Blue Sea Systems MRBF Fuse Block, 58V DC, M8 Stud

Overview

The Blue Sea Systems MRBF Terminal Fuse Block is a range of fuse blocks for placing high-amperage DC circuit protection close to the power source on a boat. These blocks use MRBF terminal fuses and are suited to battery mains, inverters, windlasses, bow thrusters, battery chargers, and other DC loads where space is limited and short-circuit protection needs to be close to the battery, switch, or bus bar.

The listed configurations are rated for up to 58V DC. The single and dual terminal-mounted versions handle up to 300A, while the surface-mount three-circuit versions are rated up to 240A per circuit, with the common-source version also rated up to 300A per block.

This product family is useful when a boat owner, installer, or refit yard needs MRBF fuse protection without adding a larger fuse block panel. The range includes non-ignition-protected terminal styles and ignition-protected surface-mount styles, so the correct version depends on the circuit layout and mounting location.

Key features

• Uses Blue Sea Systems MRBF terminal fuses for high-current DC circuit protection; fuses are sold separately.
• Supports 58V DC systems, covering common 12V, 24V, and 48V marine DC installations when the rest of the system is specified correctly.
• Single and dual terminal versions mount on 3/8 in terminal studs and accept 5/16 in ring terminals.
• Surface-mount versions accommodate three MRBF fuses for grouped circuit protection in charger, bus, or multi-load layouts.
• M8 5/16 in terminal studs provide a familiar connection point for appropriately sized marine lugs.
• Insulating caps or covers help reduce the risk of accidental shorts at exposed high-current connections.
• Ignition-protected versions are available for installations that require ignition protection around gasoline-powered vessels or machinery spaces.
• The surface-mount independent-source and common-source versions use M5 #10 mounting hardware and include label recesses for circuit identification.

Variants

The product is offered in four configurations that change the circuit layout, mounting approach, and ignition-protection rating.

Across the listed configurations, the shared electrical limit is 58V DC and the cable connection studs are M8 5/16 in. The fuse arrangement, source layout, current rating, and ignition-protection rating vary by part number.

• 2151: Dual type, not ignition protected. This terminal-mounted version provides two MRBF fuse positions and is rated up to 300A total, which suits compact battery-post, switch-stud, or bus-bar protection where two fused outputs are needed from the mounting point.
• 5191: Single type, not ignition protected. This terminal-mounted version covers one MRBF fuse position and is rated up to 300A, making it a straightforward choice for one protected high-current DC feed.
• 5194: Independent Source type, ignition protected. This surface-mount version accommodates three MRBF fuses with independent source wiring, a layout commonly used with multi-output battery chargers or separate incoming feeds.
• 5196: Common Source type, ignition protected. This surface-mount version accommodates three MRBF fuses from one common source and distributes that source to three separately fused loads.

Installation and fit

The terminal-mounted versions are intended for compact installations at a battery post, battery switch stud, or bus bar stud where overcurrent protection needs to stay close to the source. They use standard M8 hardware at the fuse connection and allow terminal stacking when the installation layout and hardware stack height are appropriate.

The surface-mount versions are better suited to a fixed mounting location near a battery bank, charger, or DC distribution point. Their wiring layout allows cables to exit from one side, which helps keep high-current cabling organized in tight lockers, under-seat battery compartments, and electrical panels.

Fuse rating, cable size, lug size, and torque should be matched to the actual load and installation standard for the vessel. MRBF fuses should be used with the proper fuse block rather than mounted directly to a battery terminal.

Electrical and system integration

This is DC power protection hardware, not a data or instrument-network connector. It does not connect to NMEA 2000, NMEA 0183, or other marine electronics networks. Its job is to protect high-current conductors by placing a correctly rated MRBF fuse close to the source of power.

For refits and new electrical builds, the range works well where a full panel-style fuse holder would take too much space or where the protection point needs to be right at the battery, switch, bus bar, charger, or load distribution point.

Protection and serviceability

The insulating cap on the terminal versions and the clip-on cover on the surface-mount versions help shield energized hardware from accidental contact. On the surface-mount models, label recesses make it easier to identify circuits during service, troubleshooting, or battery charger maintenance.

Because the fuses are sold separately, the installer can select the MRBF fuse rating that matches the protected conductor and connected equipment. This keeps the fuse block flexible for different marine DC loads while still using one consistent MRBF fuse format.

