Compare a generator transfer switch, interlock kit and extension cords, and why backfeeding is deadly for line workers. Hire a licensed electrician.
- Extension cords suit small loads; a transfer switch or interlock suits hardwired circuits and long outages.
- Both switches and interlock kits must be installed by a licensed electrician, often with a permit.
- Never backfeed through a wall outlet: it can electrocute line workers and start fires.
Once you own a generator, the next question is how to connect it to your appliances. Extension cords are the simplest. A transfer switch or interlock kit lets you power hardwired circuits such as a furnace or well pump. Both can be safe, but one common shortcut is deadly: plugging the generator into a wall outlet.
Option 1: Extension cords
With cords, you run the generator outdoors and feed individual appliances through heavy-duty outdoor-rated extension cords. This needs no wiring changes and no permit. It works well for a fridge, a few lights, a phone charger and a router.
- Pros: Low cost, no electrician, easy to set up and take down.
- Cons: Cords run through windows or doors, which can let in rain, cold and exhaust if poorly placed. You cannot power hardwired items such as a furnace, and each appliance needs its own cord.
- Tips: Use cords rated for outdoor use and the wattage of the load, keep them short, check for damage, and never run them under rugs or through pinched doorways.
Option 2: Transfer switch
A transfer switch is a device wired into your electrical panel that moves selected circuits from the utility to the generator. It physically prevents the two sources from being connected at once. A power inlet box on the outside wall gives you a place to plug the generator in with a single, proper cord.
- Pros: Safe, convenient, powers hardwired items like furnaces, well pumps and sump pumps, and no cords through windows.
- Cons: Higher cost than cords, and it needs installation by a licensed electrician. Usually requires a permit and inspection.
Some transfer switches power a handful of chosen circuits. Others handle the whole panel. Your electrician can tell you which suits your generator size and home. Make sure the switch is rated for your generator's output, and that the generator's plug type matches the inlet.
Option 3: Interlock kit
An interlock kit is a mechanical plate that sits on your main panel and prevents the main breaker and the generator breaker from being on at the same time. It is often cheaper than a full transfer switch, but it is still a panel modification. It must be installed by a licensed electrician, must be approved for your panel model, and in many places needs a permit. Rules differ across Canada and the US, so ask your local authority or electrician what applies.
Why backfeeding kills
Backfeeding means plugging a generator into a wall outlet using a cord with a male plug on both ends, hoping to power the house through its wiring. Do not do this. When your home is connected to the grid, power can travel backwards through the service transformer and raise the voltage on lines that crews believe are dead. Linemen working to restore power can be electrocuted.
Backfeeding can also overload household wiring and cause a fire, and it can damage the generator when utility power returns. In many places it is illegal. Even if you think your neighbourhood is fully dark, do not take the chance.
What to ask an electrician
- Which circuits can I power, and what is the total watt load on my generator?
- Do you recommend a transfer switch or an interlock for my panel?
- Is a permit and inspection needed, and will you handle it?
- Where should the inlet box go so the generator sits at a safe distance from windows and doors?
- What size cord and plug type do I need?
- Does my utility require notification or a particular type of switch?
Which should you choose?
If you only need a fridge, a few lights and device charging for short outages, cords are usually enough. If you want to run a furnace, well pump or large parts of the house, or if you expect long outages, a transfer switch is worth discussing with an electrician. If you prefer to avoid fuel and exhaust altogether, a battery-based option may be simpler, see solar generator vs gas generator and how to keep a furnace running in an outage.
To compare battery options, visit our power stations hub.
Quick answers
Is an interlock kit as safe as a transfer switch?
When correctly installed and approved for your panel by a licensed electrician, both are designed to stop the grid and generator from being connected together. Ask your electrician which suits your home.
Do I need a permit for a transfer switch?
Often yes, and an inspection may be required. Rules vary by location, so ask your local authority or electrician.