Schematic review unsure if grounding method is correct for DC only system

Been through exactly this head-scratching moment when I wired up my shepherd's hut last spring.

DC-only system, completely standalone — no grid, no house connection, nothing. Just a couple of 200W Renogy panels on the roof, a Victron SmartSolar MPPT, and a Fogstar Drift 100Ah lithium keeping the lights and a 12V fan ticking over nicely.

The bit that had me going in circles was earthing. I'd knocked in a single earth rod near the panel mounting frame, bonded the frame to it, but then wasn't sure whether the negative busbar inside should also connect to that same rod, or stay completely floating.

After a fair bit of reading — including some genuinely contradictory advice on various forums — I ended up bonding the negative busbar to the earth rod as a single point earth. The reasoning being that in a fully isolated DC system, a floating negative is fine in theory, but one single earth point gives you fault protection without creating earth loops.

What I'm still not 100% confident about:

• Whether the chassis of the MPPT itself should be separately bonded or just rely on being mounted near the earthed busbar
• If the negative of the battery should connect to that earth point or stay isolated from it
• Whether a single rod is even adequate given I'm on clay soil up here

Has anyone else gone through this for a small standalone hut or shed setup? Would love to see how others have drawn their schematics — even a rough diagram would help. There's surprisingly little guidance that's specific to the UK for small off-grid DC systems that aren't trying to meet Part P.

Hey @OllieRoss74, sounds like a familiar rabbit hole! For a DC-only standalone system you'll want to earth your negative busbar to a proper earth rod driven into the ground nearby — single point earthing is the key thing to get right. Avoid earthing at multiple points or you'll invite ground loops which can cause all sorts of grief with readings and potentially damage sensitive kit.

Make sure your earth rod connection is solid and the conductor's adequately sized — 6mm² copper is generally the minimum I'd go with for a small system like yours. Also worth checking your RCD/fuse protection is all on the positive side.

If you can post your schematic that'd help massively — sometimes it's easier to spot issues visually than describing it. What gauge cable are you running between your panels and battery bank?

@Nobby78 has covered negative earthing but let me add some precision here — in a DC-only standalone system the distinction between earthing and bonding matters enormously and gets confused constantly.

Your negative bus earthing is correct, but you also need:

• Single earth point only — multiple earth connections create ground loops
• Earth rod to actual ground (BS 7671 compliant, min 1.2m depth for UK soil)
• All metalwork bonded to that same earth point — frame, enclosure, everything conductive

Post your actual schematic. "Grounding method unsure" tells us nothing without seeing where you've connected what.

I ran into this exact situation wiring my shepherds hut — had two earth paths accidentally and was getting phantom voltage readings on my Victron SmartShunt that made no sense until I traced it. One earth point solved it immediately.

@OllieRoss74 the bit everyone skips: your earth rod resistance matters — BS 7671 wants under 200Ω but practically for fault protection you want as low as you can get, so drive that rod deep or use multiple rods bonded together if your Welsh/Scottish soil is rocky and dry.

Also worth noting — bond your battery negative to earth at one point only, typically at the battery itself; multiple earth points in a DC system create lovely little corrosion-accelerating galvanic loops that'll quietly murder your terminals over winter. 🪦

Victron's SmartShunt goes between battery negative and that single earth/chassis bond point, keep it tidy. If you've got a Fogstar Drift LiFePO₄ with a built-in BMS, check whether it has any internal negative switching before finalising your earth path — some do, some don't, and it absolutely matters.

Really useful thread this — I've been wrestling with something similar on my narrowboat setup where I thought I had it sorted but kept second-guessing myself.

Quick question for @OldSailor — when you're testing that earth rod resistance, what are you actually using to measure it? I borrowed a mate's clamp meter but wasn't sure if that gives a reliable reading or whether you need a proper earth loop tester. On the boat I've got the added complication of being in water obviously, which I imagine affects things?

Also for a floating system like @OllieRoss74's shepherd's hut — does the single point negative-to-earth rule still apply the same way if there's literally zero AC anywhere in the system? Victron's documentation seems to suggest yes but I want to make sure I'm not misreading it.