Blue Sea Systems · 5191
MRBF terminal fuse holder wiring diagram
Blue Sea 5191 single MRBF holder, 30–300 A and 58 V DC maximum; fuse sold separately. Mounts on a 3/8-inch battery or busbar stud, with an M8 output stud. Interrupt capacity and ignition protection depend on the installed fuse.
Wiring diagram
How the MRBF holder is wired.
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Cable sizing for this example
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Installation notes
Before you install.
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Verified against the manufacturer's documentation, checked 2026-10-01. Manufacturer documentation →
What is included in Blue Sea 5191?
The 5191 is a single MRBF terminal fuse holder. Its fuse is sold separately. The official product reference and original mounting/dimension drawings establish its 30–300 A fuse range, 58 V DC maximum and physical connections. The manufacturer supplies installation drawings for this part; no separate model-specific PDF manual was found.
The holder's 300 A maximum does not select a 300 A fuse for the circuit. Select the fuse for the conductor and connected equipment before purchasing the holder/fuse combination.
How do IN and OUT map to the hardware?
IN is the holder's battery-side mounting connection. OUT is the isolated upper stud carrying the protected outgoing cable lug. The mounting drawing shows the holder on a 3/8-inch battery or busbar stud and a 5/16-inch ring terminal above the fuse position.
The isolated stud and fuse establish the intended current path. Do not omit the holder and clamp a bare MRBF fuse directly onto the battery terminal. Do not place the outgoing lug on the battery-side mounting foot, where it would bypass the fuse. Use the specified stack, keep the insulating cap fitted and allow clearance for the battery cover and neighbouring terminals.
Where does the interrupt rating come from?
It belongs to the installed fuse, at its specified DC voltage. For example, Blue Sea's 5190 300 A MRBF reference lists 10,000 A at 14 V DC, 5,000 A at 32 V DC and 2,000 A at 58 V DC. Those are not one universal 10 kA rating across all battery voltages.
Confirm the exact fuse's interrupt capacity against the prospective battery fault current, including parallel strings. A holder, BMS or current-limited normal load does not establish that fault-current value. The manufacturer's ignition-protection claim is conditional on using its MRBF terminal fuse with the holder.
What must be checked during installation?
The holder's output stud maximum torque is 75 in-lb (8.47 N·m). That value does not override the battery manufacturer's limit for the separate battery-terminal connection. Support the cable so the fuse assembly does not carry its mechanical strain.
Inspect the actual fuse and terminal stack before energising. The catalog's two terminals do not show the fuse's current marking, interrupt rating, battery-post hardware or spare-fuse provision. Source-mounted protection still requires those choices to be documented for the installation.
Fit check
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Technical reference
Specifications and terminal map.
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Catalog specification
Blue Sea 5191 single MRBF holder, 30–300 A and 58 V DC maximum; fuse sold separately. Mounts on a 3/8-inch battery or busbar stud, with an M8 output stud. Interrupt capacity and ignition protection depend on the installed fuse.
Connection limits are listed in the terminal map. Use the manufacturer's documentation for the full specifications.
Terminal map
Catalog connection points, current direction and planning limits. Check the manufacturer's pinout and connector ratings before installation.
in
positive · input
out
positive · output
Sources and sizing method
Equipment specifications. Model details, ratings and terminal roles come from the catalog. Check your unit’s label and current manufacturer documentation for its exact revision.
Example sizing. Wire sizes and fuse ratings apply to the connected example, not a fixed cable size for this component. Set your actual equipment, current, lengths and installation conditions in Crimp before choosing hardware.
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