Ground fault on my solar system — help!

Ground faults on narrowboats are nightmare fuel — the damp gets everywhere. Few things worth checking beyond the roof penetrations:

Combiner box — if you've got one, check the glands and terminals inside. Salt spray + moisture = corrosion you won't spot immediately. I had a dodgy connection in mine last year that took forever to find.

DC isolator — sometimes the issue is actually between the array and your charge controller, not the array itself. Try isolating sections of your string and testing each run separately with a multimeter.

Cable routing — any cables running through bilge areas or near standing water? Even "sealed" conduit degrades over time on boats.

What's your charge controller showing? Victron gear tends to give better fault diagnostics than some of the cheaper units. If it's just throwing a generic ground fault alarm, that's less helpful than specific DC-to-ground readings.

Also worth asking — how old's the system? Older Renogy stuff can be a bit flaky with moisture intrusion from what I've seen.

Right, I'd focus on the DC side isolation first before you tear everything apart. Grab a multimeter set to resistance and disconnect your array at the combiner box — measure from each string to ground (the boat's hull works). Anything under 100kΩ needs investigating.

The reason I mention this: on my shepherds hut setup I chased a phantom fault for a week before realising moisture had worked into the junction boxes themselves, not just the glands. Pop yours open in a dry spell and inspect for condensation or corrosion on the terminals.

One thing the others haven't mentioned — if you're running an older Renogy MPPT controller, some firmware versions had sensitivity issues with damp environments triggering false faults. What model controller have you got? Worth checking Renogy's site for updates.

Also, what's your actual fault reading showing? Ground fault current, or just the indicator light? If it's the latter, sometimes it's just the isolation monitoring relay being finicky rather than actual leakage. Check whether disconnecting the monitoring circuit itself clears it — doesn't fix the root cause but confirms what you're chasing.

Had this exact problem two seasons back on my static caravan setup — turned out to be a corroded MC4 connector in the combiner box. Moisture had crept in despite the IP65 rating. Worth checking your connections for green oxidation before you start pulling cables. A Fluke multimeter and some dielectric grease saved me a fortune in replacement kit.

Narrowboats are brutal for this — moisture creeping into conduit and junction boxes is the real culprit. Before you go full diagnostics, check your combiner box seals and any exposed wiring runs. I once found water pooling inside my Victron SmartSolar after heavy rain. The damp gets in through the tiniest gaps. Inspect weatherproofing first, saves hours of troubleshooting.

@RobBennett93 had similar grief with my garden office setup last year. Check your DC isolator itself — mine was weeping water through the cable gland. Victron ones are solid but cheap isolators can corrode internally. Worth inspecting before the expensive diagnostics. Narrowboats are definitely moisture nightmares though, @LiFePO4Nerd's spot on there.