I commented on your previous post, I'm doing basically the same install as you (2x100 to Victron 75/15, but wired in parallel rather than series). Hooked up on Saturday and it's working great.
As others said, Victron 75/15 will take 10 gauge. That's what I have in it. The manual shows that in section 5 > Power Terminals: 6 mm^2 / AWG10.
The 20a fuse on the controller protects the controller itself. I confirmed this with Victron support, but after thinking about it more it's a slightly silly question because device fuses
always protect just the device - think about what would happen if the wires pulled out of the device and started flopping around, contacting a ground.
I would not step down to 14 gauge wire because that's now the weak link in your circuit, mostly defeating the purpose of your 8 gauge. I also would not use 8 gauge when 10 gauge is sufficient, but if you already got it, it's fine. There's no benefit to "over protecting" a circuit and I don't think 8 gauge is providing additional safety
here. That's a myth that seems to get often propagated.
Oversizing is sometimes beneficial to reduce voltage loss over long runs. However there's debate over how beneficial that really is with solar panels
, and personally I would go with what the controller manufacturer designed their controller for. (10AWG). There's no real harm in doing 8AWG, other than wasting a bit of money
and introducing a step-down connection which is an additional failure point.
You asked "so then there should also be a fuse on the pos lead from the panels, right?" No, because solar panels
are a current
limited source. There were some other helpful CF threads on this which helped me understand:
(see posts by ramblinrod, he knows what he's talking about)
Regarding your wire run from batteries
to controller being only 2 feet long, and what's the point in fusing something so short? I also had that question, because mine is also only 2 feet, and well secured - it's hard to imagine how a dead short would ever occur on a 2' run. But ABYC says 7" from battery, and if you have high amp MRBF fuses on your batteries already, those are *not* protecting 14 gauge. So I put a 30a fuse a few inches from the pos distribution point (PowerPost).
Fusing is mainly about reducing a very low probability to an even lower probability.