When you plugged in your new refrigerator, cranked up the air conditioner, or turned on the light to read this report, you probably didn't give a lot of thought to the wires carrying the electricity.

Few people do. After all, your home's electrical system is hidden in the walls. Homeowners and renters generally know so little about electricity that they tend to take potential problems too lightly or overlook them altogether.

But you need to pay attention to your home wiring no matter when your home was built or where you live, especially if you live in an older home. Thirty-nine thousand house fires and 350 deaths each year in the U.S. are caused by faulty home wiring and other electrical equipment, such as extension cords, lighting, and plugs, according to the National Fire Protection Association.

And at a time when many homes are increasingly susceptible to electrical problems, government oversight that's supposed to protect homeowners and renters is often fragmented and ineffective, Consumer Reports has found. Consider this:

U.S. household electrical use

Source: Edison Electric Institute

The nation's housing supply is aging. One-third of all homes--30 million--are more than 50 years old; half are at least 30 years old. Older homes often fall short of today's electrical-safety standards.

Older homes in particular were not designed to handle rising electrical demand. Appliances may be more energy efficient than in the past, but they're bigger and we're using a lot more of them, which chronically stresses many homes' electrical systems.

New electrical work in homes is supposed to be safeguarded by a system of licensing, permitting, and inspection by local officials. But homeowners often bypass that route because it takes more time and money. And governments are cutting staff and budgets for that critical oversight, or not paying for it to begin with.

Problems with existing electrical systems--worn-out equipment and jerry-built "fixes" by successive owners of a home or an apartment building--may never be discovered. Localities typically don't require an electrical inspection when a property changes hands.

Debbi Porterfield thought her family was doing everything right when they bought their house in Rye, N.Y., which was built in 1875. Though the village didn't require inspections before or after the sale, Porterfield hired a home inspector whom the real-estate agent recommended. The inspector noted mostly minor problems.

So Porterfield, 44, a freelance writer, was concerned when a more thorough inspection by a licensed electrical contractor hired by Consumer Reports turned up some dangerous conditions. Burned wire insulation in a bathroom ceiling light, probably caused by a bulb with wattage too high for the fixture, could have started a fire near the children's bedrooms. In the garage, a hanging light with frayed insulation posed a threat of electrocution or fire.

"I was a little bit stunned by what the inspector showed me," Porterfield said of the electrical contractor.

Overall, the number of reported house fires has declined for two decades, thanks in part to smoke alarms that provide early warning. (See our tests of Smoke alarms.) But fires caused by faulty electrical systems--bad wiring or components damaged by age, misuse, or poor alterations--still worry fire officials. An 18-agency federal task force has called aging wiring in homes, buildings, power plants, and transportation systems an important national safety issue.

"Fifty-million homes are approaching the end of life of their wiring systems," says William King, a chief engineer at the Consumer Product Safety Commission (CPSC). "It's an urgent problem."

Now federal officials and safety groups are trying to get the word out that frequently blown fuses, hot or dead outlets, and other problems aren't just nuisances; they are serious warning signs of electrical hazards that can result in disaster if not addressed. Experts are also emphasizing that home wiring needs to be maintained, upgraded when necessary, and periodically inspected by a qualified, licensed electrician.

How do you take stock of your home? What hazards should you look for? How do you choose an electrician? Read on.

Given the nation's housing stock, it's not hard to see why so many homes have electrical-wiring problems today.

In the oldest homes--those, like Porterfield's, that are a century old or more--electricity was a retrofit, installed mainly for lighting, sometimes through former gas-lighting pipes or porcelain tubes. Typically, these houses were wired at 30 amps--enough to power basic lighting and some kitchen appliances, but not much else.

By the late 1940s, 60-amp service was common--better, but still short of the 150- to 200-amp service typical of new construction. (In the biggest new homes, 800-amp and up isn't uncommon.)

Old wiring, by itself, doesn't necessarily mean trouble. But you have to be careful that the insulation protecting the wiring is in good shape. Insulation can become damaged when it is rubbed or pierced, or even when a circuit is heavily loaded. When that happens, the wires get hot and, over time, the insulation can crack or fray.

Often, older homes are not grounded to minimize the risk of shocks, and they typically have too few outlets for today's demands--sometimes as few as one per room--which can lead to a dangerous reliance on extension cords. By contrast, contemporary codes typically require a wall outlet at least every 12 feet.

Beginning in the 1950s, wires were insulated with tougher thermal plastic instead of fabric or rubber; three-prong grounded outlets replaced two-prong ones; and circuit-breaker panels replaced fuse boxes. Both circuit breakers and fuses are designed to shut off power to their circuits if more current flows through circuits than they should carry. Experts consider circuit breakers more convenient and safer because they're more tamper-resistant.

When fuses blow, circuit breakers repeatedly trip, or lights often dim, it's a sign that there is a problem with the wiring or that you are overstressing the circuit and may need a new one or a service upgrade. Yet homeowners have been known to make quick, often illegal fixes, such as using fuses that are overrated for the circuit they're protecting (20-amp fuses on a 15-amp circuit, for example). Overrated fuses don't protect circuit wiring from overheating because they allow more current through the wiring than the wiring was designed for.

Electrical fires can occur from a phenomenon called arcing, in which current "jumps" through a tiny gap of air, such as between two ends of a broken wire or at a loose connection to a receptacle. Arcs are extremely hot and can heat nearby material, such as wood or some types of insulation, which can smolder for hours before bursting into flames.

