12volt terminal fuse block

I use them in my Land Cruiser. I think they were originally designed for marine applications. I mount them directly to the batteries. They're call MRBF fuses.

They take up less space than alternatives. There is a double one too. They go up to about 300A so I use them for the winch and joining batteries.

Double fuse holder

Fuses can be expensive and hard to get, though Jaycar has a good range, and keep a few spares.

Recommended by many boaties, Nick.

You can buy them at Whitworths too, a reputable boating supply outlet here.

Bob

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There is a problem with these MRBF type fuses……….

The construction of the fuse incorporates a ceramic component in the path of the clamping force. The fragility of this ceramic limits the clamping force and the fuse manufacturer specifies the nut torque force to be 15 inch-lbs (8.47Nm). This is a very low clamp for 8mm stud connections carrying typical currents for the application. Lug tightening specifications for such stud/cable sizes typically nominate torque as much as 19 ft-lbs (27Nm) which is considerably higher than the MRBF limitation. Note that was 19 ft-lbs NOT inch-lbs.
To make matters worse, the MRBF has a fibre washer above the lug and in the clamp path.

Electrical industry standards prohibit non-metallic components in the clamping path. In respect to Terminal Connections, AS/NZS 3000 states…. "Clamping shall not depend for its effect on pressure on non-metallic materials …"

In the past, I had considered using MRBF fuses but on inspecting their construction I decided not to and still would not use them despite their apparent convenience and even though I have seen no expressions of problems. They do not comply with good electrical engineering practice or Standards.
MRBF fuses are offered up to 300A. At 15 inch-lb torque?? No way in my book!!

DISCLAIMER: Note that the above is not offered as professional advice, simply my opinion and actions. lol

Nick.

What auxiliary system needs 300 Amp fuses?
I don't know what starter motor your boat has but if the starter draws plenty of current on startup, then the fuse is taking all of that. If it isn't in the starter path, why have a 300a fuse anyway. I would prefer a few smaller fused circuits supplying devices etc.

Even if the fuse IS to be used in the start circuit or NOT, I would, even for normal engines, ie, in vehicles too, service the starter motor so the bearings are lubricated with a decent lubricant, ie, Telfon grease where applicable and Mobil 1 or similar, which doesn't dry out like many others do, on bushed and Felt oiler pads. That way you will have far less internal friction in the starter as it will crank faster than before and for less time., AND with less current draw. So why have a 300A fuse in the circuit?
Even apply some Moly spray to the ring gear and / or starter pinion teeth as that will further reduce cranking friction.
Recently I serviced my 12 yo, Toyota Corolla which was using too much crank amps and was slow. Doing the above made the engine crank much faster.

I have had the opportunity to examine a number of these type circuit breakers labelled "WATERPROOF" and non of them exhibited waterproof construction.
In fact I had a pair under the bonnet of the Troopy and one became unreliable. I opened it up to see why and found the enclosure to contain considerable very fine dust. I replaced them with fuses.