Key takeaways
- A standby generator is permanent and automatic. A portable one is manual and has to be run outdoors.
- A transfer switch or interlock is required for either type to power house wiring safely.
- Backfeeding through an outlet can kill utility workers and damage the generator.
- Size by listing what you need to run, adding the running loads, and allowing for motor starting surges.
- Installation of the switch, the wiring and the gas line is work for licensed professionals.
How the two types differ
A portable generator is a gasoline engine you wheel out and start when the power fails. It is the lower-cost option, and many homeowners keep one in the garage or shed. Someone has to be home to set it up, keep it fueled, and shut it down.
A standby generator sits on a pad outside the house and is wired permanently into the electrical system. It runs on natural gas or propane, starts itself within seconds of an outage, and shuts down when utility power comes back. It also works when you are away, which matters for sump pumps and refrigerators during a storm that lasts days.
The tradeoffs are cost, installation and space. A standby unit needs a permit, a gas connection, a level pad and clearance from windows and doors. A portable needs fuel storage and a safe place to run. Outages in Southwest Ohio often follow severe storms, wind and ice, so many people think first about the sump pump, the furnace blower and the refrigerator.
Transfer switches and interlocks
Neither type should be connected to a house without a transfer switch or interlock. These devices keep the house on one power source at a time, either the utility or the generator.
A standby generator uses an automatic transfer switch. It senses the outage, starts the generator, moves the load over, and reverses the process when power returns. A portable generator can use a manual transfer switch, which is a small subpanel holding the circuits you have chosen to back up. Another option is an interlock kit on the main panel, which blocks the main breaker and the generator breaker from being on together. It is paired with a weather-rated inlet on the outside of the house, so you plug the generator in with a proper cord.
Choosing which circuits to back up is part of the planning. Common picks are the refrigerator, the sump pump, the furnace blower, a few lights, and some outlets for phones and a router. These systems have to match the service rating and meet code, so they are electrician work. If you want advice on equipment, see generator installation.
The danger of backfeeding
Backfeeding means pushing generator power into the house wiring in a way that lets it flow back out to the utility lines. The usual cause is a homemade cord with a male plug on both ends, plugged into a dryer or wall outlet to power the house.
This can kill. A line worker repairing what they think is a dead line can be shocked by power coming back from your house through the transformer. It can also start a fire in your wiring, because the circuits were never meant to be fed that way, and it can wreck the generator when utility power returns.
There is no safe version of this shortcut. If you want to power house circuits, the answer is a transfer switch or an interlock, installed and inspected. If you cannot do that, run appliances directly from the generator with heavy-duty outdoor-rated extension cords, and keep the generator outside and away from the house.
Sizing in general terms
Sizing starts with a list. Write down what you want to run during an outage, then find the running wattage of each item on its label or in the manual. Add them up.
Then allow for starting surges. Motors, such as a sump pump, refrigerator compressor, furnace blower, well pump or air conditioner, draw much more power for a moment when they start than when they run. The generator has to handle the largest starting surge on top of the other loads already running. Central air conditioning, an electric range, an electric water heater and an electric dryer are large loads, and many households choose not to back them up.
A smaller generator serving selected circuits is common and practical. A larger standby unit can serve more of the house, but its size should come from a proper load calculation. Your electrician can also tell you whether your gas supply and meter can feed a standby unit, since a licensed gas fitter may need to size the line. Generator power can also be rough on electronics, so consider surge protection for sensitive equipment.
Placement, fuel and upkeep
A standby generator has to sit at the distances from windows, doors, vents and property lines that the code and the manufacturer specify. It should be on a firm, level pad where water does not pool, with room around it for service.
A portable generator runs outdoors only, in the open, well away from the house. Do not run it under a porch, in a garage or near a window. Keep it dry, and let it cool before refueling. Store gasoline in approved containers away from living space, and know that gasoline left for months can go stale and cause hard starting.
Both types need upkeep. Standby units usually run a short test cycle on a schedule, and they need periodic service of the oil, filters and battery. Portables should be started and run under load now and then so you find problems before an outage does. To plan a setup for your house, you can contact us.
Frequently asked questions
Can I run a portable generator in my garage with the door open?
No. Carbon monoxide builds up quickly and can seep into the house, even with the door open. Run it outdoors in the open, well away from windows, doors and vents.
Do I need a transfer switch for a portable generator?
If you only plug appliances directly into the generator, no. If you want to power any of your house circuits from it, yes, you need a transfer switch or an interlock with an inlet, installed by an electrician.
Is a standby generator worth it compared with a portable?
It depends on how often you lose power, how long outages last, and whether you rely on a sump pump, medical equipment or a home office. If you are often away or cannot manage a portable in bad weather, a standby unit may be the better fit.
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