What Happens If Power Comes On While the Generator Is Running?
If power comes on while the generator is running, what happens depends on the hookup. Appliances plugged into a generator won't notice. A generator backfeeding house wiring can be badly damaged when the grid returns.
What Happens When Power Returns, by Setup
People run a generator in a blackout one of three ways. Each behaves differently the moment the grid comes back.
Appliances Plugged Straight Into the Generator
Nothing happens. The fridge and lights on extension leads stay on generator power, and the house power points come back to life with nothing plugged into them.
The Electrical Safety Office explains why this setup is safe. A portable generator connected directly to an appliance through its plug and supply cord has no path back to the electrical switchboard, so the grid and the generator never meet.
The only catch is you won't know the power's back unless you check. More on that below.
Electrician-Installed Backup Connections
Also a non-event, if the job was done properly. A licensed electrician fits a changeover switch that, in the Electrical Safety Office's words, allows power to be fed from only one source, the generator or the grid, at one time.
With a manual switch, the house stays on the generator until you move the switch back. One Grey Nomads forum member with an electrician-installed setup put it simply: there's no power to their power points and lights when the mains comes back on until they change the switch.
Automatic systems make the swap for you. The Westinghouse iGen4500AS has a two-wire start terminal, so a transfer switch or an off-grid solar controller can start it, run it and stop it without you there. That switch is a separate purchase and a licensed electrician's job. The options are covered in how to connect a generator to your house in Australia.
A Generator Backfeeding Through a Power Point
This is the one that goes wrong. If a generator is feeding the house through a power point or a makeshift lead, the generator and the grid end up on the same wires when the power returns.
Three Queensland and NSW authorities describe the result the same way. The Electrical Safety Office says that if power is restored while your generator is backfeeding, it may severely damage the generator. Energex says it could damage or destroy the generator when mains power is restored, and Ausgrid adds that backfeeding can damage household appliances as well.
The damage at restoration is the smaller problem. Before the power came back, that generator could have energised lines crews believed were switched off, which Ausgrid calls a serious safety hazard. Our article on plugging a generator into an outlet covers why it's illegal.
How to Tell When the Power Is Back
Plug-In Setups
Leave one house light switched on so you notice when it comes back. Check whether the neighbours' lights or the street lights are on.
Energy Safe Victoria points out that restoring power is the job of your electricity supply company, so they're the ones to contact about when your area is expected back on.
Electrician-Installed Setups
If the house is cut off from the grid while it runs on the generator, your lights won't tell you anything. Another Grey Nomads member, whose electrician fitted a three-way switch that shuts off the solar and the mains, said they check with the neighbours to see if the power's back.
Ask your electrician what your setup shows when mains power returns, and write it on a card next to the switch.
Switching Back to Mains Safely
Plug-In Setups
Switch the appliances off, unplug them from the generator leads and plug them back into the house power points. Then shut the generator down the way its manual says. Energex says to let it cool before refuelling.
Energy Safe Victoria's steps for turning power back on after an outage are worth following at the same time. Unplug or turn off appliances first, then press and hold the safety switch's test button. If the RCD trips straight away, reset it and start switching equipment back on. If it fails the test, turn it off and get a licensed electrician to replace it.
Electrician-Installed Setups
Follow the switching order your electrician gave you when they installed it, and don't improvise. If the house has storm or flood damage, leave it alone. Energex says not to turn on the isolating switch if your home has been damaged.
The short version: plugged-in appliances and a properly installed switch don't care when the power comes back. A generator backfeeding through a power point does, and so does anyone working on the lines.
If you're sizing a generator for blackouts, can I use a generator to power my house is the place to start, and the generator finder narrows it down. Or call us on 03 7056 6732, or SMS 0476 330 590.
