Hurricanes, terrorist attacks, the giant blackout on the Eastern seaboard in the summer of 2003 and fears of power loss due to Y2K problems have put a spotlight on standby generators since the late 1990s. Rolling blackouts and brownouts in California a couple of years ago demonstrated how increased electrical demand is stressing the power supply on a daily basis, making everyone more susceptible to the threat of power loss. When you think about how vulnerable the power grid is to attack or failure, a generator seems more of a practical investment than a luxury.
If you're lucky, you'll never need a standby generator. But if your electrical service goes out for an extended period, a generator can not only make your home more comfortable but also prevent disasters such as frozen pipes or a refrigerator full of spoiled food - even if you're not there to switch it on. Here's what you need to know to find the right system for your home.
Generator basics
A residential standby generator is a stationary 2- or 3-ft.-tall metal box that resembles a central air conditioner and is mounted outdoors on a pad. A typical model weighs 400 to 1,000 pounds and has a footprint that covers roughly 12 sq. ft. Installation requires an electrical permit in most areas and should be performed only by professionals.
The generator is a dedicated appliance. It connects to the home's electrical service panel through a transfer switch that signals the generator to take over if utility power fails. Transfer switches can be either manual (in which case you have to turn on the generator and plug it into the switch panel) or automatic. A standby generator should be wired through an automatic transfer switch that contains a monitor so it can make the power feed switch automatically. Manual transfer switches are intended for use with portable generators that are not connected to the home in permanent standby mode.
Although diesel models are available, most standby generators are powered through the home's natural gas supply lines, so they have an unlimited source of clean fuel. If your home does not have a natural gas supply, a generator that operates on tanks of liquid propane (LP) is an alternative that prevents you from having to stockpile a fresh supply of gasoline or diesel fuel.
Even the best standby generators are not intended for ongoing service because the LP or natural gas that powers them is considered "dry fuel," according to Jim Flowers of Cummins Power Generation, manufacturers of the Onan brand of residential and portable generators and related products. Generators powered by diesel or gasoline last many times longer because the fuel contains lubricants that help to protect the engine cylinders. Most generators that are relied upon to supply power on an ongoing basis are fueled by diesel or gasoline.
Homeowners who are considering investing in a backup power source may question spending $5,000 or more on a generator that is designed to provide only short-term emergency power. After all, for a fraction of that amount you can buy a portable generator that not only can be hooked to a transfer switch for emergency power but also can be used for other purposes such as camping and powering tools in the field.
For homeowners with smaller budgets, a portable model and a manual transfer switch may make sense. But portability can be a disadvantage - what if a home power outage occurs when you've taken the generator camping? Other potential problems with these setups surface if a power outage occurs when you're out of gasoline or away from home and can't access the transfer switch. In addition, a well-used portable generator may fail during a long outage - many air-cooled units have a life expectancy as short as 500 hours.
If you own a gas-powered generator with a capacity of at least 3 kilowatts (kW), it may make sense to have a manual transfer switch installed so you can plug the generator into it in an emergency (see Web Extra). But for truly automatic and self-sustaining power backup, a standby generator is worth the investment.
Shopping for a system
The smallest standby generators supply 6 to 8 kW of power and cost $2,000 or more. An average-size 12- to 15-kW model (starting at $3,000) yields as much as 50 amps of power, which is enough to operate several light circuits and a few major appliances. For the homeowner who refuses to be inconvenienced in any manner by a reduction in power availability, 25- to 40-kW standby generators (starting at $10,000) will provide full service to a 200-amp panel. A normal-size house (about 2,500 sq. ft.) can be adequately served by a 12-kW generator and a 100-amp automatic transfer switch, provided you manage the electrical flow wisely. Plan on spending $6,000 to $8,000 for an installed system of this size.
If you consider air conditioning a necessity, you have more options today than were available a few years ago. Experts used to recommend 17- to 20-kW models as a minimum. But technological advances in the industry have enabled several companies to produce less powerful (and more efficient) standby generators that can still power an air conditioner. These units apportion out the initial surge in demand that occurs when an appliance (particularly an air conditioner) starts up.
Kohler Power Systems' new 12-kW standby generator is billed as capable of delivering enough power to operate a 48,000-Btu (4-ton) central air conditioner. And Briggs & Stratton has just introduced its IntelliGEN standby system that actively and sequentially manages the cycling of up to six highwattage household circuits and two 4-ton cental air circuits. GenTran, a maker of automatic and manual transfer switches, recently introduced its Powerstay automatic power transfer system, which also uses load management and sequencing to allow homeowners to get by with a smaller generator.
Most standby generator systems are sold through distributor-installers. Larger building centers and power equipment dealers carry a limited selection of standby sets and transfer switches. As you're comparison shopping, keep in mind that quoted prices often do not include the transfer switch and various installation accessories. You can buy a transfer switch for about $200, but better-quality ones cost $1,000 or more. If you're considering buying a complete kit (usually sold on the Internet), also consider that prewired conduit included in some packages may not be usable in your installation.
Transferring power
An automatic transfer switch is a gatekeeper for the electricity that enters the home's service panel. When normal utility power is functioning, the current flows unabated through magnetic contactors in the transfer switch and into the main panel. But when utility power is interrupted or reduced, the contactors lose their magnetic connection. If power is not restored within 10 seconds or so, the switch sends a signal to a battery located on the generator set, starting the unit.
Once the generator is producing adequate power, the switch directs the electricity into the service panel and shuts off the connection to the utility power. Among other benefits, this prevents the generated power from back-feeding into the utility line, which can pose a serious safety hazard to utility workers. When the normal level of utility power is restored, the switch shuts down the generator and reconnects the home's panel to the utility power.
Transfer switches are made to match typical home service panel sizes: 60-amp, 100-amp and 200-amp. As with service panels, the amperage rating determines how many electrical circuits you can power through the transfer switch. It's fine to attach a 100-amp switch (the most common size) to a 200-amp service panel, but never install a switch with a larger amperage capacity than the service panel.
Some transfer switches are paired with an auxiliary load center so you can select which circuits are protected by the standby power. This eliminates the possibility that you may overload the generator, which normally results in the tripping of a breaker aboard the generator set. The breaker needs to be reset manually before the generator can resume operation.
You can hook a switch directly to the power service entry point on the main service panel, however, even if the generator produces only a portion of your normal electrical flow (for example, a 50-amp-output generator hooked into a 200-amp panel). As long as the electrical draw doesn't exceed the output capacity, it won't trip the breaker. If you choose this setup, power management becomes more of a necessity. Switches that are designated as transfer panels include both the switching device and power distribution buses and breakers for vital electrical circuits, such as the refrigerator and lights.
As you contemplate an emergency backup power system, consider that in the vast majority of occasions when a standby generator system is called into duty, it seldom has to run for more than a few hours. Decide what your basic needs are and choose the system accordingly. Although you don't want to skimp on capacity and features, there's no point in paying for power you can temporarily live without.