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Standby generators: Power plus

The blackout in August 2003 that left 50 million people in the Northeast without power for days and power interruptions in 2004 in the wake of successive hurricanes that struck Florida and the Southeast alerted many homeowners to the need for backup power.

Whether they are caused by human error, catastrophic weather events or simply utility overloads on old and overtaxed power lines, power outages can last days and even weeks. And the chances of that happening are increasing. Statistics show that electric power outages lasting at least 24 hours have tripled since 1978.

For security and peace of mind, as well as protection from the sometimes damaging effects when the power goes off, more homeowners are turning to permanently installed residential standby generators.

Why backup power?

A standby generator can keep the lights on whenever there's a power outage in your neighborhood.

Power outages affect different people in different ways. An outage that is inconvenient for one family might have far more disruptive, even disastrous, consequences for another.

For a homeowner relying on a sump pump to keep water from rising into living areas during a storm, for instance, backup power can prevent damage to rugs, furniture and valuable electronics. During winter, backup power can stop water pipes from freezing and bursting.

When considering a backup power source, most homeowners think first of a portable generator. Although this can be an effective solution, it does have drawbacks. During a power outage, the homeowner has to haul the generator out of the garage, start it and run extension cords from the generator to appliances.

Typically, portable generators run on gasoline, which may not be readily available during an extended outage, and they must be operated outdoors, which can be less than ideal in inclement weather. In addition, a unit usually requires refueling after eight to 10 hours of operation, as well as periodic testing and maintenance to ensure it remains in working order. That said, when used properly, a portable generator is a safe way to provide backup power.

How it works

The standby generator, which resembles a central air-conditioning unit in size and form, is installed outside the home. An automatic transfer switch is installed inside next to the home's circuit breaker panel. A secondary circuit breaker panel is required only if selected circuits are designated to run off the generator. A second panel is not required when the generator is sized to power the entire house.

The transfer switch monitors the condition of power from the utility. When there is a utility disturbance of more than a few seconds, the transfer switch signals the generator engine to start. After a few more seconds, when the generator is at full power, the transfer switch disconnects from the utility and brings the generator online.

Typical response time varies among manufacturers and between units, with some units restoring power as quickly as seven to 10 seconds after a blackout or brownout is detected. Others take 10 to 15 seconds, or even a bit longer.

In a critical application for which any time without power is too long, a homeowner should use an uninterruptible power supply (UPS), which is battery powered, to carry any essential circuit load until the generator takes over.

When utility power is restored, the transfer switch transfers the electrical load back to the utility. Everything happens automatically, without homeowner intervention.

Installation and costs

Installation is straightforward and does not require rewiring your home. All wiring is between the generator, the transfer switch and the electrical panel.

Residential units start at 5,000 watts (5 kw). A 7,500- to 8,500-watt unit is usually enough for running essentials in an average home.

Generally, units up to and including 12,000 watts (and, from at least one manufacturer, including 15,000 watts) come with a composite base pad, which is laid atop a bed of level gravel. Larger generators require a site-prepared concrete pad.

A 7,000-watt standby generator with an air-cooled engine and prewired with a transfer switch starts at about $2,000, with installation perhaps another $750 to $2,000, assuming the fuel feed and electrical panel are in close proximity. At the high end, a unit providing 47,000 watts of standby power costs about $22,000, plus installation.

Units up to and including 12,000 watts come with air-cooled engines, while units larger than 15,000 watts are powered by liquid-cooled engines. (Units offering 15,000 watts of power are available in both types.) Air-cooled generators run at a higher speed and are noisier than liquid-cooled generators, which use car engines with radiators to keep them cool.

Standby generators come in weatherized enclosures of galvanized steel or aluminum that are designed to protect the engine and other components from the elements. The enclosures incorporate insulation and/or sound-dampening technology to muffle the operating noise down to a level not much louder than a home vacuum cleaner or a central air-conditioner compressor.

The systems have a life cycle of between 3,000 and 10,000 hours, and typically require an occasional oil change and replacement of spark plugs.

To ensure that the generator will operate properly when called upon, residential standby units automatically run for a few minutes every so often, at a predetermined frequency. The PowerStation from Coleman, for instance, conducts biweekly self-tests to ensure reliable operation.

Given the range in size and costs of generators, it's important to evaluate your needs carefully before purchasing a unit. Most manufacturers recommend that homeowners consult a professional to help them determine the proper size of a standby generator system to meet their requirements.

Generators rated between 11,000 and 15,000 watts, which can power nearly everything in a midsized home, are the most commonly installed units. Homeowners watching their budget can opt for a smaller unit and limit distribution of the standby power to critical devices and appliances -- say, the furnace, lighting, sump pump, refrigerator, security system and garage door opener. For larger homes or for homes where the intent is for the standby generator to provide all the power normally consumed, including power for central air, homeowners can opt for larger units between 20,000 and 60,000 watts.

When considering size, it's important to choose a unit that can accommodate initial power surges. Appliances with electric motors, such as refrigerators and air conditioners, require more watts for a few seconds at startup than they use during normal operation. A window air conditioner rated at 1,200 watts, for instance, has about 4,800 surge watts.

As a rule of thumb, the residential generator wattage capacity should cover the total wattage of all devices and appliances that a homeowner will want to run with the generator, plus the extra wattage needed to start the most watt-hungry, surge-producing devices.

Typically, manufacturers of standby generators have charts available on their websites or in hard copy that show the rated watts and surge watts of most household appliances. They also generally have guidelines showing typical items that can be powered by each capacity generator they sell, so you can choose the unit that best meets your needs when the lights go out.