Advice for circuit breaker size for 12V vehicle DCDC/solar system

[KrispyHolmes]

Hi, I've gathered most of the parts for building a 12V dual battery system using Renogy products. It's very similar setup to the '400Watt solar package with alternator charging' https://www.mobile-solarpower.com/simplified-400-watt-fewer-wires-and-alternator-charging.html

I have a question on the size of the circuit breaker that goes from the battery to the inverter and the fuse block. I'm planning to wire it the same as Will's picture, with the inverter (1000W) and the fuse block (100amp, but probably only ever max 50A in use) feeding off the same manual reset circuit breaker.

My first question is what size circuit breaker do I need?
I'm a little confused as some parts of Wills instructions say 'size this breaker to the inverter' and some say 'size to the inverter and fuse block'. I figure it needs to be sized as if both inverter and fuse block were fully loaded at the same time right? So 1000W/12V (approx 83A) for the inverter + 50A for the fuse block. So 133A x 1.25 = 166A. So either a 150A or 175A breaker (as its pretty unlikely I'll be drawing 50A from my fuse block).

My second question is what size wire to the fuse block?
I'll be running 3AWG to the inverter (it needs 4AWG, but being conservative). If I'm using a common circuit breaker servicing both the inverter and the fuse block, then I'm thinking I need the same size cable to the fuse block as the inverter...correct? Because is there is a short-circuit in the fuse block or cable to the fuse block, the breaker will only trip at 150A. If the cable to fuse block was 6AWG, then perhaps the cable would smoke/burnout before the circuit breaker tripped?

I guess the alternative to using a common breaker servicing both inverter and fuse block is to run a separate cable from the battery to the fuse block with its own fuse? Would that be correct?

Thanks in advance, Kris

 

[MisterSandals]

with the inverter (1000W)

Fusing:
1000W / 10V cutoff / .85 efficiency x 1.25 leeway = 147A fuse or breaker (aka 150A)

 

[chrisski]

I think you need a totally separate fuse for the DC leg to the fuse box. My fuse box which looks just like yours is rated to 30 amps. With the way you have it routed up to 150 amps can flow to it if the inverter is off.

For the 150 amp fuse, I would choose a wire and insulation off this chart based on ampacity. It has thicker wire than the blue see has.

 

[KrispyHolmes]

I think you need a totally separate fuse for the DC leg to the fuse box. My fuse box which looks just like yours is rated to 30 amps. With the way you have it routed up to 150 amps can flow to it if the inverter is off.

For the 150 amp fuse, I would choose a wire and insulation off this chart based on ampacity. It has thicker wire than the blue see has.

View attachment 87250

Thanks. Yes it would seem more simple to wore a separate cable from the battery (or terminal block) to the Fuse block. That block is a Blue Seas one rated to 100amp for the whole block. BTW - the picture is not mine, but taken directly from Will's 400watt solar with inverter charging' DIY recipe