Off grid 24volt growatt grounding issues

Running a Growatt SPF 3000TL LVM-24 on my narrowboat and I've been going back and forth on the earthing setup for a while now. Currently have a 24V Fogstar lithium bank with Victron MPPT handling the solar side.

The issue I'm having is around how to properly earth the Growatt's chassis given the floating nature of a boat's DC system. On land installs I understand you'd typically bond the neutral to earth at the inverter, but on a narrowboat this gets complicated — you've got hull bonding, shore power considerations, and the risk of galvanic corrosion to think about.

Specifically:

• Should the Growatt's chassis earth be bonded directly to the negative busbar, or kept separate?
• Is the neutral-earth bond inside the Growatt active when running in inverter-only mode (off-grid, no shore power)?
• Anyone had issues with RCDs tripping due to floating neutral when powering appliances that have their own earth leakage?

I've read through the Growatt manual and it's about as clear as mud on this. BSS requirements add another layer to this — last thing I want is failing an examination because I've bodged the earthing.

Has anyone running a similar Growatt setup on a boat (or even a vehicle) cracked this properly? Interested in how you've approached the neutral-earth bond specifically rather than general inverter grounding advice.

@FrostySailor — narrowboat earthing is its own beast compared to static installations. The key thing with the SPF 3000TL LVM on a floating vessel is that you're dealing with a floating DC negative, not a solid earth reference. Growatt's neutral-earth bonding on the AC output can cause grief when you're also connected to shore power, as you'll end up with a ground loop through the hull.

What I'd recommend:

• Use a galvanic isolator (BS EN 60309 compliant) on your shore line
• Keep your DC negative unbonded from the hull — measure continuity to confirm
• Your Victron MPPT chassis earth should go to a single star point, not the hull directly

Is your Fogstar bank using a separate BMS earth? That's often where things go sideways on boats. What does your current bonding diagram look like?

@FrostySailor been down this exact rabbit hole on my own boat — the SPF 3000TL's floating neutral will have you questioning your life choices at 2am whilst moored near a marina full of nosy BSS inspectors.

Floating neutral on a boat hull = a bad day waiting to happen, trust me on that one — bond your neutral to earth once at the inverter, nowhere else, or you'll be chasing phantom faults till the cows come home.

Also worth checking your BSS (Boat Safety Scheme) requirements before an examiner catches you out; they're not as clued-up on lithium installs as they should be but they'll still fail you on dodgy earthing.

On the Fogstar bank specifically — make sure your BMS earth reference plays nicely with the Growatt's internal topology, because some of those Growatts get a bit confused about where ground actually is when the neutral floats.

@VoltageViking is right to question it — I spent three weeks on mine before it stopped nuisance-tripping my RCD.

Interesting thread — coming at this from a tiny house angle rather than a boat, but the SPF 3000TL grounding question is something I've wrestled with too.

@DodgySocket makes a solid point about bonding neutral to earth once. What I'm curious about is where exactly others are doing that bond in their Growatt setups — at the inverter chassis, at a dedicated earth bar, or at the consumer unit?

Also, with a Fogstar lithium bank specifically, does the BMS earthing factor into this at all? My own setup has the BMS negative connected to a common earth bar and I'm never entirely confident I've got it right.

Has anyone used a proper isolation transformer to sidestep the floating neutral issue altogether on marine installs? Seems like it might be the cleaner solution but adds cost and complexity.

@FrostySailor the Growatt's "EPS" mode grounding behaviour changes depending on whether it detects grid presence, so your bonding point needs to account for that switchover or you'll be chasing phantom RCD trips at 2am in a Norfolk Broad with no phone signal.