The knowledge of power

If you have ever traveled overseas, you already know that electricity is not served the same way everywhere. Whether you're packing a travel iron, a computer or an iPod, you must be aware that the type of current, voltage levels and wall plugs vary dramatically in different places. This can be frustrating, costly, even dangerous for the unprepared.

Current is delivered at either 100 to 120 volts (in 39 countries, including the United States, Canada, Mexico, and most other nations in Central and South America and islands in the Caribbean) or at 220 to 240 volts (in 139 countries, including most of Europe, Asia and Africa). Exceptions to these general rules are numerous, and in some countries the electrical service varies: 110 in some areas, 220 in others.

Running an electrical device designed for 110 volts on 220-volt current will make it work twice as fast or hot, and will likely fry the circuitry. Operating a device on a lower voltage than specified won't produce the desired result, either.

Voltage is not the only issue. Alternating current (AC) is the operating standard in most places, but large swaths of Argentina, Brazil, India and South Africa use direct current (DC), as do many ships. Even the AC standards vary. In the United States, the AC current alternates 60 times a second, but in many places, it cycles just 50 times a second. The difference probably won't harm an appliance, although devices that depend on the electric cycle for their timing will run slow.

Some appliances are designed to run on dual voltage and can easily be changed to accommodate different electrical systems. The battery chargers that come with most portable computers, for example, are usually dual voltage. Other appliances require a power converter or transformer.

Simple electrical converters that step voltage down from 220 to 110 and in reverse can be purchased in computer, travel and department stores. Low wattage converters are designed to work for appliances that draw no more than 50 watts of power. High wattage converters are for appliances that draw up to 1,600 watts, commonly heat-producing devices such as hair dryers, irons, hot plates, coffee makers, curling irons and heating coils.

Converters are not intended for appliances that are used for long periods, such as power tools, or for appliances with delicate electronic circuitry, such as computers, fax machines, cell phones, cameras. For them, you'll need a step-down transformer.

Step-down transformers come in several sizes, based on the electrical requirements of the appliance you're using. Common ratings are 100, 250, 500 and 1,000 watts. The larger transformers may be heavy, which is a definite consideration if you'll be carrying your own luggage.

Every electrical device carries information about its voltage and wattage requirements listed on the manufacturer's label on the back or bottom of the device.

Always use a transformer rated at least 10 percent higher than the appliance. An appliance that uses 300 watts will require a 500-watt transformer. Also remember to unplug the converter or transformer when not in use to prevent overheating. And be aware that if you buy any devices overseas that require 220 volts, you will also will need a "reverse" transformer for it to run once you get home.

Electrical connections are the other primary concern. The world has five basic plug configurations. The one we use, two flat, parallel prongs, is fairly standard throughout the Western Hemisphere, at least in those countries that run on 110 AC. In most of Europe and Asia, however, electrical plugs have two, fat, round prongs. In Britain and Ireland, plugs generally have three flat or two oversized round prongs. In Australia, New Zealand and much of the South Pacific, plugs have two flat prongs, but they are set at angles. And there are at least eight other plug and socket configurations in use in particular countries around the world. Make sure to take an adapter that will let you fit a grounded plug into a two-prong socket.

Basic 5-electrical plug and power converter kits should cost about $20; heavy duty step-down converters can run considerably more.

The bottom line: Before you travel overseas, make sure you're prepared to accommodate the local power. Several Web sites offer listings of electrical standards and plug requirements for foreign countries. One comprehensive site is users.pandora.be/worldstandards/electricity.htm.