Blue Sea Systems MRBF Terminal Fuse 250A 58V DC

The Blue Sea Systems MRBF Terminal Fuse is a space-saving, ignition-protected fuse built for main battery circuit protection on boats with large battery banks, including lithium-ion setups. At 250A and 58V DC maximum, it's sized for the main feed off a house or start battery rather than a branch circuit.

Key features

• 250A rating, 58V DC maximum
• Interrupt capacity of 10,000A at 14V DC, 5,000A at 32V DC, and 2,000A at 58V DC
• Ignition protected per SAE J1171 — safe for installation in a gasoline engine room
• IP66-rated housing with a clear window for a visible blown indicator
• Color-coded by amperage for quick identification

This fuse is not a standalone part — it must be installed in a Blue Sea Terminal Fuse Block (PN 5191 or PN 2151), which bolts to the battery terminal and holds the fuse in place. Never mount the MRBF fuse directly to a battery post.

It's a common upgrade for boats moving to a Class T or ANL-protected main circuit but wanting an in-line, ignition-protected fuse right at the battery terminal, satisfying ABYC main-circuit protection requirements for large battery banks.

Because the MRBF sits directly at the battery, it's often the first line of defense on lithium-ion and TPPL banks that can deliver very high fault currents — pair the amperage rating to the battery manufacturer's recommended main fuse size, not just the wire gauge, since battery-side short-circuit currents can be higher than a typical branch-circuit calculation would suggest. Keep the color-coded body visible after installation so the rating can be confirmed at a glance during a haul-out or survey.