Earth for Orion XS in T5 camper

Just gone through this exact rabbit hole myself with the garden office van build — ended up fitting an Orion XS 12/12-30 and honestly it's transformed how quickly the leisure battery tops up on a run.

One thing that caught me out though: earthing. The T5 chassis earth situation is a bit of a faff compared to what the wiring diagrams make it look like.

Quick questions for anyone who's done this:

• Did you run a dedicated earth cable from the Orion XS directly back to the battery negative, or did you just chassis earth it at a nearby bolt?
• I've seen some folk say the T5 chassis isn't the cleanest earth path and you can get weird behaviour from the charger if it's not done properly — anyone actually experienced this?
• My starter battery is under the driver's seat — is it worth running the earth all the way back there, or is a solid chassis point nearby good enough?

For context I'm running a 100Ah Fogstar Drift as the leisure battery, so the Orion XS seemed like the obvious Victron pairing. The B2B over a split charge relay is a no-brainer once you're on lithium — the relay would just never let the alternator do its job properly.

Just want to make sure I'm not creating a gremlins situation by cutting corners on the earthing before I button everything up. 🔌

Anyone with T5/T6 specific experience, especially on the dedicated vs chassis earth debate — what did you actually do and has it caused any issues?

Worth noting the XS variant is non-isolated so your earth path matters a lot more than people realise. If both batteries share a common chassis earth (which they will in a T5), you technically don't need a dedicated negative cable between them — the chassis does the work.

That said, I ran a direct negative on my shepherd's hut build using a proper tinned cable between the two battery negatives anyway. Keeps volt drop predictable and avoids chasing weird gremlins through aged body joints later.

@VoltPaddy what gauge cable are you running on the positive? People often overspec that and completely ignore that the negative path needs to match it.

@ExPostie is right to flag the earth path — with a non-isolated unit the Orion XS needs both batteries sharing a common chassis earth to function correctly.

Quick checklist worth running through:

• Confirm your leisure battery negative goes back to the same chassis point as your starter battery negative
• Measure the voltage drop across that earth path under load — anything above ~0.2V suggests a poor connection
• The XS input and output negatives on the unit itself — are you running those to chassis locally, or back to the battery?

I've been planning an Orion XS install for my static caravan's EV charging setup (via a 200Ah Fogstar Drift) and the earth topology is the bit I keep second-guessing. What chassis point did you end up using, @VoltPaddy — bodywork stud or direct to engine block?

@ExPostie and @BlownFuse have covered the earth side nicely — just want to add that on my narrowboat I ran the Orion XS earth directly to the negative busbar rather than chasing back to the starter battery, and it's been rock solid ever since. T5 chassis earth points can be a bit grim with corrosion too, so give wherever you're bolting a proper clean back to bare metal or you'll be scratching your head wondering why Victron Connect is showing weird voltage drops.

@WonkyHermit narrowboat gang represent — mine's been bolted to a bulkhead on a 58-footer for two seasons and the only drama was me forgetting the Bluetooth dongle existed until spring.