Blue Sea Systems 225A-400A Class-T Fuse, Up to 125Vdc, 20kAIC for Residential or Mobile Energy Systems

About the Blue Sea Systems Class-T Fuse

The Class T is the highest-AIC fuse commonly used in marine, RV, and residential battery systems. At 20,000A interrupt capacity, it can safely open under fault currents that would weld an MRBF (10,000A AIC) or ANL (6,000A AIC) fuse shut. Its fully metal-encased construction and extremely fast response time make it the fuse most inverter manufacturers specify for the DC input circuit, and the fuse ABYC E-13 specifically calls out for lithium battery installations.

Why Class T for Lithium

LiFePO4 batteries have very low internal resistance compared to lead-acid, which means they can deliver enormous short-circuit currents. The fuse needs to be able to safely interrupt that current without welding shut or failing dangerously, and that's what AIC (Ampere Interrupt Capacity) measures.

AIC ratings are voltage-dependent. A fuse that can interrupt 10,000A at 14V may only handle a fraction of that at higher voltages because the arc is harder to extinguish. The MRBF fuse illustrates this clearly: it's rated at 10,000A AIC at 14V, but only 5,000A at 32V and 2,000A at 58V. The Class T is rated at 20,000A AIC at 125V DC, meaning it maintains its full interrupt capacity across 12V, 24V, and 48V systems.

At 12V, MRBFs can handle most individual lithium batteries because the combination of low voltage and 10,000A AIC provides adequate margin. At 24V and 48V, the MRBF's effective AIC drops to the point where even modest lithium banks can exceed it. A 48V battery with low internal resistance can easily produce short-circuit currents well above the MRBF's 2,000A rating at that voltage. This is why ABYC E-13 specifically calls out Class T for lithium installations, and why most inverter manufacturers spec Class T on the DC input.

For 12V systems with smaller individual batteries, per-battery fusing with MRBF terminal fuses can still be a viable and more economical approach, since each fuse only sees the short-circuit current of one cell at a voltage where the MRBF's AIC is strongest. But for 24V systems, 48V systems, or any bank-level fusing on lithium, Class T is the correct choice.

Compatible Fuse Blocks

Class T fuses require a dedicated fuse block. Current Connected carries two options:

• Blue Sea Systems Class-T Fuse Block (available in standard and ignition-protected variants). Accepts one fuse, rated to 160V DC with M10 terminal studs. Fits up to 4/0 AWG cable.
• Victron Lynx Class-T Power In provides two Class T fuse positions inside a 1000A busbar module. Integrates with the Victron Lynx modular distribution system and reports fuse status through a Cerbo GX.

Fuse Sizing

Size the fuse to the wire you're protecting, not just to the expected load. Continuous load should not exceed 80% of the fuse rating. Like MRBF and ANL fuses, Class T fuses have a time-delay curve that allows brief inrush spikes (motor starting, inverter surge) to pass without nuisance blowing. A 300A Class T can handle well over its face value for short durations. Check the manufacturer's trip-delay curve when sizing for circuits with significant inrush.