Between Solar Controller & Batteries, What?

My 30A solar controller recommends a 40A fuse between controller and batteries and another between controller and panel(s).

Thank you EVERYONE for the responses. A special thanks to bka0721 of the fuse/switch I wanted to use but had not found any mounting Pics. Wiring is setup for more panels in the future if desired. Also found little cost difference, IMHO, between the heavier gauge wire and the lighter so went with the heavier as recommended by HandyBob.

Thanks again,
rocmoc n AZ/Mexico

Some here have used these:

Inline Circuit Breakers

Every wire connected to a battery's positive terminal needs a fuse or breaker (your choice) as close to the battery as possible. If the wire ever shorts to ground it will cause lots of heat, sparks, exploding batteries, etc. if it's a big enough wire.
I would never recommend "letting the wire be the fuse". That means "letting the wire heat up, melt, and burn". That's not something I want happening in my RV.

I have two Buss Blade Fusses for both of my Morningstar MPPT Charge Controllers, as seen in this recent photo. Both are on the Positive (+) leg. I also have a Blue Sea Disconnect on the leg for my PSW 2000w Inverter (shown)

b

AM Solar installed a simple disconnect switch at my request on my system.

Hi,

I have a switch and a fuse on the positive.

The controller installation manual will tell you what you should do. What actually gets done can be different :)

Some say if the wires are not into a wall where you can't see if they are melting, it is ok not to fuse them and just let the wire be the fuse, since it won't cause a fire in a wall you can't see. Others say to just do what you are told.

Those wires of yours are way overkill for the solar job, so you only need to fuse against battery failure. Not sure what the proper size fuse would be for three feet of #2 at whatever amps. Pick something a little over (1.25 times is often recommended) the max expected amps from controller to battery.

I have my solar to battery join in at a buss where closer to the battery there is already a fuse on that pos wire. With a buss you are supposed to have a big fuse to the battery that takes all the amps coming into the buss and then each "branch" (one would be your solar) gets its own fuse before the buss, sized according to the max amps of that branch.

The solar would usually have a smaller fuse than the converter's and the inverter's would be quite big. Then you add all those input amps up and fuse the last wire to the battery from the buss for that total. NEC in the States wants 1.25 margin for fuses above expected amps IIRC (check it out if important to you--I am not sure exactly)

Just wire.

About 2' of #4 and a 70 amp Maxi-Fuse.