Logic behind Fuse Sizing for the Multiplus 3000/12/120

Q&A and troubleshooting
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Hi folks,

I’m trying to wrap my head around the logic for the fuse sizing for the Multiplus 3000/12/120.

The numbers give ~278A continuous from the battery (3000W ÷ 12V at 90% efficiency).

But Victron recommends a 400A MEGA fuse, yet the recommended cables (~100mm²) are rated well below 400A.

I understand the fuse needs headroom above continuous draw to avoid thermal fatigue from repeated surges. But that creates a window (~280–400A) where the cable isn’t protected by the fuse against sustained overcurrent.

Is the correct interpretation that the inverter is a self-limiting load — it shuts down on overload before the cable is ever at risk — so the fuse is purely for short-circuit protection, and cable overcurrent protection is effectively delegated to the inverter’s firmware?

I just can’t understand why we don’t fuse at 300A for the continous current and then also be able to protect the cable with the fuse. The 300A MEGA fuse should be able to ride through the surge current which lasts just a couple of seconds.

Appreciate any insight.

Shane

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Hi, I have had 2 x 200A mega fuses on each 95mm cable for over 6 years. I also have a 12/3000/120-16 inverter and it works fine.

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The MultiPlus has a peak power of 6000W that’s more than 500A for a few seconds.
It can also be overloaded to 130% for around 30min if the input voltage is stable.

The fuse is a short circuit protection.