Fuse Size Calculator
Calculate a standard fuse size from load current or power, or estimate a motor branch-circuit fuse from full-load current and fuse type.
Calculator is for informational purposes only and does not establish code compliance or equipment approval. Terms and Conditions
General-load mode applies the selected load-duration factor, then selects the next standard fuse rating; motor mode uses NEC Table 430.52(C)(1) percentage limits.
Choose the fuse sizing method
Select the application and the way your electrical load is known.
Enter the known values
Required values stay visible. Optional safety checks are available under Advanced Options.
Fuse Size Result
The selected standard fuse is shown separately from the exact calculated current requirement.
Result details
- Calculated requirement—
Show calculation steps Review current conversion, sizing factor, standard fuse selection, assumptions, and checks
- Enter valid values to see the complete calculation.
Fuse Protection Path
See the source, selected fuse, optional conductor check, and load relationship in one protection path.
Electrical source to fuse to conductor to load diagram
The diagram updates to show circuit type and voltage, the calculated fuse rating, optional conductor ampacity status, and load current.
Fuse sizing does not replace conductor, equipment, voltage, interrupting-rating, or manufacturer checks.
Method, Sources, and Assumptions
Calculation basis, standard-rating reference, motor percentage limits, fuse selection limits, and final verification requirements.
General mode is a simplified current-sizing estimate using the selected load-duration factor and standard fuse ratings. Motor mode uses NEC Table 430.52(C)(1) percentage limits. Neither mode certifies code compliance.
- The initial 18 A continuous-load example is illustrative and is not a universal design recommendation.
- Final fuse selection must verify adopted code, conductor protection, equipment instructions, voltage rating, AC/DC suitability, available fault current, interrupting rating, and time-current behavior.
Calculator guide
How to Calculate Fuse Size
The Fuse Size Calculator above estimates a standard fuse ampere rating from load current or electrical input power, or a table-based motor branch-circuit fuse candidate from motor full-load current and fuse type. For a general load, the calculator determines current, applies the selected continuous or non-continuous load treatment, and maps the resulting sizing current to a supported standard fuse rating.
The displayed ampere rating is a candidate, not complete fuse approval. Before installation, verify conductor and equipment limits, the actual fuse voltage and AC/DC ratings, available fault current versus interrupting rating, fuse class or family, holder compatibility, and time-current behavior for the application.
- Best for
- General-load fuse sizing and preliminary motor branch-circuit fuse checks
- Main output
- Standard fuse size candidate in amperes
- Critical check
- The fuse must be suitable for the conductor, equipment, voltage, and available fault current
Fuse Size from Amps, Watts, and Voltage
The calculator changes the required inputs with the selected application. General-load mode accepts current directly or converts power to current; motor mode uses motor full-load current and a fuse-type percentage. Advanced fields add numeric checks for conductor ampacity, an existing fuse, fuse voltage rating, available fault current, and interrupting rating.
- Application
- Choose General load for the simplified load-duration method or Motor branch circuit for the NEC Table 430.52(C)(1) percentage method implemented by the calculator.
- Load Current
- Normal operating current in amperes for general-load sizing. Do not substitute a brief startup or inrush current for normal load current.
- Load Power
- Real electrical input power at the point being fused, in watts or kilowatts. When power is entered, the calculator converts it to current using circuit voltage and, for AC real-power inputs, power factor. If you only know equipment output power, account for efficiency or use the manufacturer’s input-current rating instead.
- Circuit Type and Voltage
- DC, single-phase AC, or three-phase AC. Three-phase power conversion uses line-to-line voltage. Voltage also supports the optional fuse voltage-rating check.
- Power Factor
- A decimal from 0 to 1 used when AC real power in watts or kW is converted to current. Use measured or manufacturer data when available rather than assuming unity power factor.
- Load Duration
- General-load mode applies 100% for the calculator’s non-continuous setting or 125% for the continuous setting labeled as 3 hours or more.
- Motor Full-Load Current
- Current used by the motor branch-circuit method. Where NEC Article 430 requires table full-load current, use the applicable NEC motor table value rather than automatically using nameplate amperes.
- Motor Fuse Type
- The supported motor calculation distinguishes dual-element time-delay fuses from the nontime-delay/time-delay Class CC percentage basis. The choice changes the maximum percentage used for many AC motors.
