further down on 14, 12 and 10 AWG at 15A, 20A and 30A.
Where the fuse actually belongs in the circuit
A fuse protects the wire that comes after it, not the wire before it, which means it needs to sit as close to the power source as practical, ideally within a few inches of the battery terminal for a main disconnect. A long unprotected run between the battery and the first fuse is a length of wire with no overcurrent protection at all, which defeats the purpose of the fuse further down the circuit. This is exactly why MRBF fuses exist: mounting the fuse directly on the battery terminal shrinks that unprotected length to nearly zero, and it is why an ANL or Class T main fuse should be placed as close to the battery as the physical layout allows rather than wherever is most convenient to reach.
Fuse body types used in 12V RV wiring
Amperage rating is only half the fuse choice. The physical body type matters for where it mounts and, on a large lithium bank, for whether it can safely interrupt the current available.
| Type | Typical amperage range | Common use | Note |
|---|---|---|---|
| ATO / ATC blade | 1 to 40A | Low-current 12V circuits: lighting, pumps, fans | The small automotive-style blade fuse used in most RV distribution panels. |
| MIDI / AMI | 30 to 200A | Mid-size feeds: inverter input, DC-DC charger input | Bolt-down blade style, a smaller footprint than an ANL at the same rating. |
| ANL | 35 to 500A | Main battery disconnect and large bus feeds | Bolt-down body, the common choice for a lithium house bank main fuse. |
| MRBF | 30 to 300A | Mounted directly on a battery terminal | Shortest possible unprotected wire length between the battery post and the fuse. |
| Class T | 100 to 800A | Main fuse on a large lithium bank or a high-output inverter feed | Higher published interrupt rating than ANL in most lines, the safer choice where a large LiFePO4 bank can deliver very high short circuit current. Confirm the specific manufacturer interrupt rating in kA before buying. |
| Manual reset circuit breaker | 5 to 300A | Any circuit where replacing a blown fuse is inconvenient | Resettable, but check the trip curve; not every breaker trips as fast as a fuse on a dead short. |
Convention Source: Fuse body type ranges and typical use are drawn from manufacturer fuse holder specifications, not a single NEC table. Confirm the interrupt rating in kA on the specific manufacturer datasheet before choosing a fuse type for a large lithium bank main disconnect.
A large lithium bank can outrun an ordinary fuse's interrupt rating. LiFePO4 cells can deliver very high short circuit current, high enough that a fuse without a sufficient interrupt rating may not safely open under a true short. Check the interrupt rating in kA on the specific fuse against the bank's maximum fault current, and favor a Class T fuse on a large lithium main disconnect for that reason.
Fuses and holders to build the chart above
Buy the fuse rating the max-fuse table below actually allows for the wire already run, and mount it in a body rated for the fuse class, ANL, MRBF or Class T, not whatever holder happened to be on hand.
iRhapsody 200A ANL Fuse Holder Kit, 3 Pack
$13.99Matches the max-fuse figures this chart shows for 3/0 and 4/0 AWG main battery runs.
Best for: Fusing several circuits in one build.
Check price on Amazon
BOJACK 200A Inline ANL Fuse Holder with Fuse
$15.99Bolt-down inline body built for the ANL fuse class covered in the body-type table below.
Best for: Fusing an inverter feed at the battery.
Check price on Amazon
RECOIL ZAFH2-200 Inline ANL Fuse Holder
$13.99Smaller footprint holder for a main fuse mounted close to the battery terminal.
Best for: A tidy inline fuse on a heavy cable.
Check price on Amazon
RVMARINEPAT 12V 250A Busbar, 6 Studs
$26.99Gives multiple fused branch circuits a single, properly rated landing point off the main fuse.
Best for: A build with several circuits leaving the bank.
Check price on AmazonFrequently asked questions
- Does a fuse protect the appliance or the wire?
- The wire. A fuse or breaker is chosen based on the ampacity of the conductor it protects, so that it opens the circuit before the wire overheats. An appliance with its own internal protection does not change what fuse rating the wire itself needs; oversizing a fuse to avoid nuisance trips on an appliance defeats its actual purpose.
- What is the 125 percent continuous load rule?
- NEC 210.20(A) requires an overcurrent device rated at least 125 percent of a continuous load, defined as one expected to run three hours or more, then rounded up to the next standard fuse or breaker size. A 30A continuous load needs at least 37.5A of capacity, which rounds up to a 40A fuse or breaker on the standard rating series.
- Why does a large lithium bank need a Class T fuse instead of an ANL?
- LiFePO4 cells can deliver extremely high short circuit current compared to lead-acid, and not every fuse type has an interrupt rating high enough to safely open under that much fault current. Class T fuses generally publish a higher interrupt rating than ANL fuses in the same amperage class, which is why they are the more conservative main-fuse choice on a large lithium bank. Always confirm the specific manufacturer interrupt rating rather than assuming by fuse type alone.
- Can I use a larger fuse than my wire ampacity to stop nuisance blows?
- No. A fuse rated above the conductor's ampacity no longer protects that wire, since a fault current the wire cannot safely carry will flow long enough to overheat it before the oversized fuse opens. A nuisance-blow problem means the wire, the fuse rating, or the load itself needs to be re-evaluated, not that the fuse should be sized up past the wire.
- What is the difference between an ANL fuse and an MRBF fuse?
- Both are bolt-down fuse bodies used on 12V battery circuits, but an MRBF is designed to mount directly on the battery terminal itself, minimizing the length of unprotected wire between the post and the fuse. An ANL typically mounts inline a short distance away in a separate holder. Either can serve as a main disconnect fuse; MRBF simply shortens the unprotected run to nearly zero.
- Is a circuit breaker as safe as a fuse for a battery main disconnect?
- A manual reset circuit breaker can serve the same protective role as a fuse, but its trip curve should be checked against the wire and fault current it protects, since not every breaker opens as fast as a fuse does on a dead short. A breaker rated for the correct continuous current and with a documented trip curve suited to the application is a legitimate choice; one substituted without checking the trip speed is not automatically equivalent.
Two ceilings, use the smaller one. Size the fuse up from the continuous load using the 125 percent rule, check it against the maximum fuse the wire gauge can carry, and use whichever number is smaller. On a large lithium bank, also confirm the fuse body's interrupt rating in kA before treating the amperage number alone as sufficient.