BOJACK MRBF Terminal Fuse Block 250A Waterproof
$22
Key Specs
| fuse-type | MRBF Terminal Fuse |
| amperage-range | 30-300A (250A supplied) |
| voltage-rating | 32V DC |
| material | Marine-grade housing with brass contacts |
| mounting | Bolt-on battery terminal stud |
| waterproof | Yes |
Pros
- ✓ Waterproof housing suits harsh marine and outdoor environments
- ✓ Compact MRBF footprint mounts directly on battery terminal
- ✓ 250A rating handles large inverter and windlass loads
- ✓ Budget price compared to Blue Sea Systems equivalents
Cons
- ✗ Brand has less field history than Blue Sea or Littelfuse
- ✗ Fuse availability at local stores may be limited
Detailed Review
Overview
The MRBF (Marine Rated Battery Fuse) format was designed for one purpose: to sit as close as physically possible to the positive battery terminal and interrupt a fault current before it can ignite wiring insulation or cause a fire. The BOJACK 250A MRBF terminal fuse block delivers this critical protection in a compact, waterproof package at a price that undercuts the major marine brands.
MRBF fuses are a direct-mounting design — the fuse block bolts onto the battery post itself, so there is essentially zero unprotected cable between the battery and the first overcurrent device. ABYC and NFPA 303 guidelines for marine electrical installations strongly recommend — and often require — fusing within 18 inches of the positive terminal. MRBF accomplishes this better than any in-line fuse holder.
Installation and Wire Sizing
Installation is straightforward: remove the positive terminal bolt, slide the MRBF block over the post, reinstall the bolt, and connect your main positive cable to the fuse block’s output lug. The 250A rating suits main feeder cables sized at 2/0 AWG or 3/0 AWG, which are typical for 12V systems with inverters up to 3000W or combined loads exceeding 150A continuous.
The fuse block accepts ring-terminal connections on the output side, making it compatible with standard marine wiring practices. Torque the terminal bolts to spec and apply a thin layer of dielectric grease to resist corrosion in bilge and engine-bay environments.
Which Systems It Fits
The 250A MRBF is well suited to RV house battery banks, marine auxiliary systems, and van conversions running moderate inverter loads. If your system draws more than 200A continuous — for example, a 2000W+ inverter on a 12V system — size up to a 300A fuse to stay within 80% of the fuse rating for sustained loads. For lithium battery banks, MRBF fuses are an excellent match because LiFePO4 cells can deliver very high instantaneous current; the MRBF interrupts faults faster than many ANL designs.
ANL vs. MRBF: When to Choose MRBF
ANL fuses mount in-line along the cable run and are easier to access for replacement. MRBF fuses mount at the battery terminal, which is the safest placement electrically but requires removing the terminal post for fuse changes. For systems where the battery bank is accessible, MRBF is the preferred choice for new builds. ANL is often a better retrofit when the battery is buried behind a wall and terminal-post access is difficult.
Who It’s For
This fuse block is ideal for budget-conscious builders who need proper terminal-post overcurrent protection without spending $40–60 on a Blue Sea Systems unit. It is appropriate for RV solar systems, boat auxiliary banks, and van builds where waterproofing is a requirement and the 250A rating aligns with the main cable size.
