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<p>"The first step in choosing a generator is to determine how much electricity your household needs in an emergency."</p>

"The first step in choosing a generator is to determine how much electricity your household needs in an emergency."

Illustration by Ian Worpole

Jasper H. and Phyllis Wyman have lost power dozens of times during the 31 years they've lived in their restored farmhouse in Pittsfield, Maine. But after the ice storm of 1998, which left the Wymans without electricity for more than four days, they decided they'd had enough of living by the light of kerosene lanterns, huddled around a wood stove, with no running water because the well pump was dead. (They saved the food from their refrigerator by burying it in a snowbank.) So Jasper plunked down $7,000 for a standby generator. Sitting in the garage, its exhaust vented via a pipe through the wall, this diesel-fueled mini power plant produces enough electricity to run their lights, refrigerator, well pump, furnace, and water heater—pretty much everything the Wymans need to weather a power outage. "If we get another storm like that, it's more than adequate to do everything we need it to do," Jasper says.

The Wymans join a growing number of homeowners who are installing generators to guard against long or repeated power outages. Sales of residential units, which briefly spiked during the Y2K scare of the late 1990s, have been steadily increasing, helped in part by rolling blackouts in California, transistor-eating brownouts during summer heat waves, and the ever-present threat of a violent storm that might rip down power lines.

The unpredictability of outages gives stationary, permanently installed standby generators a clear advantage over their portable, gas-powered kin, which resemble big lawn-mower engines on dollies. A portable has to be rolled outside, started manually, and plugged in to the house electrical system, a process that takes several minutes at least—if someone is at home to do it. And if an outage lasts more than a few hours, a portable's gas tank is likely to run dry. A permanently installed standby generator, by contrast, is always ready to go and can run nonstop for days, fueled by a natural gas line, or tanks of propane or diesel.

<p><strong>Anatomy of a Generator</strong><br>When the power goes out, this automatic standby installation switches to emergency mode, starts the generator, and feeds power to designated emergency circuits in the house.</p>

Anatomy of a Generator
When the power goes out, this automatic standby installation switches to emergency mode, starts the generator, and feeds power to designated emergency circuits in the house.

Illustration by Ian Warpole

The All-Important Transfer Switch

When the power goes out at the Wymans', they have to flip a manual transfer switch (which isolates the house from the incoming power lines), then push the button that fires up their unit. For another $1,000, an automatic transfer switch could do all that work for them. This brainy device constantly monitors incoming power, and when it detects an interruption or a serious voltage reduction (a brownout) automatically isolates the house and starts the generator. All told, the process takes 10 to 20 seconds. "You're going to be in the dark for a few seconds, but the power will come back up as soon as the generator comes on," says Bill Perry Sr., owner of Central Maine Diesel and installer of the Wymans' system. The reason for the delay is that the transfer switch waits to see if the power will come back on, so that the generator won't cycle on and off every time the lights dim. When power from the utility returns, the transfer switch waits for a sustained flow of current before it shuts the generator down.

The first step in choosing a generator is to determine how much electricity your household needs in an emergency. That will tell you how big the generator's output needs to be. Small 4- to 8-kw units, for instance, can power lights and a few critical appliances, while the 25-kw behemoths allow a household to function as though the power lines never went down. A 10- to 15-kw generator, the size most commonly used for residences, is usually sufficient to power most home appliances, including such energy-suckers as water heaters and window air conditioners. To keep power needs (and generator size) in bounds, an essential-loads distribution panel is a necessity. Only circuits that require emergency power are connected to the panel. Normally, it receives and distributes power from the utility, but during an outage, after the main transfer switch is activated, this panel gets all its power from the generator. (When the outage is over, the panel reverts to utility power.)

A properly sized generator should deliver 10 to 20 percent more power than the total expected demand. Running a unit too close to its rated output reduces fuel efficiency and makes the engine run harder. If completely overtaxed, the generator's breakers will trip (to protect it from overheating). "A generator that's too small is worse than not having any power at all," says Ron Ford, sales manager at Kohler, which manufactures both residential and industrial generators.