- Conductor Allowable Ampacity
- An optional numeric comparison in general-load mode. Enter ampacity only after the conductor’s applicable temperature, terminal, adjustment, correction, and installation conditions have been addressed.
- Available Fault Current and Interrupting Rating
- Optional values used together. The entered fuse interrupting rating must be at least the available fault current at the fuse location for the numeric check to pass.
- Recommended Standard Fuse Size
- The general-load result is the next rating in the calculator’s NEC 240.6 standard-fuse list at or above the calculated sizing current. It is a candidate, not automatic permission to use that device.
- Table-Based Fuse Candidate
- The motor result applies the selected NEC motor percentage to full-load current and then maps the result to the supported standard rating. It addresses branch-circuit short-circuit and ground-fault protection, not motor overload protection.
Fuse Size Formula and Calculation Method
There is no universal formula that says every fuse should equal load current multiplied by 1.25. The calculator uses different relationships for general loads, power-to-current conversion, and motor branch-circuit protection because those tasks have different electrical and code considerations.
General-load sizing current
Plain language: multiply the calculated load current by the selected load-duration factor, then compare the result with the supported standard fuse ratings.
In this calculator, \(F_d=1.00\) for the non-continuous setting and \(F_d=1.25\) for the continuous setting. The 125% option is an application-specific sizing assumption, not a universal fuse safety factor.
Mixed continuous and non-continuous loads
Plain language: add 125% of the continuous portion to 100% of the non-continuous portion.
The current calculator interface classifies one general load at a time as continuous or non-continuous. For a mixed-load circuit, calculate the two portions separately with this relationship and then complete the applicable conductor, equipment, and code checks.
Power-to-current conversion
For DC, divide real power by voltage. For single-phase AC, divide real power by voltage and power factor. For balanced three-phase AC, divide real power by the square root of three, line-to-line voltage, and power factor.
Motor branch-circuit fuse percentage
Plain language: multiply the applicable motor full-load current by the percentage associated with the motor and fuse type, then apply the motor rule for a standard fuse rating when the percentage result does not equal a standard rating.
The calculator does not automatically apply the larger heavy-start allowances available under specific motor-starting conditions. It reports the table-based candidate first.
- \(I_{f,\mathrm{req} }\)
- Required fuse sizing current Calculated current basis before selecting a standard fuse rating in general-load mode.
- \(F_d\)
- Load-duration factor Factor selected by the calculator’s continuous or non-continuous load setting.
- \(I_{\mathrm{load} }\)
- Load current Normal current entered directly or derived from electrical power.
- \(P\)
- Real power Electrical power used to derive current when the load is entered in watts or kilowatts.
- \(V\)
- Circuit voltage Voltage used in DC or single-phase power conversion.
- \(V_{LL}\)
- Line-to-line voltage Voltage used in the balanced three-phase real-power relationship.
- \(PF\)
- Power factor Ratio used when real AC power is converted to current.
- \(I_{f,\max}\)
- Motor fuse percentage value Table-based motor branch-circuit short-circuit and ground-fault fuse value before standard-size mapping.
- \(K_m\)
- Motor fuse multiplier Percentage from the supported NEC Table 430.52(C)(1) motor/fuse combination.
- \(I_{\mathrm{FLC} }\)
- Motor full-load current Applicable motor full-load current used for branch-circuit short-circuit and ground-fault protection sizing.
Fuse Size Example: 18 A Continuous Load
The calculator’s initial example uses an 18 A general load with the continuous-load setting. This is a useful example because the exact sizing current falls between two standard fuse ratings, so the difference between the calculated requirement and the nominal fuse candidate is visible.
Substitute the values
The exact calculated sizing current is 22.5 A. The next rating in the calculator’s standard-fuse list is 25 A.
Result
25 A standard fuse candidate
The 25 A result is a nominal selection produced from a 22.5 A requirement. It does not by itself prove that a 25 A fuse is allowed for the conductor or equipment.
How to Read the Fuse Size Result
Treat the displayed fuse size as a candidate generated by the selected calculation path. The useful engineering distinction is between the exact calculated current and the standard ampere rating that the calculator reports after that calculation.
Requirement versus rating
If the exact requirement is 22.5 A and the displayed fuse is 25 A, 22.5 A is the calculated current basis; 25 A is the nominal standard rating selected by the tool. Keep those two values separate when checking conductor and equipment limits.
