Blue Sea Systems 2151 Dual MRBF Terminal Fuse Block, 30-300A, 58V DC, Mounts on 3/8" Battery Post or Bus Bar Stud, for Marine and Mobile DC Systems

About the Blue Sea Systems 2151 Dual MRBF Terminal Fuse Block

The 2151 provides two independently fused circuit positions on a single terminal mount. It threads onto any 3/8" (M10) stud, whether that's a battery post, battery switch terminal, or bus bar, and accepts two MRBF fuses so you can protect two separate load circuits right at the source. Typical use: fusing both an inverter feed and a windlass circuit directly off the same battery terminal, each with its own appropriately rated fuse.

Meeting the ABYC 7" Rule

ABYC E-11 requires overcurrent protection within 7 wire inches of the battery bank (or up to 72 inches if the conductor is in a protective sheath). The 2151 meets this for two circuits simultaneously by mounting directly on the battery post. Both cable runs get protection at the source with zero unprotected conductor between the battery and the fuse. For RVs and off-grid builds, the same principle applies even where ABYC doesn't govern: fusing at the source means no unprotected cable that can short and overheat.

Like the single block, the 2151 adds height to the battery post. Measure your battery compartment clearance before committing, especially in tight marine battery boxes.

How It Mounts

Both MRBF fuses seat into the block side by side. Each load cable attaches to the M8 (5/16") output stud on top of its respective fuse using a standard ring terminal. The isolated stud design allows stacking of ring terminals on each output, so you can split a single fused circuit to multiple loads if the fuse is sized to the combined draw.

An insulating cap snaps over the entire assembly to prevent accidental shorts. When the cap is in place and MRBF fuses are installed, the assembly is ignition protected and weatherproof.

When to Use the 2151 vs. Other MRBF Blocks

The 2151 makes sense when you need two fused circuits off one terminal but don't want to take up panel space with a surface-mount block. If you only need one fused circuit, the 5191 Single Terminal Fuse Block is half the price and half the footprint. For three circuits, the surface-mount 5196 Common Source or 5194 Independent Source blocks are better suited.

Pair this block with MRBF terminal fuses in the appropriate amperage ratings. Fuses are sold separately.