By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD

“I lost three days of milk chilling when a 25-amp breaker melted because I sized it for the house, not the shed.”

Off-grid AC isn't magic. It's wiring, switches, and grounding that won't fry your fridge or set your shed on fire. Here's how to do it properly, no fluff.

Subpanels: Don't Just Wire Straight from the Inverter

Running all your AC loads straight from the inverter? You're asking for a fire. Big time.

Get a proper subpanel (like a 240V, 60A or 100A model) mounted near your main inverter. This is non-negotiable. Why?

• Prevents overloading your inverter's output
• Allows you to isolate circuits (e.g., fridge vs. AC)
• Meets Australian wiring standards (AS/NZS 3000)

Don't skimp. A cheap subpanel fails. A good one lasts 20 years. Get a Legrand 60A subpanel (about $220-$280 from Electrical Wholesalers or McMaster). Mount it on a non-combustible surface, 300mm from the inverter.

Transfer Switches: Stop Wasting Power on the Grid

Grid-tied? You need a transfer switch. Off-grid? You still need one if you ever want to use the grid as backup (e.g., during a storm). No excuses.

Use a double-pole, double-throw (DPDT) transfer switch. This physically disconnects the grid when you're off-grid. Cheap ones (under $300) are dangerous. Get a proper one.

Best option: Siemens 200A transfer switch (about $450-$550 from Electrical Wholesalers). Install it between your main breaker panel and the grid connection. No DIY on this one. Get an electrician.

Grounding: The One Thing You'll Forget (And Regret)

Grounding isn't optional. It's the difference between a safe system and a death trap. Do it right or don't do it at all.

Steps:

1. Run a 6mm² copper earth wire from your inverter's earth terminal to a 1.5m copper rod
2. Connect the subpanel's earth bar to the same rod
3. Use a 25mm² copper strap to bond the inverter frame to the earth rod

Forget the "grounding rod in the garden" myth. You need a proper earth electrode (like a 1.5m copper rod) driven into moist soil. Test it with a ground resistance tester ($150-$250 from Angus). Target: under 25 ohms.

Real Talk: What You'll Actually Spend

Here's the real cost for a basic 240V off-grid AC setup (not including inverter):

• Subpanel (60A): $250
• Transfer switch (200A): $500
• Grounding kit (rod, wire, clamp): $120
• Electrician (2 hours for install): $400-$600

Total: $1,270-$1,470. Yes, it's a cost. But it's cheaper than replacing your house after a fire.

When to Call a Professional

While many off-grid projects are achievable as DIY, certain situations require licensed professionals:

• Electrical work beyond basic 12V DC additions — requires a licensed electrician
• Structural modifications to buildings or load-bearing elements
• Gas line installation or modification
• Solar array installations above safe voltage thresholds
• Any work that affects the structural integrity of your property

Always check local regulations and obtain necessary permits before commencing work.