Power-based sensitivity
With power, circuit type, and power factor held constant, current varies inversely with voltage. A 10% increase in voltage reduces the calculated current by about 9.1%, because \(I\propto1/V\). With voltage held constant, current changes directly with power.
Fast sanity check
A fuse candidate that is below the calculated sizing current is immediately suspect for the selected general-load method. A result several times the normal load current also deserves a unit, mode, and application check before selection.
Fuse Size vs Wire Size and Actual Fuse Selection
A fuse’s ampere rating answers only one selection question. A real installation also depends on conductor protection, equipment limits, circuit voltage, AC or DC application, available fault current, interrupting rating, and the fuse’s time-current characteristics.
Calculated requirement
This is the current produced by the selected sizing method before choosing a nominal device. For the default example, the requirement is 22.5 A.
Selected standard rating
This is the standard ampere rating the calculator maps to the requirement. Upward movement to a standard fuse value is not permission to exceed a conductor, equipment, or application-specific maximum.
Check the conductor, not just the load
NEC overcurrent protection is tied to conductor ampacity, with specific rules and exceptions. Eaton’s protective-device handbook summarizes NEC 240.4 by stating that conductors generally must be protected in accordance with their ampacities and explains the conditional next-higher-standard-rating provision in 240.4(B). Therefore, a fuse that is large enough for the load can still be too large for the conductor. Eaton Bussmann Selecting Protective Devices Handbook
The calculator’s optional Conductor Allowable Ampacity field is deliberately a basic numeric comparison. It does not derive ampacity from AWG size, conductor material, insulation temperature, terminal temperature, ambient correction, number of current-carrying conductors, or installation method.
When equipment provides a maximum fuse size, MOCP, or other manufacturer overcurrent limit, that value is an independent ceiling. A calculated standard fuse candidate does not override the equipment marking or instructions. The calculator does not currently accept a dedicated equipment-maximum-fuse input, so perform that comparison separately.
Check the equipment maximum fuse rating
Source and scope: Eaton Bussmann Selecting Protective Devices Handbook, summarizing NEC 240.4(D). Verify the exact circuit type and any permitted exception before applying these values.
| Copper conductor | Common maximum OCPD |
|---|---|
| 14 AWG | 15 A |
| 12 AWG | 20 A |
| 10 AWG | 30 A |
For common NEC applications, the small-conductor rules in 240.4(D) place specific overcurrent-protection limits on 14 AWG, 12 AWG, and 10 AWG copper conductors, subject to the listed exceptions. These limits are not a universal automotive, marine, RV, or equipment-wiring chart.
Common small-conductor limits
Understand the next-standard-size issue
Two ideas are easy to confuse. First, a load calculation may land between standard device ratings. Second, NEC 240.4(B) contains a specific next-higher-standard-rating allowance for conductor protection when its conditions are met. Do not assume that the mere existence of a larger standard fuse means 240.4(B) permits it for a particular conductor or circuit.
Verify fuse voltage rating and AC/DC suitability
Littelfuse defines fuse voltage rating as the maximum AC or DC voltage at which the fuse is designed to operate and states that the fuse voltage rating must equal or exceed circuit voltage. It also notes that a fuse used in a DC circuit must be specifically rated for DC use. Littelfuse POWR-GARD Technical Application Guide
A 250 V ampere rating label does not mean every 250 V fuse has identical AC and DC application capability. Use the actual fuse data sheet or listing for the circuit type.
Verify interrupting rating against available fault current
A fuse must be capable of interrupting the prospective fault current at its location. Compare the fuse’s published interrupting rating for the applicable voltage and AC/DC condition with the available fault current at the fuse line terminals. Littelfuse states that the interrupting rating should equal or exceed the available fault current. The calculator’s advanced check compares those two entered values directly:
For example, a 10 kA interrupting rating is not adequate where the available fault current is 18 kA, even if the fuse’s normal ampere rating is otherwise correct. Use the Fault Current Calculator for a simplified fault-current estimate when appropriate, then verify the study basis and equipment ratings.