Orders are processed within 2 business days, which includes verification, packing, and dispatch. Orders of $100 or more qualify for free shipping when eligible. For orders under $100, shipping costs are calculated at checkout based on destination, package weight, and selected service. International shipping is available for eligible products, and certain items may require additional handling, warehouse transfers, or may ship directly from the manufacturer, which can affect processing time.

Deliveries are handled by preferred carriers such as USPS, UPS, FedEx, DHL, and others depending on your location and selected service. Estimated delivery times are displayed at checkout and may vary due to customs processing, carrier delays, weather, postal disruptions, or other circumstances beyond our control. Once your order ships, you'll receive a confirmation email with tracking information. Tracking may take up to 24 hours to update on the carrier's website and is also available through your account when applicable.

We ship throughout the United States and to most international destinations for products eligible for international shipping. International orders may be subject to customs duties, taxes, brokerage charges, or other import fees, which are the customer's responsibility and are not included in the product or shipping price. PO Boxes are accepted only when shipping through USPS, and not all packages qualify for this option. If your order does not arrive within the estimated delivery window, please contact us at info@apollolighting.com or +1 (954) 375-0100 so we can assist with locating your package.

Learn more.

Returns may be requested within 30 days of receiving your order. Items must be unused, uninstalled, unaltered, and returned in their original packaging with all tags, packing materials, blank warranty cards, manuals, instructions, accessories, and included items. Certain products, including installed or used electronics, electrical components, lighting, consumables, custom or special-order items, cut-to-length products, safety equipment, and merchandise exposed to water or marine conditions, may not be eligible for return.

To request a return, sign in to your account and select the applicable order and items, and submit your request for review. Eligible unfulfilled items may also be submitted for cancellation within 1 hour of placing the order. Returns or cancellations are not considered approved until you receive confirmation from Apollo Lighting. Please do not ship or drop off merchandise before receiving return approval and instructions.

Customers are responsible for arranging and paying for return shipping unless the return is due to an error by Apollo Lighting or the item is verified as defective, damaged, or incorrect. Missing, damaged, defective, or incorrect items must be reported within 2 business days of delivery, and photos or other documentation may be required for review. If the issue is verified, Apollo Lighting may provide or reimburse return shipping and issue a replacement or refund depending on the circumstances. International customers are responsible for return shipping, duties, taxes, customs charges, brokerage fees, and other costs associated with an international return.

After your return is received and inspected, approved refunds are issued to the original payment method and may take 5-7 business days to appear after processing. Original shipping and handling charges are nonrefundable, and the value of any included free items that are not returned may be deducted from the refund. Apollo Lighting does not charge a standard restocking fee on eligible returns. Returns that are incomplete, damaged, installed, used, altered, improperly packaged, or otherwise do not meet the eligibility requirements may be refused. We recommend using a trackable and appropriately insured shipping service for all customer-arranged returns.

For assistance, contact info@apollolighting.com or call +1 (954) 375-0100.

Learn more.

Many products sold by Apollo Lighting include a manufacturer's warranty covering defects in materials or workmanship. Warranty terms vary by brand, product category, and model, so eligibility, coverage duration, exclusions, and available remedies are determined by the applicable manufacturer. We recommend reviewing the warranty information provided with your product before installation or use, especially for marine electronics, navigation equipment, lighting, electrical systems, pumps, safety equipment, and other specialized marine products.

If you need warranty service, the claim must follow the process established by the manufacturer, authorized service center, or designated warranty provider. You may be asked for proof of purchase, a serial number, product registration, photos, maintenance or installation records, or other documentation. Apollo Lighting does not determine or modify a manufacturer's warranty coverage or final claim decision, but we are happy to help provide purchase information and direct you to the appropriate manufacturer or warranty resource.

Keep your receipt, product documentation, serial number information, and original packaging when practical. Damage caused by normal wear, misuse, improper installation, insufficient maintenance, corrosion, impact, unauthorized modifications, electrical issues, or operation outside the manufacturer's specifications may not be covered. Warranty claims are separate from standard returns, so a product that has been installed, used, or exposed to marine conditions may no longer qualify for return while still remaining eligible for evaluation under the manufacturer's applicable warranty.

Learn more.