We get this call more often than you’d think: “My generator just won’t stop running, and it’s not even about the battery being low.” If you’ve got an off-grid solar setup — solar, lithium battery, and a backup generator working together — and you’ve noticed it acting up since some recent electrical work was done, here’s a fault we see often, and why a general electrician without solar-specific experience can easily miss it.

The symptom

The generator keeps getting a start signal, even when the battery state of charge is healthy. It looks like a battery or inverter fault, so people naturally assume that’s where the problem lives. But on inspection, the battery and inverter are both working exactly as designed.

The real cause: a double neutral-earth bond

In a properly designed off-grid system, there’s supposed to be exactly one neutral-earth bond (NEB) point at any given time. Your inverter has its own internal switched NEB, and your generator has a factory NEB built in. If a permanent NEB link gets added at the distribution board after the system was installed — sometimes during unrelated electrical work, with no one realising the implications for the solar/generator setup — you end up with two or three active bonding points fighting each other.

That creates circulating earth fault currents between the bonding points. The system reads this as a fault condition and triggers a generator start signal, completely unrelated to actual battery charge. It can look intermittent, confusing, and expensive to chase if you don’t know exactly what you’re looking for.

Why this gets missed

SANS 10142-1 requires a single, active NEB point in a switched arrangement — not multiple permanent ones. Most general electrical work doesn’t touch this, so it’s an easy thing to overlook if you’re not specifically thinking about how your DB interacts with an inverter and generator. The fix isn’t to remove earthing — that would be unsafe — it’s to correct which bond is active and when.

The fix

Replace the permanent DB link with a switched NE bonding contactor controlled by the inverter, so it only engages in island mode (when the system is running off-grid). That restores a single active bonding point at any given time, stops the false fault signals, and keeps the installation compliant.

The takeaway

Off-grid hybrid systems sit at the intersection of electrical compliance, inverter logic, and generator behaviour — three things that don’t always get considered together. If your generator’s running for no obvious reason, the answer isn’t always a battery or inverter replacement; sometimes it’s a five-minute look at the earthing arrangement that gets missed by anyone who isn’t specifically looking for it.