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Home Generator 101

December 27, 2013

generator house

With snow storms affecting much of the U.S. people have power outages on their minds. We’ve found that people have plenty of questions about generators for their home, including where they can run a generator, how big of one they need to buy and how to connect it to the house’s power supply.

Here are 10 basic generator questions people ask, and their answers.

1. How Big a Generator Should I Get?

We’re not talking physical size, but, rather, a generator’s electrical capacity. This size depends on the sum of the electrical loads you want to power simultaneously, measured in watts. First, add up all the loads you know you want to be able to run simultaneously. Then, as a precaution, figure out which electrical item in your house requires the most electricity to start its motor and add that to your total. The reason for this is that large items like air conditioners tend to use a lot of juice when they start up—two or three times what they use while they’re running. You want to make sure your generator can accommodate that extra electricity requirement; that way, larger items won’t overload the system if they start up.

Every generator has two wattage ratings: running wattage and surge wattage. Generators are rated for surge wattage because they should have some excess capacity in case the load you need is temporarily larger than what you’ve calculated. When you buy a generator, choose the size based on the running wattage and its surge wattage should automatically fall into line with what you need. If you’re worried about needing more surge wattage, buy a larger generator.

2. What Loads Should I Consider Powering with the Generator?

Here is a typical example:

First-floor bathroom

A couple of lighting circuits



Garage door opener

Well pump

Other loads to consider are a sump pump, a sewage ejector pump or a circuit into which you can plug a window air conditioner.

3. How Do I Calculate All This?

Generator manufacturers and retailers post helpful sizing worksheets or wattage calculators on their websites to help you figure it all out. GE is a good example.

4. Do I Need to Hire an Electrician to Set Up a Generator Safely?

The safest way to run a generator is to plug it into a piece of electrical equipment called a transfer switch. This is a combination switch and electrical subpanel. It’s wired directly into the house’s service panel, and the generator is plugged into it. When you throw its switch, it does two things. First, it disconnects the house from the grid outside. This prevents power from the generator from flowing outside the house, where it can injure or kill a utility worker. Second, it sends power only to house circuits that you’ve designated. That way, the generator won’t be overloaded.

Unless you’re an experienced amateur (you have previous electrical and mechanical training but lack an electrician’s license), it’s best to have a licensed electrician install a transfer switch.

5. Can’t I Just Plug My Generator into a Wall Outlet?

No. This is known as back feeding, and it’s blatantly dangerous for a variety of reasons. For instance, if someone forgets to throw the main circuit breaker to electrically isolate the house from the grid, then the generator could send electrical power beyond the house and out onto the grid. When that happens, the electricity you’re generating could injure or kill a utility worker who has come to repair the downed grid.

6. What are the Differences between a Standby Generator and a Backup Generator?

A standby generator is permanently installed apparatus, much like a compressor for a central air- conditioning system. Its engine runs on natural gas or propane. A backup generator is a small, gas-engine generator that you wheel into position outside the house and then plug into the transfer switch. Or it can be connected to electrical loads via heavy-duty extension cords.

7. If It’s Raining or Snowing Outside, Can I Put the Generator in the Garage and Run it There, as Long as the Door Stays Open?

No. Never run a generator inside a house, inside a garage, under a carport, on a porch, inside a screened porch or near an open window. Even with the garage door open, the carbon monoxide (CO) in the generator’s exhaust can sicken somebody inside the house or, in the worst case, even kill someone.

8. What Other Safety Tips Should I Keep in Mind?

Have working smoke and CO detectors in the house when using a generator.

Keep the generator at least 10 feet from the house to minimize risks from CO and also the risk of the generator’s hot muffler melting vinyl siding.

Never fuel a generator while it’s hot. Remember: “Let it cool before you fuel.”

9. Generators are loud. What Can Be Done About That?

Unfortunately, not much. More mechanically advanced generators do a better job than older ones at adjusting engine rpm to their electrical output. This reduces their running speed, which is quieter and conserves fuel. Some home tinkerers are experimenting with putting mufflers from motorcycles and ATVs on their generators. This can be done if you have the requisite metalworking skills. But be warned: In most cases it will void the generator’s warranty.

You have to do your part, too: The simplest way to reduce generator noise is to reduce the electrical load you’re imposing on it. Besides, it’s unrealistic to think you can maintain your typical lifestyle on a small gas-engine generator outside your house.

10. Does the Generator Need to Be Grounded?

Follow the instructions in the owner’s manual. If the manual calls for grounding the generator, that’s relatively easy to do. One simple way is to run a 12-gauge ground wire from the grounding terminal on the generator to a copper ground rod you’ve driven into the soil next to the generator. (The generator will have a grounding terminal symbol to help you identify the terminal’s location.)

As an alternative, the manual may ask you to run a ground wire from the generator’s grounding terminal to the ground bus inside the house’s service panel. As long as you follow the instructions provided in the manual, the generator will be safely grounded.

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