Fuse Sizing for Victron System

[AndyRonLI]

Folks
I am putting in a multiplus-II in my fifth wheel.
I am using the Lynx 1000 Shunt and Lynx 1000 Distributor
I will be starting with two connections to the Distributor, one for the mulitpluss and one for the trailer loads
The mulitpluss fuse on the distributor works out to 325 amps based on a max continuous current of 255

It is not completely clear, but I am guestimating that the coach loads would work out to fifty to 75ish max
The current coach loads pull on a 6 gauge wire.
So check my guess work.
The awning, Leveling Jacks, and slide motors are all protected by a common 30 amp shortstop automotive type thermal breaker
The tank heater is protected by a 30 amp shortstop breaker.
The coach wiring (led lights, furnace, fans etc) are protected by a 50 am shortstop automotive breaker.

The only long term continuous load I could see, would be the tank heaters and the coach at say 50%. Everything else is intermittent.

I have four 200ah batteries in parallel

So my fuse plan would be
Lynx-distributor to/from multiplus: 325 amps
Lynx-distributor to/from trailer buss: 75 amps
Lynx Shunt: 400 amps (too high?)

Wiring Plan:
Lynx Distributor to/from multiplus: 2/0 (Peak current is 250, so this seems slightly undersizesd but it is what Will used)
Lynx Distributor to /from trailer buss: AWG 6 ( that is what the current system uses, so going to call it OK)
Lynx Shunt to / from battery bank: 4/0?
Battery to battery interconnects: 2/0

Some how this seems like the fuses are higher rated than the cabling?
Am I missing something?
Thanks
ANdy

 

[Adam De Lay]

What's the specific model MultiPlus-II you're putting in?

 

[justinm001]

Some how this seems like the fuses are higher rated than the cabling?

Yes you're correct 2/0 should be under 200amps and 6 should be max 75amps. Main fuse should be rated to the source battery wire.

https://www.cerrowire.com/wp-content/uploads/2021/04/Cerrowire_Ampacity_Chart_210405.pdf

Wire rating should meet or exceed fuse rating. The point of the fuse is to blow when you exceed the wire rating so the wire doesn't melt.

You can always go bigger wiring as big as will fit.

 

[AndyRonLI]

What's the specific model MultiPlus-II you're putting in?

its the 12-120/2

 

[AndyRonLI]

I guess whats bothering me is that a 3000VA inverter at 92% efficiency and 12.8 V (20% state of charge) should be at 255 Amps continuous.
That would be a 4/0 wire, but I see a lot of installs using 2/0. Is it just that the run is so short.
The Blue Sea calculator

Circuit Wizard - Blue Sea Systems

At 2 ft with 1% voltage drop selects 2/0 for 95C with 325 amps continuous, the charts get you much bigger conductors.
That seems a better choice for the Multiplus to Distributor
I like that tool!

Andy

 

[Adam De Lay]

From my limited understanding, cable current rating is based on the gauge, temp rating, length of cable and the type of shielding used on on the cable. Seems like if you have the right temp rating, you could get away with 2/0.

I know I've been frustrated in the past. Seems like every chart you see out there has different ratings for different sizes.