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Illustration by Geoffrey Grahn

One out of three American homes is more than 50 years old, and while historic architecture inspires passionate renovators, outdated electrical systems can be intimidating for novices to tackle. But a recent study finds that old wiring isn't always a problem. "The wiring in old homes is holding up remarkably well," says John Drengenberg, a spokesperson for Underwriters Laboratories, the product-safety testing organization, which coauthored the study with the Fire Protection Research Center. While the wires themselves may be in fine shape, overloading a home's wiring system and taking DIY shortcuts are two of the major reasons behind the 32,000 electrical fires that occur in homes each year, which cause a whopping $674 million in damages. "Sometimes homeowners make changes that compromise the safety of an electrical system," says Drengenberg. "For example, you might start twisting and hammering wires into outlet boxes or taking other shortcuts. Remember, houses built in the '20s and '30s were designed to handle a toaster, a couple of lamps, and maybe a washing machine—not 48-inch flat-screen TVs in every bedroom."

A few scenarios cry out for a certified electrician's help. Flickering lights and frequently blown fuses mean you're overburdening the system. Using an excessive number of extension cords to power your everyday appliances means you need more electrical outlets. And if your outlets are too hot to touch or emit a burning smell, it's a sign that your wires are throwing off sparks behind the wall. If any of these things should happen, call in the pros. But no matter what shape your wires are in, these preventive steps will help you avoid bigger problems in the future:

1. Stop overloading a single circuit, which often happens when you plug two or more heat-producing appliances like toasters, microwaves, and ranges into the same outlet.

2. Don't "overlamp" by putting a 100-watt bulb into a socket rated for 40 or 60 watts. The additional heat damages the wires' insulation over time, making them dangerously brittle.

3. Avoid taking shortcuts with DIY projects. Spending extra time to make sure you don't pinch wires when you screw something into the wall could save you from a calamity in the future.

4. Repair or replace worn wiring on appliances. This is one common hazard you can easily monitor and control.

5. Never run cords for appliances under rugs. A flammable rug and trampled, fraying wires make a deadly combination.