Quick answer
Standard Fuse Sizes
Standard fuse ratings span 1 A through 6000 A. The highlighted values are fuse-specific ratings in the NEC 240.6(A) standard-rating sequence.
Important: a standard ampere rating is not, by itself, a complete fuse selection. Voltage rating, interrupting rating, fuse class, time-current behavior, conductor protection, equipment limits, and application-specific rules still apply.
Primary reference
Standard Fuse Size Chart
Find a standard nominal fuse rating and its equivalent load at a 125% reference factor. Use the quick lookup below when you need to convert a load first.
How to use: find the calculated requirement, then identify the first standard rating at or above it. The 125% column is a reverse-calculation reference only—not a universal allowable load.
No standard fuse ratings match the current search or filter.
| Copy | |||
|---|---|---|---|
| 1 AFuse-specific | 0.8 A | Fuse-specific | |
| 3 AFuse-specific | 2.4 A | Fuse-specific | |
| 6 AFuse-specific | 4.8 A | Fuse-specific | |
| 10 AFuse-specific | 8 A | Fuse-specific | |
| 15 A | 12 A | Standard sequence | |
| 20 A | 16 A | Standard sequence | |
| 25 A | 20 A | Standard sequence | |
| 30 A | 24 A | Standard sequence | |
| 35 A | 28 A | Standard sequence | |
| 40 A | 32 A | Standard sequence | |
| 45 A | 36 A | Standard sequence | |
| 50 A | 40 A | Standard sequence | |
| 60 A | 48 A | Standard sequence | |
| 70 A | 56 A | Standard sequence | |
| 80 A | 64 A | Standard sequence | |
| 90 A | 72 A | Standard sequence | |
| 100 A | 80 A | Standard sequence | |
| 110 A | 88 A | Standard sequence | |
| 125 A | 100 A | Standard sequence | |
| 150 A | 120 A | Standard sequence | |
| 175 A | 140 A | Standard sequence | |
| 200 A | 160 A | Standard sequence | |
| 225 A | 180 A | Standard sequence | |
| 250 A | 200 A | Standard sequence | |
| 300 A | 240 A | Standard sequence | |
| 350 A | 280 A | Standard sequence | |
| 400 A | 320 A | Standard sequence | |
| 450 A | 360 A | Standard sequence | |
| 500 A | 400 A | Standard sequence | |
| 600 A | 480 A | Standard sequence | |
| 601 AFuse-specific | 480.8 A | Fuse-specific | |
| 700 A | 560 A | Standard sequence | |
| 800 A | 640 A | Standard sequence | |
| 1000 A | 800 A | Standard sequence | |
| 1200 A | 960 A | Standard sequence | |
| 1600 A | 1280 A | Standard sequence | |
| 2000 A | 1600 A | Standard sequence | |
| 2500 A | 2000 A | Standard sequence | |
| 3000 A | 2400 A | Standard sequence | |
| 4000 A | 3200 A | Standard sequence | |
| 5000 A | 4000 A | Standard sequence | |
| 6000 A | 4800 A | Standard sequence |
125% load reference: nominal fuse rating ÷ 1.25. It is a mathematical lookup aid only. Do not treat it as a universal permissible load or conductor ampacity. Final overcurrent protection must comply with the protected conductor, equipment instructions, and applicable code.
Table tools
Quick general-load lookup
Quick Fuse Size Lookup
Convert a general load to amperes, apply the selected reference factor, and find the first standard fuse rating at or above the calculated requirement.
Important
This lookup identifies a standard ampere rating only. Before selecting a fuse, verify conductor protection, equipment instructions, voltage rating, interrupting rating, fuse class, time-current behavior, and all application-specific code requirements.
Conductor protection
Common Copper Wire & Fuse Reference
Small-conductor overcurrent limits are useful checkpoints, but conductor ampacity and permitted overcurrent protection depend on the actual installation.
| Copper wire | Common maximum OCPD reference | What to verify |
|---|---|---|
| 14 AWG | 15 A | Small-conductor rule and all listed exceptions. |
| 12 AWG | 20 A | Small-conductor rule and all listed exceptions. |
| 10 AWG | 30 A | Small-conductor rule and all listed exceptions. |
| 8 AWG | Application dependent | Allowable ampacity, terminal temperature, conductor material, adjustment/correction factors, equipment limits, and OCPD rules. |
| 6 AWG | Application dependent | Allowable ampacity, terminal temperature, conductor material, adjustment/correction factors, equipment limits, and OCPD rules. |
Do not size from gauge alone
The table is a checkpoint, not a universal wire-to-fuse conversion chart. Aluminum conductors, higher-temperature insulation, derating, terminals, cable assemblies, motors, HVAC equipment, and other special applications can require different treatment.