You pay a substantial price for the convenience of a permanently installed generator, and that price increases substantially as output goes up. It starts at about $3,000 for the 6- to 8-kw models and reaches from $5,000 to $10,000 for the 11- to 20-kw units. Add to that anywhere from $800 to $2,500 for installation, including pouring a concrete pad, wiring, and installing a fuel line and tank, all of which are coordinated by the dealer. (Find them in the yellow pages or through manufacturer Web sites.) Plus, there's the cost of maintenance and fuel.

<p><strong>Table for ''Sizing a Generator''</strong></p>

Table for ''Sizing a Generator''

Sizing a Generator

To figure out how big your generator's output needs to be, make a list of all the appliances you'll need during an outage and add up their surge watts—the amount of electricity a motor needs to start (see image 3). Add to this total the run watts for electrical items without motors, such as lightbulbs, water heaters, and television sets. To this sum add a 10 to 20 percent safety margin, then divide by 1,000 for the kilowatt rating you should look for in a generator.

According to Ron Ford, a sales manager at Kohler, this calculation ensures that a generator will be big enough to cope with emergency power demand while running at ½ to ¾ of its maximum load, which reduces fuel consumption and wear and tear on the engine (see image 2).

Generator Maintenance

A permanently installed generator is a bit like owning an extra car, although it should last considerably longer. The engines can run for 1,500 to 3,000 hours, which, considering the short length of most outages, amounts to a life span of about 15 to 20 years. To make sure the engine works when you need it, most installers offer annual service contracts ($200-$250) for changing the oil and air filter, checking the starter battery, and testing the system. Unlike cars, some generators automatically "exercise" themselves for a few minutes once a week to circulate oil and recharge the battery. (No power is fed to the house at those times.)

Other than size and price, some features to look for include:

•Electronic voltage regulator, to stop the fluctuations that can harm electronics.

•Ease of accessibility for maintenance.

•Weatherproof, insulated housing to dampen engine noise. "The smaller, 8.5- to 11-kw units are pretty quiet," Ford says. Bigger generators, he admits, are much noisier.

The noise and occasional oil change are only minor inconveniences to the Wymans. "We should have done this a long time ago," says Jasper. "Now, I'd be very uneasy without my generator."

What About the Computer?

A computer system stands to lose gobs of important data in the 10 to 20 seconds between the time the power goes out and the generator starts pumping electricity. The solution: battery backup, also called an "uninterruptible power supply" or UPS.

It takes just milliseconds for these gadgets to detect a power outage or a voltage fluctuation (either a surge or a brownout) and step in with their own "clean" supply. A typical home computer won't even notice the interruption. Some UPS models have the ability to shut down a PC automatically after a certain amount of time, in case no one is home during the outage.

There are $50, breadbox-size UPS units that can run a computer and monitor for 10 minutes—long enough for you to save work and shut down. Or you can buy big 5-kw banks that cost $5,000 and will keep a few critical circuits in the house going for several hours or days (if used sparingly).

Aside from occasional testing, a UPS needs no maintenance. Its sealed battery is kept recharged by the home's electrical system. Expect one to last 7 to 10 years with no noticeable decline in output, says Rob Heckenast, of Xantrex Technology Inc., a manufacturer of battery-backup systems.

Because batteries run out of juice fairly quickly, Heckenast says, the best backup systems use a combination of power sources. "For the full-meal deal, get batteries for brief outages and a standby generator for the long blackouts."

Where to Find It

Portable generator:

EB5000XK1 by Honda Power Equipment Group

Alpharetta, GA


Uninterruptible power supply:

American Power Conversion Corp.

West Kingston, RI


Generator distibutor:

Central Maine Diesel

Bangor, ME


Our thanks to:

Ron Ford & Garrett Mersberger of The Kohler Co.

Kohler, WI


George Amidon

Kraft Power

Woburn, MA