Must the MPPT 100/30 be Isolated from RV Chassis Ground?

Had a similar head-scratcher on my van conversion build last year.

When I was wiring up my Victron MPPT 100/30, I noticed there was continuity between the PV negative and the vehicle chassis. Spent an afternoon convinced I'd done something wrong before I actually sat down with the manual properly.

Worth clarifying for anyone else confused by this:

• The Victron 100/30 is not a galvanically isolated unit — PV negative and battery negative are connected internally
• If your battery negative is bonded to chassis (common in 12V vehicle setups), then PV negative will show continuity to chassis ground — that's expected, not a fault
• Where you'd have a problem is if PV positive showed continuity to chassis, which would suggest a wiring error or a short somewhere in the array

So the question isn't really "should the MPPT be isolated from chassis ground" — it's more about which terminal is making contact and why.

Has anyone here actually opted for a fully floating system in their RV or van setup? I've seen some arguments for keeping PV completely isolated from chassis to reduce corrosion risk on aluminium frames, particularly with larger arrays. Fogstar and some other UK suppliers seem to recommend it for certain lithium setups but I've never seen a definitive answer.

Curious whether anyone's had an actual fault traced back to this, or whether it's mostly theoretical concern. Also wondering if it differs at all between split-charge setups versus dedicated solar-only systems.

Would appreciate hearing from anyone who's dug into this properly.

@OddJobBob22 did you actually measure whether that continuity was causing any issue, or just flag it as a concern?

On my static caravan build I had exactly this — Victron MPPT 100/30, and the PV negative was floating relative to chassis until I accidentally created a path through the battery negative. Caused no actual problems once I understood why it was happening.

Key question: are you running a negative earthed system where battery negative is intentionally bonded to chassis? Because if so, continuity to PV negative through that bond is completely expected behaviour, not a fault.

Where it gets dodgy is if you've got two separate paths creating a ground loop — that's where you'd see issues with BMS readings or weird charge behaviour.

What does your earthing arrangement actually look like? Single bond point or multiple?

@OddJobBob22 this is giving me flashbacks to the absolute rat's nest I created on my narrowboat when I first wired up the solar — convinced myself I'd done something catastrophically wrong because of similar continuity readings, turned out I'd just fundamentally misunderstood how the Victron handles its negative rail.

Worth clarifying: is your boat/van on shore power at the same time? On the narrowboat I've got a slightly paranoid setup where everything doubles as emergency backup, and mixing shore ground with the chassis ground through the MPPT negative created a lovely little ground loop that made my BMV-712 read absolute nonsense for about three weeks before I cottoned on.

@LisaStewart71 raises a fair point — continuity existing doesn't automatically mean current is flowing where it shouldn't be. Have you actually measured any leakage current, @OddJobBob22?

@OddJobBob22 worth knowing the MPPT 100/30 uses a common negative design — PV negative and battery negative are internally connected, so that continuity you measured is by design, not a fault.

The real question is whether your chassis ground is then creating an unintended parallel path. In a van that's usually fine if you've got a proper single-point grounding scheme, but it can cause headaches with some BMS units that monitor current on the negative rail.

I had something similar on my garden office build — ended up with weird BMS trips until I realised my Fogstar battery's BMS was seeing stray current from exactly this kind of loop.

Check your grounding topology first before assuming something's broken. Victron's own wiring docs cover this — worth a read before pulling anything apart.

@QuietTrekker has nailed the key point — common negative is the crux of it.

Worth adding: in a negative-earthed vehicle (virtually all modern vans), that continuity is by design and completely fine. Your PV negative, battery negative, and chassis are all intentionally bonded together.

Where it gets problematic is if you're running a floating or positive-earth system, or if you've got a ground fault somewhere creating an unintended path — that's a different beast entirely.

On my own narrowboat build I use a Victron SmartSolar 100/30 with fully floating DC negative (BSS recommends isolation on boats), so I do keep PV negative isolated from hull. Van conversions are a different world — chassis ground is your friend there, not your enemy.

If you're seeing continuity and you're on a standard negative-earth van, measure the voltage across that path. If it's near zero, you're sorted.