Selection beyond amperes
Common Fuse Classes
Two fuses with the same ampere rating are not automatically interchangeable. Class, voltage, interrupting rating, dimensions, rejection features, and time-current behavior matter.
| Fuse class | Typical range / role | Selection note |
|---|---|---|
| Class CC | Compact branch-circuit fuses, typically through 30 A | Available in time-delay and fast-acting families; verify the exact product. |
| Class J | Current-limiting branch-circuit fuses, commonly through 600 A | Compact footprint; both time-delay and fast-acting product families exist. |
| Class RK1 | Current-limiting Class R protection, commonly through 600 A | Time-delay and fast-acting families are available; Class R rejection features help prevent substitution with lower-performing fuses. |
| Class RK5 | Class R time-delay protection, commonly through 600 A | Often used where temporary inrush must be tolerated; verify product time-current data. |
| Class T | Compact fast-acting current-limiting protection | Useful where a small footprint and high interrupting capability are required; verify voltage and ampere range for the exact family. |
| Class L | High-current protection, commonly 601–6000 A | Used for large feeders and equipment; both time-delay and fast-acting product families exist. |
Key takeaways
What the Result Means
- Load current is converted from the entered current, real-power, or apparent-power value.
- Calculated minimum equals load current multiplied by the selected reference factor.
- First qualifying standard rating is the smallest listed nominal rating not below the calculated requirement.
- Final selection still depends on the protected conductor or equipment and the exact fuse family.
Why the Calculated Fuse Size May Still Be Wrong
A higher nominal rating can violate conductor or equipment limits even when it is the next standard value. Motor, transformer, HVAC, photovoltaic, semiconductor, and automotive circuits can use application-specific rules, nameplate instructions, and time-current requirements that override a general multiplier.
Fuse ampere rating is only one selection property. The fuse must also be appropriate for circuit voltage, AC or DC interruption, available fault current, response speed, ambient conditions, pulse or inrush energy, fuseholder rating, coordination, dimensions, and required listings or approvals.
Fuse Sizing Formulas
The quick lookup first converts the entered general load to amperes. It then multiplies that current by the selected reference factor and identifies the first standard nominal rating at or above the calculated requirement.
Current conversion
- DC or single-phase VA
- I = S ÷ V
- Three-phase VA
- I = S ÷ (√3 × VLL), where VLL is line-to-line voltage
- Single-phase watts
- I = P ÷ (V × PF)
- Three-phase watts
- I = P ÷ (√3 × VLL × PF), where VLL is line-to-line voltage
Variable definitions
- ICurrent in amperes
- PReal power in watts
- SApparent power in volt-amperes
- VDC, single-phase, or line-to-line voltage as selected
- PFPower factor as a decimal from greater than 0 through 1
Worked Fuse Sizing Examples
16 A continuous load
Assumption: a 125% reference factor is selected.
16 A × 1.25 = 20 A.
The first listed nominal rating is 20 A. Confirm that the conductor and equipment permit that rating.
5 kW, 240 V single-phase load
Assumption: PF = 1.00.
5,000 W ÷ 240 V = 20.83 A. At a 125% reference factor, the calculated requirement is 26.04 A.
The first listed nominal rating is 30 A, subject to all conductor, equipment, and application limits.
15 kVA, 480 V three-phase load
15,000 VA ÷ (√3 × 480 V) = 18.04 A.
At a 125% reference factor, the calculated requirement is 22.55 A, so the first listed rating is 25 A.
Transformer or equipment-specific rules may produce a different permitted protective-device rating.
18 A continuous-load reference
Assumption: a 125% reference factor is selected.
18 A × 1.25 = 22.5 A.
The first standard rating at or above 22.5 A is 25 A. Final protection still depends on the conductor, equipment, and application rules.
Fuse Selection Checklist
1. Confirm the protected item
- Branch-circuit conductor
- Equipment or component
- Motor, transformer, HVAC, PV, or electronic load
2. Verify electrical ratings
- Nominal ampere rating
- AC or DC voltage rating
- Interrupting rating above available fault current
3. Verify operating behavior
- Fast-acting or time-delay response
- Starting current, inrush, or pulse energy
- Ambient temperature and enclosure conditions
4. Verify installation constraints
- Fuse class and rejection features
- Fuseholder rating and dimensions
- Coordination, current limitation, and approvals
Fast-acting vs time-delay fuses
| Characteristic | Fast-acting | Time-delay |
|---|---|---|
| Typical behavior | Opens quickly during sustained overcurrent. | Allows defined temporary inrush before opening. |
| Common concern | Nuisance opening on startup or charging current. | Excess delay if applied where rapid component protection is required. |
| Selection basis | Use the equipment instructions and the exact manufacturer time-current data for the chosen fuse family. | |
Fuse amp rating vs voltage and interrupting rating
The fuse’s nominal current rating. It is only one part of selection.
