What is a changeover switch or ATS in a solar backup system?

Answer first: A changeover switch (manual or automatic) chooses which source feeds a circuit — municipal/Eskom grid, hybrid inverter backup, or generator — without back-feeding the utility. An ATS (automatic transfer switch) does that change without you standing at the board when load shedding hits. Correct interlocking protects municipal workers and your equipment; DIY “double feeds” are dangerous and illegal.

Why this shows up on SA hybrid quotes

Most modern hybrid inverters already island the backup (essential) circuits when the grid drops — anti-islanding and internal transfer are part of a type-tested NRS 097 design. Extra changeover or ATS hardware appears when you add a generator, a second sub-board, a whole-house vs essential-loads split that the inverter cannot manage alone, or an older UPS/inverter that was never designed as a hybrid. If the quote just says “ATS” with no sketch, ask what sources it is switching between.

Essential loads vs whole-house

Many SA homes put lights, fridge, Wi-Fi, gate motor and a few plugs on an essential backup board sized to the inverter’s continuous rating, and leave geysers, ovens and pool pumps on non-essential circuits that die with the grid. That choice is about battery kWh and inverter kW, not about the brand of changeover switch. See essential vs non-essential and Stage 6 battery sizing.

Generator + solar — the interlock that matters

If a standby generator can feed the same board as the hybrid or the grid, the changeover must be break-before-make (or an equivalent interlocked design) so two sources never parallel into a dead municipal line. That is a life-safety rule for line workers, not a nice-to-have. The CoC electrician owns that design under SANS 10142 — see what a CoC is. Never accept a “temporary jumper” story.

What to demand on the quote

• One-line diagram: grid → main DB → hybrid → essential DB (and generator path if any).
• Named make/model of any external ATS or changeover, with continuous amp rating.
• Whether the hybrid’s built-in transfer already covers the loads you care about — so you are not paying twice.
• Commissioning test: prove the house islands cleanly when the main breaker is opened (safely, by the electrician).

Load shedding reality check

Panels alone do not keep lights on when the grid fails — anti-islanding opens the inverter (does solar work in shedding?). Battery + hybrid (or generator with proper transfer) does. An ATS that starts a diesel plant after 10 seconds of darkness is a lifestyle choice; many households prefer a quiet LiFePO₄ pack for Stage 2–4 evenings and only keep a generator for multi-day outages.

SA caveats

Municipal SSEG rules care about the grid interface (NRS 097 inverter behaviour), not about your generator brand — but illegal back-feed can get you disconnected and create liability. Insurance and bond surveys increasingly ask for a current CoC after major electrical work. This page is educational — the registered electrician designs the switchgear.

Manual vs automatic — lifestyle, not status

A manual changeover is fine if someone is home and willing to walk to the board when the generator must start. An ATS earns its keep for elderly households, empty weekday houses, or sites where a generator must pick up a fridge and medical device without delay. Paying for ATS automation on a hybrid that already islands essentials cleanly is often wasted money — make the electrician justify the extra contactor.

Common failure modes homeowners should know

• Neutral / earth faults after a DIY generator plug into a socket
• ATS that transfers before the generator has stable voltage
• Backup board labelled “essential” that still includes a 3 kW geyser element
• No commissioning test — the first real Stage 6 evening is a bad time to discover a wiring error

Insurance assessors have seen these. Keep the CoC, single-line diagram and ATS manual together.

How this interacts with prepaid and TOU meters

Some prepaid and smart-meter setups behave differently when the hybrid islands. Ask your installer whether your meter type needs a specific bypass, isolation or municipal notification. TOU customers should also know whether backup loads during shedding are logged strangely on the bill — metro practices differ. Related: prepaid + solar, TOU & EV.

Quick FAQ

Does every hybrid need an external ATS? Usually no.
Can I use a changeover to illegally feed the street? Absolutely not — criminal and lethal risk.
Is a generator still worth it with LiFePO₄? Sometimes for multi-day outages; many homes skip it after a properly sized battery.

Sketch you should see on every serious quote

Insist on a one-page sketch with four labels: municipal incomer, main DB, hybrid AC terminals, essential sub-board — plus generator path if quoted. Arrows should show which contactor opens on grid loss and which source is forbidden from paralleling. If the salesperson cannot draw it, the commissioning electrician may inherit a mess. Keep that sketch with the CoC; future owners and insurance surveyors will thank you.

When comparing two installers, prefer the one who talks about sequence (detect loss → isolate grid → form island → optionally start genset) over the one who only lists brand names. Sequence errors are how neutrals float and RCDs nuisance-trip every evening stage.

Cost sanity

An external ATS for a small residential generator feed might be a modest four-figure line item; complex motorised boards run higher. If the ATS line approaches the cost of a meaningful battery upgrade, ask whether quiet LiFePO₄ capacity would buy more evenings of comfort than diesel automation. Bill maths still starts with avoided retail kWh at roughly R3.30–R4.70 — tariffs 2026 — not with switchgear theatre.

Related answers

• Essential vs non-essential loads
• Does solar work during load shedding?
• What is a CoC?
• What is NRS 097?
• Load shedding & backup guide