Anyone else running a Victron Orion-Tr Smart in non-isolated mode? Getting confused about grounding

I've been fitting a Victron Orion-Tr Smart 12/12-30 in my Transit-based camper build and I've gone back and forth about whether to use it in isolated or non-isolated mode about five times now. I've settled on non-isolated since my leisure and starter batteries share a common chassis ground, but I'm now second-guessing whether I've got the grounding sorted properly on the output side.

The way I've wired it: starter battery positive to Orion input, chassis ground to Orion input negative, Orion output positive to leisure battery positive, and the output negative tied back to the same chassis ground point rather than running a separate negative back to the starter battery. Victron's own docs are a bit vague on this and I've seen wildly different opinions on the forums and YouTube.

My concern is whether sharing that ground point introduces any noise or charging issues in practice. The unit seems to be working fine — it's pulling around 25–27A and topping the 100Ah lithium up nicely — but I want to make sure I'm not storing up a problem. Has anyone done any voltage drop testing on the ground path, or is there a cleaner way to run the negatives that people have found makes a difference?

@SophieClark the grounding thing tripped me up too when I fitted mine in the static van. Key thing in non-isolated mode — your chassis grounds need to be properly bonded together already, otherwise you're asking for trouble.

If your Transit body is the negative return for both banks, you're probably fine. But if there's any doubt, just go isolated and stop overthinking it. The isolated version removes the headache entirely.

I ran non-isolated for a bit and ended up switching just for peace of mind. Tiny price difference really.

Victron's own wiring unlimited PDF covers this pretty well — worth downloading if you haven't already.

Got one on my narrowboat and went through exactly the same headache.

If your Transit chassis and your habitation battery share a common negative — which they almost certainly do if you've run a negative cable between them — you must use non-isolated mode. Using isolated mode with a shared negative apparently creates a ground loop that can fry the unit.

Non-isolated is simpler anyway. Just make sure both negatives are genuinely bonded, not relying on some flimsy chassis connection.

What's actually confusing you — the wiring diagram or the Victron Connect settings? Because the app settings for non-isolated mode are a separate issue from the physical grounding, and plenty of people mix the two up.

What does your current negative setup actually look like?

Ran mine non-isolated in the motorhome for two years. The bit that actually caught me out wasn't the grounding itself — it was forgetting that in non-isolated mode the input and output negatives are internally connected, so if you've got a separate leisure earth to chassis somewhere downstream, you've effectively created a loop.

Worth grabbing a cheap multimeter before you button everything up and confirming there's no voltage difference between your van chassis and your leisure battery negative. If there isn't, non-isolated is fine and saves you a few quid.

@BurnWalker raises a fair point about shared chassis — narrowboats are a different beast entirely though, I'd always go isolated on water.

Victron's own wiring diagram for non-isolated is actually clearer than most of the forum advice floating around. Start there, then question it.

@SophieClark the bit everyone forgets is that in non-isolated mode the Orion is essentially just a fancy DC voltage converter with a shared negative — so if your Transit already uses chassis earth for the starter battery (it does, it's a Transit), your leisure battery negative must go to the same chassis point, not floating off to some random bolt near the wheel arch like I definitely didn't do on my van build. 🙃

One pedantic but genuinely important detail: Victron's own wiring diagram shows the input and output negatives linked internally in non-isolated mode, so a separate negative cable between chassis and leisure battery isn't optional, it's load-bearing to the whole setup working correctly.

@SophieClark worth noting from my shepherd's hut setup (obviously static, different context) — when I was researching the Orion-Tr for a similar dual-battery situation, the Victron docs actually have a fairly clear decision flowchart buried in the manual. Non-isolated is fine if both battery negatives share a common ground already. The danger is creating a ground loop if they're separately earthed.

On a Transit specifically, your habitation battery negative should run back to the chassis rather than connecting directly to the vehicle battery negative — that keeps everything referenced to the same point and non-isolated works cleanly.

The Victron Connect app also flags it during setup which is handy. If there's any doubt at all though, isolated just removes the headache entirely for the sake of a few extra quid on the purchase price.