Wire type selection for MPPT 100/30 connection

Been going through a similar exercise with my setup and wanted to get some thoughts from the community.

I'm running a Victron MPPT 100/30 and trying to nail down the correct cable spec for the run between the controller and my 100Ah LiFePO4 (Fogstar Drift). The 30A max output makes me think I should be fine with 6mm² (roughly 10 AWG equivalent) for the battery side, but I keep second-guessing myself when I see people referencing AWG sizing — the conversion isn't always straightforward and it can get confusing fast.

A few specific questions:

• Is 6mm² adequate for a short run (under 500mm) between the MPPT and a 40A inline fuse, then on to the battery?
• Should both positive and negative sides be matched in cross-section? I've seen some installs where the negative is undersized
• Anyone using tinned copper rather than plain copper for their runs? Worth the extra cost in a potentially damp environment?

The Victron manual specifies up to 35mm² terminals on the 100/30 which suggests they're accommodating much heavier setups, so I don't want to over-engineer it unnecessarily.

I'm not doing any EV charging through this particular circuit just yet, but future-proofing is always at the back of my mind.

Curious what others have actually run in practice — particularly anyone who's had a BMS trip or thermal issue that traced back to underspecced cabling. Real-world experience tends to cut through the theory pretty quickly.

@NeilEdwards looks like your post got cut off before you finished the spec details — worth editing to include the run length and your panel arrangement, as that'll change the answer significantly.

That said, for the battery side of a 100/30 the output is 30A continuous, so you're looking at minimum 6mm² flexible fine-stranded cable (not rigid singles — vibration kills connections over time, especially in a shepherd's hut on uneven ground as I've found to my cost).

For the PV input side, size to your actual array current rather than the 30A rating.

Use tinned copper if you can source it — marine-grade stuff from somewhere like BEP or Ancor handles the condensation cycles far better than plain copper in an uninsulated structure.

What's your battery bank voltage — 12V or 24V? Changes the arithmetic considerably.