Motors need a different protection path
Motor branch-circuit fuses are not sized by treating motor running current as an ordinary continuous load. NEC Table 430.52(C)(1) establishes percentage limits for motor branch-circuit short-circuit and ground-fault protective devices. Eaton’s 2023 NEC update shows 175% for dual-element time-delay fuses and 300% for nontime-delay fuses for many common AC motor categories, with 150% values for wound-rotor and constant-voltage DC motors in the fuse columns. Eaton Bussmann 2023 NEC fuse and motor protection update
For a 28 A applicable motor full-load current, the supported standard-AC/time-delay path gives \(28\times1.75=49\,A\), which maps to a 50 A standard fuse candidate. With the nontime-delay basis, \(28\times3.00=84\,A\), which maps to 90 A. Those larger values address motor branch-circuit short-circuit and ground-fault protection and starting behavior; they are not motor overload settings.
Time-delay behavior can matter more than simply increasing amps
Motors, transformers, capacitive inputs, and some power-electronic loads can draw high short-duration current during startup or energization. Littelfuse’s fuse-selection guidance treats time-current behavior and pulse \(I^2t\) as separate selection considerations. If a correctly selected fuse opens during normal inrush, compare the load’s inrush profile with the actual fuse time-current curve and manufacturer data before changing the ampere rating.
12 V, 24 V, and 48 V DC Fuse Sizing
For DC loads, current is calculated from electrical input power and circuit voltage using \(I=P/V\). The same power draws more current as voltage decreases, which is why 12 V battery circuits can require much larger conductors and fuses than 24 V or 48 V systems.
Example: 240 W load on 24 V DC
If the calculator’s continuous general-load setting is used, the simplified sizing current becomes \(1.25(10)=12.5\,A\), which maps to a 15 A standard fuse candidate in the calculator.
Do not use one DC fuse chart for every application
NEC building wiring, automotive wiring, marine systems, RV systems, battery systems, solar equipment, and listed electronic equipment do not all use the same conductor-ampacity rules, fuse families, or installation standards. Use the calculator to establish the current relationship, then apply the rules and manufacturer requirements that govern the actual system.
Inverters and equipment efficiency
If a fuse is on the DC input of an inverter or other converter, do not enter AC output watts as though they were DC input watts without accounting for efficiency. A useful current relationship is \(I_{DC}=P_{out}/(V_{DC}\eta)\), but the manufacturer’s specified fuse and conductor requirements should control final selection.
Common Fuse Sizing Mistakes
Most bad fuse selections come from using the wrong calculation path or omitting a second required check, not from arithmetic. These are the errors most likely to change the result or make an apparently reasonable fuse unsuitable.
Multiplying every load by 1.25
The calculator uses 1.25 only when its continuous-load option is selected. Motors use a separate percentage method, and equipment-specific circuits can have their own overcurrent rules or nameplate limits.
Using watts divided by volts for every AC load
For real-power AC inputs, power factor changes current. Three-phase power also requires the \(\sqrt{3}\) relationship and line-to-line voltage. Using \(I=P/V\) indiscriminately can understate current.
Rounding up without checking the wire
The next standard fuse size can exceed the conductor’s allowable overcurrent protection. Verify the actual conductor ampacity and any applicable next-size provision instead of treating rounding as automatic approval.
Upsizing because a fuse opens at startup
Nuisance opening can result from inrush, an unsuitable time-current curve, incorrect fuse class, excessive ambient temperature, a loose/high-resistance connection, or a real equipment fault. Diagnose the cause before increasing the amp rating.
Using motor nameplate current for the wrong purpose
NEC motor branch-circuit short-circuit and ground-fault protection commonly uses full-load current determined under Article 430 rules, while motor overload protection has a different basis. Do not interchange those values without checking the applicable requirement.
Ignoring voltage or interrupting rating
A fuse can have the correct ampere rating and still be unsuitable because its voltage rating is too low, it is not rated for DC use, or its interrupting rating is below the available fault current.
Assuming every fuse family behaves the same
Two 30 A fuses can have different voltage ratings, interrupting ratings, dimensions, rejection features, agency listings, and time-current curves. Select the actual fuse family from its published data, not the amp number alone.
Forgetting the fuse holder
The holder or disconnect must also be compatible with the selected fuse class, ampere rating, voltage, environment, and applicable listing. A suitable fuse does not make an unsuitable holder acceptable.
