01 · Load
Carry normal current
Crimp's planning baseline applies 125% headroom to the larger entered charge or discharge current. The exact governing standard, equipment guidance and fuse time-current curve still decide the final rating.
Battery protection tool
LiFePO₄ fuse size calculator
A battery's amp-hour rating does not determine its fuse. Start with the circuit's continuous current and documented surge, keep the fuse within every conductor and equipment limit, then verify DC voltage and interrupt ratings for the exact fuse and holder.
Reviewed August 28, 2026Scope 12 V DC planningRule Exact manuals win
01Evidence checker
Four gates. One candidate. No guessed inputs.
Enter values from the load, battery, conductor, fuse and holder documentation. Blank is a valid—and safer—answer when a value has not been verified. Nothing entered here is saved.
02Selection logic
Amp rating and AIC answer different questions.
A fuse can have the right number of amps printed on it and still be unable to clear a lithium-bank fault safely. Every gate below must pass for the exact proposed device.
02 · Conductor
Protect the weakest limit
The rating must not exceed the installed conductor's ampacity after temperature, bundling and installation derating—or any lower equipment maximum.
03 · Device
Cover voltage and fault current
Both fuse and holder need adequate DC voltage ratings. The exact fuse's interrupt rating must cover documented or calculated prospective current at its location for the complete installed source.
04 · Location
Protect at the source
Confirm source-side placement and any permitted exception against the applicable installation standard and the component manuals. The BMS is not the branch fuse.
Amp rating
Will it carry the load without sacrificing the cable?
Interrupt rating · AIC
Can it open the available fault without arcing or welding?
Class T is often considered for high-fault-current lithium banks because exact products can carry high published interrupt ratings. It is not a universal answer: use the voltage and interrupt data for the exact fuse at the relevant DC voltage.
03Bank and placement
Check the fault source you actually built.
Parallel batteries can contribute to the same fault. A per-battery figure cannot prove the interrupt rating for a fuse that sees the complete bank.
- 01
Define the protected segment
Name the battery terminal, bus, conductor and load on each side of the proposed fuse. Decide exactly what that device is intended to protect.Stop here - 02
Use whole-bank fault data
For any multi-battery source, obtain prospective fault current for the complete configuration at the proposed fuse location. Do not multiply an amp-hour rating into a made-up short-circuit value.Stop here - 03
Verify the exact fuse and holder
Match part numbers, DC voltage, interrupt rating, terminal size, permitted cable stack-up and torque. Family names alone are not specifications.Stop here - 04
Place source protection correctly
Apply the governing standard and manufacturer instructions for proximity to the energy source, enclosed spaces, environmental exposure and any allowed exception. - 05
Protect parallel conductors
Review whether each battery or parallel string needs individual protection as well as the bank's main protection; the topology and applicable standard decide this.
04Sources
Verify against current primary documents.
Product ratings vary by series, voltage and certification. Open the current datasheet for the exact fuse, holder, battery and protected equipment before committing the design.
01Victron EnergyWiring Unlimited: DC wiringFuse current, voltage, speed, type and interrupt-rating selection criteria.02Blue Sea SystemsSelect a fuse and fuse holder for your DC product installationManufacturer guidance for continuous-load headroom and conductor protection.03Blue Sea SystemsClass T FusesPublished DC voltage and interrupt ratings for marine Class T fuses.04EatonBussmann series Class T fusesManufacturer specifications for Class T fuse families.05LittelfuseMEGA Fuse Series DatasheetVoltage, interrupt rating and time-current data for MEGA fuses.06LittelfuseFuseology selection guideFuse-holder temperature, enclosure and installation derating considerations.07LittelfuseFuses for energy storage systemsFault-current and protection considerations for multi-source energy storage systems.08Victron EnergyLithium Battery Smart: InstallationManufacturer guidance tying system current, cable rating and fuse rating together.09International Organization for StandardizationISO 23625:2025 — Lithium-ion batteriesPublished scope of the current small-craft lithium-ion battery standard.10American Boat & Yacht CouncilStandards Update, Supplement 65ABYC's published update covering lithium-battery installation requirements.