Other electrical fires can be caused by overheated components such as switches that ignite other material.

Another potential problem affects some homes built between the mid-1960s and the mid-1970s. Builders of about 2 million homes at that time substituted less expensive aluminum wiring for standard copper wiring in the branch circuits, which are the wires that distribute electricity to each room from the service panel. But the aluminum branch-circuit wiring was later found to oxidize and loosen at connections, causing arcs and overheating at switches, outlets, and the breaker panel.

In 1977, the CPSC unsuccessfully sued to get aluminum branch-circuit wiring recalled. The commission ended up warning homeowners about the need for repairs through a public-information campaign. But tens of thousands of home electrical systems never were repaired and still run the risk of fires, federal officials say.

The risks are real. Aluminum house wiring played a role in a fire that killed five people in Morris County, N.J., in March. Fire officials said the home, built in 1968, had aluminum branch circuits that someone had improperly repaired. (For more on this issue, check CPSC publication 516 at www.cpsc.gov/cpscpub/pubs/516.pdf.)

Homeowners who do their own electrical work or hire an unqualified friend can create some of the worst hazards. Since these homeowners often avoid inspection by skipping the building-permit process, the hazards can go unnoticed for years.

"Ignorant, amateur wiring is the most common, real dangerous thing that I see," says David E. Shapiro, a Washington, D.C.-area master electrician who has written extensively about wiring hazards. Those include thin-gauge lamp wire run behind walls to bring electricity to another room, mismatched-gauge wire, and badly spliced wires, Shapiro and other electricians say.

THE PROBLEM Damaged wires and loose connections create a fire hazard called arcing. The phenomenon is shown here in a lab test when an extension cord is pierced.

Even in new homes, homeowners should be mindful of potential problems. Just ask Tom Meenan of Silver Spring, Md., who discovered a burned cable, dead circuits, and other problems in the $325,000 townhouse he bought new two years ago.

"I rarely used the dishwasher, and the third or fourth time I ran it the circuit went dead," says Meenan, 45, an information technology manager for the U.S. Senate. "There was severe arcing in the breaker panel." Meenan hired an electrical inspector, who found other problems, including a poorly wired electric furnace. He says he is still negotiating with the builder for repairs.

If you are experiencing flickering lights, hot outlets, or other warning signs, disconnect appliances on overworked circuits. Then hire a qualified, licensed electrician to inspect your home and make repairs. To find an electrician, seek recommendations from satisfied neighbors. If your state requires licensing, check the electrician's license number with the appropriate state or county agency and contact the local Better Business Bureau about any previous complaints. When you hire the electrician, obtain an estimate in advance, and ask the electrician to list priorities and specify costs.

You should have an electrical inspection when you buy a house. The Electrical Inspection Code for Existing Dwellings (NFPA 73), intended for use by general home inspectors and electricians, can be a good resource for homeowners. It's $21 from the National Fire Protection Association (800 344-3555, or 617 770-3000 outside the U.S.; www.nfpacatalog.org.)

Other resources are the CPSC's free guide to home electrical hazards, at www.cpsc.gov/cpscpub/pubs/518.pdf, and a safety checklist from the National Electrical Safety Foundation, atwww.nesf.org.

The CPSC recommends home inspections every 20 years. That's 20 years from the time the home was last inspected, not 20 years after you moved in. If you've added high-wattage appliances or renovated, you should consider an inspection sooner.

Most local governments require that you obtain a permit before having major electrical work done and that the work be approved by a qualified electrical inspector. But even without such a requirement, you should have the work inspected upon completion. If your area doesn't have city or county inspectors, your local fire department or building department may be able to help you find one. So can the International Association of Electrical Inspectors, in Richardson, Texas, at 972 235-1455.

A promising new technology you may want to consider is the arc fault circuit interrupter (AFCI), which detects arcs at low levels of current that wouldn't trip a circuit breaker. An electrician installs these devices in your circuit-breaker panel. They're not a substitute for replacing bad wiring, but they do offer added protection for older wiring.

The CPSC wanted the newest national electrical code to require installation of those circuit interrupters during any upgrade of a service box, King, the commission's chief engineer, says. But the proposal was defeated by other members of the code-making panel. "We don't feel the research is there" to justify the cost, says Jeff Inks, a member representing the National Association of Home Builders.

The national electrical code will require the circuit interrupters in all bedroom circuits of new homes beginning Jan. 1, 2002.

Not all states adopt the latest national electrical code, however. And across the nation, licensing, permitting, and inspection requirements are patchwork and, in some cases, nonexistent.

A decade ago, a CPSC study noted that "training or qualification of electrical workers is not regulated or enforced" in many jurisdictions and that "many districts outside major metropolitan areas effectively have no electrical inspection."

Since then, there's been even less government enforcement of licensing and inspection, because of rapid growth in some areas and budget cuts in others.

Several years ago, the CPSC tried in vain to promote mandatory electrical inspections at the time a property is sold. "We were met with less than a lot of success," King says. "Nobody wants additional burdens."

So the commission focused instead on public education and promotion of new technologies, such as AFCIs, in new construction, King says. But new-construction codes won't prevent fires in the millions of older homes that may be at risk.

Safety groups have been pushing local lawmakers to improve the inspection process for new and older homes. Until more state and local governments get serious about home wiring, electrical fires will continue to claim lives and property.