The fuse must be rated for the circuit voltage and suitable for the AC or DC application.
The fuse must be capable of safely interrupting the available fault current under its applicable rating conditions.
Fast-acting and time-delay families respond differently to temporary inrush and sustained overcurrent.
Common fuse selection mistakes
- Replacing a nuisance-opening fuse with a larger rating without identifying the cause.
- Assuming an AC fuse is automatically suitable for the same DC voltage.
- Ignoring conductor ampacity, equipment maximum overcurrent protection, or terminal limits.
- Confusing nominal ampere rating with fuse class, interrupting rating, or response speed.
Engineering Basis and Sources
Scope: standard fuse ampere ratings, 125% load reference, general-load current conversion, first qualifying standard rating, small-conductor checkpoints, and fuse-selection checks.
This page uses an original calculation workflow and a compact summary of the standard nominal rating sequence in NEC 240.6, including the additional fuse-specific ratings. Supporting conductor and fuse-class sections are intentionally summarized and require verification against the locally adopted code edition and exact manufacturer product data.
- NFPA 70®, National Electrical Code®Supports overcurrent-protection principles, standard rating concepts, and application limitations. Use the locally adopted edition.
- ICC public NEC provisions excerpt — Section 240.6Provides a publicly viewable excerpt of the standard ampere rating sequence and the additional fuse-only ratings used by this reference.
- Littelfuse Fuseology Design GuideSupports the broader fuse-selection factors beyond nominal current, including voltage, ambient conditions, pulse energy, time-current behavior, and interrupting rating.
- Eaton Bussmann Fuseology HandbookSupports the fuse-class overview and the distinction among time-delay, fast-acting, current-limiting, and high-current fuse families.
Dataset and Review Details
- Publisher
- Turn2Engineering
- Page type
- Educational calculator and transformed reference
- Canonical units
- Amperes, volts, watts
- Calculation method
- Power-to-current conversion, selected reference factor, first qualifying listed rating
- Known exclusions
- Manufacturer product tables, time-current curves, product availability, and project approval
- Rights status
- Original calculations and standards summary; CSV export disabled
Fuse Size Chart FAQs
The standard ampere-rating sequence shown on this page runs from 1 A through 6000 A. Fuse-specific standard ratings include 1, 3, 6, 10, and 601 A in addition to the common fuse / inverse-time breaker sequence.
Using a simplified 125% reference factor gives 20 A, so 20 A is the first standard rating at or above the calculated requirement. The conductor, equipment, voltage, interrupting rating, fuse class, and application rules must still permit it.
For the common small-conductor rule, 14 AWG copper is generally protected at no more than 15 A unless a specific permitted exception applies. Always verify the actual conductor, equipment, and code conditions.
For the common small-conductor rule, 12 AWG copper is generally protected at no more than 20 A unless a specific permitted exception applies. Final sizing depends on the actual installation.
For the common small-conductor rule, 10 AWG copper is generally protected at no more than 30 A unless a specific permitted exception applies. Do not extend this simple relationship to larger conductors without checking ampacity and overcurrent-protection rules.
No. The next standard rating can exceed a conductor or equipment limit, and application-specific rules may prohibit upward selection. Confirm the governing limit before choosing a larger fuse.
The 125% column is a reference calculation: fuse rating divided by 1.25. It is not a universal permissible load. When the quick lookup uses a 125% factor, it multiplies the entered load by 1.25 and then finds the first standard rating at or above that result.
Not automatically. A fuse must have an appropriate voltage and interrupting rating for the circuit and must be specifically suitable for the AC or DC application.
Fast-acting fuses respond quickly to sustained overcurrent, while time-delay fuses tolerate a specified temporary inrush. Use the equipment instructions and exact manufacturer time-current data for the selected fuse family.
Motor circuits use application-specific short-circuit and ground-fault protection rules and must be coordinated with overload protection and starting current. Use a dedicated motor/fuse sizing workflow rather than the general-load reference alone.
Interrupting rating is the maximum fault current a fuse is approved to interrupt safely under its rating conditions. It is separate from the normal ampere rating and must be adequate for the available fault current.
Use the Chart as a Starting Point
Start with the standard fuse-size chart, use the quick lookup only when you need to convert a general load into a reference requirement, and treat the first qualifying standard rating as a lookup result—not final approval. Before installation, verify conductor, equipment, voltage, interrupting, time-current, environmental, and code constraints for the actual circuit.