Blue Sea Systems Dual MRBF Terminal Fuse Block 30-300A

The Blue Sea Systems Dual MRBF Terminal Fuse Block extends the same at-the-battery fusing concept as the single-position 5191 block, but lets two separate circuits share one 3/8" terminal stud. It's a space-efficient way to fuse a house bank and a windlass or bow thruster circuit, for example, without stacking multiple single blocks.

Key features

• 300A maximum, 58V DC maximum, per position
• Mounts on 3/8" terminal studs; isolated M8 output studs accept 5/16" ring terminals
• Insulating cap prevents accidental shorts
• Ignition protected only when paired with Blue Sea MRBF Terminal Fuses

Each position takes its own MRBF fuse, sized independently for the circuit it protects — the two positions don't need to run the same amperage. As with the single block, this satisfies ABYC's 7-inch main-circuit-protection rule by fusing right at the source rather than partway down the cable.

Because both positions share the same base stud, double-check total current draw doesn't exceed what the underlying battery post or bus bar is rated to carry, and torque the mounting stud to 75 in-lb.

A common pairing is a house bank circuit on one position and a windlass or bow thruster feed on the other, each fused independently at its own rating right at the source. As with the single-position block, size each MRBF fuse to the connected battery's maximum discharge current — not just the wire gauge — and keep spares on hand for both positions since a blown fuse must be replaced rather than reset. Blue Sea's Dual MRBF block is a popular upgrade when adding a second high-current circuit to a battery that already has a single MRBF block installed, since it replaces the single block without needing a second stud location.