Why backfeeding a generator is dangerous, and what to use instead

What backfeeding means

Backfeeding is when generator power flows into your house wiring without anything stopping it from also flowing out to the utility. The classic example is a double-ended cord, sometimes called a suicide cord, plugged from a generator into a dryer receptacle or a wall outlet.

It seems clever during an outage. It is one of the most dangerous things a homeowner can do with electricity.

Why it is so dangerous

• Lineworkers. Your generator's 120/240 V goes back out the service drop to the transformer, which works in both directions. On the far side it can appear at thousands of volts on a line crews believe is dead.
• Your neighbours. Homes on the same transformer can end up connected to your generator.
• Your generator and house. When the grid comes back, utility power slams into a running generator. That can wreck the generator, start a fire, or damage the panel.
• Exposed prongs. A male-to-male cord has live pins on the loose end once the generator is running.
• Overloads. A single outlet circuit was never meant to carry a generator's full output, and the breaker may not protect the cord.

Lineworkers do test and ground lines before working on them, but they should never have to rely on that alone. A single improperly connected generator on a street can turn a routine repair into an emergency, which is why utilities and safety authorities treat backfeeding so seriously.

The fix: transfer equipment

The Canadian Electrical Code requires that an alternate power source like a generator be connected through transfer equipment that prevents it from being tied to the utility supply. In plain terms, the house can be connected to the grid or to the generator, never both at once.

There are three common ways a licensed (journeyperson) electrician does this:

• Listed panel interlock. A sliding plate on the panel cover lets you turn the generator breaker on only when the main breaker is off. It must be a kit listed for your exact panel model.
• Manual transfer switch. A separate box next to the panel with a selector for each chosen circuit: line, off or generator.
• Automatic transfer switch (ATS). Used with standby generators. It senses an outage, starts the generator and switches over by itself.

The inlet box and cord

For a portable generator, the other half of the system is a power inlet mounted on an outside wall. It has recessed male pins so nothing is ever exposed. A properly rated generator cord runs from the generator's twist-lock receptacle to the inlet.

Keep the generator outdoors, away from the house, and run the cord to the inlet. Never pass the cord through a window or a door left ajar, which lets exhaust in.

What you can safely do yourself

Operating an installed system is homeowner territory. Installing it is not. Once the equipment is in and inspected, a typical changeover looks like this:

1. Set the generator outdoors in its usual spot and check fuel and oil.
2. Connect the cord to the generator and then to the inlet.
3. Start the generator and let it run for a minute.
4. At the panel, switch the main breaker off, slide the interlock, and turn on the generator breaker (or move your transfer switch selectors to generator).
5. Turn on the circuits you need, a few at a time, starting with the furnace and fridge.

When the grid returns, reverse the order: loads off, generator breaker off, main back on, then shut the generator down. Your electrician will walk you through your specific equipment.

Permits and getting it done

Adding an inlet, interlock or transfer switch is electrical work that needs a permit under the Alberta Safety Codes Act. In Edmonton the City issues electrical permits; elsewhere it is your municipality or an accredited agency. An inspection confirms the equipment is listed and installed correctly.

Some older panels have no listed interlock available, or no space for a generator breaker. In that case a separate transfer switch or a panel replacement may be the cleaner path. If you are still choosing a generator, see standby vs portable generators.

Common questions