Standard Fuse Sizes and Motor Fuse Sizing
The calculator uses the NEC 240.6 standard ampere-rating set when it maps a calculated value to a nominal fuse candidate. Motor mode also uses the supported fuse percentages from NEC Table 430.52(C)(1). These are reference values, not a substitute for the rest of the applicable code and equipment requirements.
| Load current | Load setting | Sizing current | Calculator candidate |
|---|---|---|---|
| 10 A | Non-continuous | 10 A | 10 A |
| 10 A | Continuous | 12.5 A | 15 A |
| 16 A | Continuous | 20 A | 20 A |
| 18 A | Continuous | 22.5 A | 25 A |
| 20 A | Continuous | 25 A | 25 A |
These rows show what the calculator’s simplified general-load method returns. They are calculator candidates only; final conductor, equipment, and application checks still apply.
Quick general-load examples
| Rating group | Standard fuse ratings (A) |
|---|---|
| 1–100 A | 1, 3, 6, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 |
| 110–600 A | 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600 |
| 601–6000 A | 601, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000 |
Source: Eaton Bussmann Selecting Protective Devices Handbook, summarizing NEC 240.6 standard fuse ratings. Actual product families may not be manufactured in every listed rating.
| Motor type | Nontime-delay / time-delay Class CC | Dual-element time-delay |
|---|---|---|
| Single-phase / supported standard AC motor | 300% of FLC | 175% of FLC |
| Wound-rotor motor | 150% of FLC | 150% of FLC |
| DC constant-voltage motor | 150% of FLC | 150% of FLC |
Source: Eaton Bussmann 2023 NEC code update for 430.52. The calculator does not automatically apply the larger motor-starting allowances that can be available when the table-based size is insufficient to start the motor.
When a Fuse Size Calculator Is Not Enough
This is a Tier 3 electrical selection calculator, so a mathematically valid result should be treated as a screening and sizing aid rather than a complete design or code-compliance determination.
General-load method is simplified
The calculator applies either a 100% or 125% duration factor to one general load and then selects a standard rating. It does not model every feeder, branch-circuit, multi-load, transformer, capacitor, photovoltaic, HVAC, appliance, or equipment-specific overcurrent rule.
Conductor ampacity is user-supplied
The calculator does not derive final conductor ampacity from material, AWG/kcmil size, insulation, termination temperature, ambient conditions, raceway fill, bundling, or number of current-carrying conductors.
Motor mode is branch-circuit protection only
The motor calculation addresses short-circuit and ground-fault protective-device sizing for the supported motor/fuse categories. It does not size motor overload relays or automatically determine an allowed heavy-start exception.
Fault current is not calculated internally
The interrupting-rating check only compares values you enter. It does not calculate utility contribution, transformer impedance, conductor impedance, motor contribution, asymmetry, or changes in available fault current over time.
Time-current coordination is not modeled
The calculator does not read a manufacturer’s time-current curve, calculate selectivity, verify current limitation, or evaluate melting and clearing \(I^2t\) for a specific fuse series.
Local adoption controls
NFPA publishes the NEC, but jurisdictions adopt and amend editions on different schedules. Final work must use the edition and amendments that actually apply to the installation.
Special circuits need additional rules
Do not rely on the simplified general-load result alone for photovoltaic source/output circuits, transformer protection, HVAC motor-compressor circuits, welders, capacitor circuits, tap conductors, multi-motor feeders, battery energy-storage systems, or listed equipment with specific maximum-fuse markings.
Sources and Calculation Basis
The calculator behavior was checked against its implemented general-load and motor calculation paths. The motor percentage values shown here use 2023 NEC supporting material; verify the NEC edition and amendments adopted by the authority having jurisdiction before final design or installation.
- NFPA 70, National Electrical Code — Governing U.S. electrical-code source; verify the edition adopted by the authority having jurisdiction.
- Eaton Bussmann Selecting Protective Devices Handbook — Supports conductor-protection context, NEC 240.4 next-size discussion, and the standard fuse ampere-rating list.
- Eaton Bussmann 2023 NEC Code Updates — Supports NEC Table 430.52(C)(1) motor branch-circuit short-circuit and ground-fault fuse percentages used by the calculator.
- Littelfuse POWR-GARD Technical Application Guide — Supports fuse voltage-rating, AC/DC application, interrupting-rating, and time-current selection considerations.
How the example was checked: the 18 A continuous-load example was recomputed directly as \(18\times1.25=22.5\,A\), mapped to the next standard rating used by the calculator, and reverse-checked against \(25/1.25=20\,A\). The same inputs and 25 A output are present in the finalized calculator implementation.
Fuse Size Calculator FAQ
These answers address common follow-up questions that arise after calculating a fuse ampere rating.
