Fusing for 4/0 wire. From battery to 24v 3000w inverter -

[Derka181]

I’m on a 12v offgrid system with 400ah of batteries and a 2000w inverter. I have two systems. I’m upgrading one system to 24v with a 3000w inverter and the other system will be a 48v system 6500w inverter. I will be using 4/0 wire for all my new setups because I have a lot of extra cable. My question is do I fuse to the size of the inverter or do I size my fuse to the max amps of the wire (4/0).

So what size of fuse would you use between the 24v system with a 3000w inverter? Using the 4/0 wire.

 

[Ampster]

Fuses are to protect the wire so generally the fuse is matched to the current carrying capacity of the wire. However one can always used a smaller fuse if you do not think the current drawn or used will exceed that value. The advantage of higher voltage systems is the current is often less. A 24 volt inverter drawing 3000 Watts will only pull 125 Amps. Similarly a 6500 Watt inverter at 48 volts is less than 150 Amps.

 

[OffGridInTheCity]

To re-iterate @Ampster's comment. Fuses (and breakers) are to "protect the wire", not the loads. Every load such as an inverter or refrigerator or cooktop or water heater or whatever... is responsible to have it's own protection - fuses or breakers or even just burn thru as in a filament light bulb.

So just think - protect the wire - and you'll always be on the right track

 

[zanydroid]

There’s a notion of maximum overcurrent protection though on a circuit. If not printed on the appliance nameplate NEC has a formula for what you need to use.

IIRC for regular 120V appliances the formula works out to 20A or 25A depending on the amps drawn by the appliance.

 

[time2roll]

24V 3000W I would be at 150a class-T
Same for the 6500 at 48v.

200 amp is fine also. I would keep them the same so a single spare could serve both.
Class-T will pass 200% for 30 seconds for surge performance.

While the above posts are correct I still prefer to keep my fuses a bit tight.