Inquiry regarding maximum cable cross-section 25 mmq for Orion XS 12/12-50A terminals

Been speccing out the wiring for my motorhome build and I've hit a bit of a snag with the Orion XS 12/12-50A that I'm hoping someone with hands-on experience can clarify.

The datasheet lists 25 mm² as the maximum cable cross-section for the screw terminals on the power connections. My issue is that I'm running fairly long cable runs — around 3.5 metres from the starter battery to the unit — and to keep voltage drop within sensible limits at 50A continuous, my calculations are pointing me towards 35 mm² rather than 25 mm².

A few questions:

• Has anyone managed to terminate 35 mm² into these terminals using a ferrule or by other means, or is 25 mm² genuinely a hard physical limit?
• If I'm stuck at 25 mm², would the correct approach be to run parallel 25 mm² cables on both positive and negative, effectively halving the current per conductor?
• Alternatively, is it worth positioning the Orion XS closer to the source battery to shorten the run and make 25 mm² viable on voltage drop grounds?

I'm using a Fogstar 100Ah lithium on the leisure side and want to make sure I'm not throttling the charge current through poor wiring. The Victron documentation isn't particularly explicit about whether the terminal rating is a mechanical limit or simply a recommendation.

Anyone who's installed one of these in a similar long-run scenario — what did you actually do? Parallel cables feels inelegant but might be the pragmatic solution here.

25mm² is the max the terminals will physically accept — I jammed 35mm² in mine once and spent a fun afternoon crying in my van 🔧

@RiverFinn 😂 been there mate.

25mm² is fine for 50A runs if you're keeping cable lengths sensible. Worth checking your voltage drop over the full run though — if you're going longer than a couple of metres you might want to upsize the cable and use a reducer/lug at the terminal rather than fight the connector.

I did exactly that on my van build — 35mm² cable for the main run, crimped down to a 25mm² bootlace ferrule at the Orion end. Victron's own terminals are a bit fiddly but they grip ferrules well.

Just make sure whatever crimping tool you're using is actually rated properly — cheap ones can leave you with a dodgy joint that gets warm under load.

@Liam1990 One thing worth adding: at 50A continuous you're sitting right at the practical limit for 25mm² in an enclosed run — ambient temperature and bundling derate that figure meaningfully. I'd suggest running separate 25mm² cables for input and output rather than trying to compensate elsewhere.

Also worth noting the Orion XS wants proper cable ferrules on those terminals, not bare stranded ends. Weidmüller or similar bootlace ferrules crimped properly make a real difference to contact resistance and longevity — I've measured a notable voltage drop improvement in my shepherd's hut setup after switching from bare copper. A decent ratchet crimper isn't optional here.

Finally, double-check your fusing is sized to the cable, not just the unit — 60A ANL close to the source battery is the typical recommendation for 25mm² in this application.

Great first post, @Liam1990 — this is exactly the kind of spec detail worth pinning down before you're elbow-deep in a build.

To add something not yet mentioned: if your run is on the longer side, consider whether tinned copper cable is worth the premium over plain copper. In a motorhome environment with humidity and vibration, tinned resists corrosion at the terminals noticeably better over time. Fogstar and TCS Cables both stock decent tinned flexible welding cable in 25mm² that terminates cleanly into the Orion XS lugs.

Also double-check your ferrules — bare-ended stranded cable compressed under those terminal screws can cold-flow over time and loosen. Proper crimped bootlace ferrules make a real difference to long-term connection integrity.