How do I calculate what size fuse I need?
Start with the applicable circuit current and the sizing method for that application. In this calculator’s general-load mode, the non-continuous setting uses 100% of load current and the continuous setting uses 125%, then the tool moves to a standard fuse rating. Motor branch circuits use a separate NEC motor percentage method. Always verify conductor, equipment, voltage, and interrupting-rating limits after the amp calculation.
Should a fuse always be 125% of the load?
No. The calculator uses 125% only for its continuous general-load setting. Motor circuits, transformers, capacitors, HVAC equipment, photovoltaic circuits, appliances, and other applications can follow different code or manufacturer rules. Treat 125% as an application-specific calculation factor, not a universal fuse rule.
Do I size a fuse to the load or to the wire?
Both relationships matter, but they answer different questions. The load establishes how much current the circuit must carry under the applicable sizing method. The conductor and equipment then constrain what overcurrent protection can be used. A fuse can be large enough for the load yet still be too large to protect the conductor or equipment.
Can I just round up to the next fuse size?
Do not treat upward rounding as unconditional permission. The calculator reports the next standard rating for its supported sizing method, but conductor protection, equipment limits, and application-specific code rules can prohibit that rating. NEC 240.4(B) has a specific next-higher-standard-rating allowance for conductor protection only when its conditions are satisfied.
How do I calculate fuse size from watts?
Convert electrical input power at the point being fused to current first. For DC, use \(I=P/V\). For single-phase AC real power, use \(I=P/(VPF)\). For balanced three-phase real power, use \(I=P/(\sqrt{3}V_{LL}PF)\). If the value you have is equipment output power, account for efficiency or use the manufacturer’s input-current rating. Then apply the sizing method that actually governs the circuit.
Why can a motor fuse be larger than the motor running current?
A motor branch-circuit fuse must tolerate normal motor starting current while providing short-circuit and ground-fault protection. NEC Table 430.52(C)(1) therefore permits percentage values above motor full-load current for many fuse/motor combinations. Separate motor overload protection addresses sustained overload conditions, so the branch fuse and overload device perform different jobs.
What is the difference between a time-delay and fast-acting fuse?
A time-delay fuse is designed to tolerate certain temporary overcurrents, such as normal starting or inrush current, longer than a fast-acting fuse of comparable ampere rating. The exact behavior comes from the manufacturer’s time-current curve; the words “time-delay” or “fast-acting” do not make all fuse families interchangeable.
Can I use an AC fuse in a DC circuit?
Only if the specific fuse is rated for the required DC voltage and application. Littelfuse notes that fuses can be rated for AC only, DC only, or both. Do not infer a DC rating from an AC voltage marking; verify the manufacturer’s published DC rating.
Does the fuse voltage rating matter if the amp rating is correct?
Yes. The voltage rating relates to the fuse’s ability to interrupt the circuit safely after the element opens. The fuse voltage rating must be at least the circuit voltage, and the device must be rated for the applicable AC or DC system.
What is fuse interrupting rating?
Interrupting rating is the fault-current level the fuse is designed and tested to interrupt safely under its rated conditions. The fuse interrupting rating must equal or exceed the available fault current at its installation point. A fuse with the correct normal ampere rating can still be unsafe if its interrupting rating is too low.
Why does a fuse keep blowing even when the calculated size looks correct?
Possible causes include normal inrush exceeding the fuse’s time-current capability, an incorrect fuse class or characteristic, excessive ambient temperature, loose or high-resistance connections, repeated pulse loading, or an actual equipment fault. Check the current waveform and manufacturer time-current data before increasing the fuse rating.
Is a fuse size calculator enough for a final electrical design?
No. The calculator is useful for sizing and screening, but final selection can require the adopted code, conductor ampacity and installation conditions, equipment instructions, fuse class and holder data, voltage and AC/DC suitability, available fault current, interrupting rating, coordination, and application-specific protection requirements.
How do I size a fuse for a 12 V, 24 V, or 48 V DC circuit?
Calculate the DC operating current with \(I=P/V\) when electrical input power is known, or use the measured/rated current directly. Then apply the protection rules for the actual application and verify conductor ampacity, equipment limits, fuse voltage/DC rating, and interrupting capability. Automotive, RV, marine, battery, solar, and NEC building-wiring applications should not be treated as one universal fuse chart.