You might not be aware of it, but all extension cords are not created equal.

Wire expands and contracts as electrical energy passes through it. When the draw on the wire is greater than what it is designed to carry, the wire is taxed. Over time, this might cause it to become brittle and result in a short that in turn could damage the sheathing and ultimately result in a fire.

Less important, but nevertheless a consideration, is how the cord affects the performance of an appliance or tool. Using an extension cord that doesn't supply the required power can cause the tool or appliance to operate below its rated capacity. This condition could make a job more difficult and result in damage to the motor.

The power that an extension cord will deliver is determined by several factors. A couple of the most significant are the "gauge" of the wire and the length of the cord. Extension cords come in a variety of wire sizes known as gauges. The most common are 18, 16, 14, 12 and 10. The lower the number the heavier the gauge of wire. Thus, 12-gauge wire is heavier than 14-gauge. The heavier the wire, the more amperage it is able to safely conduct. Therefore, a regular duty extension cord of, perhaps, 16-gauge wire can be used for a table lamp. This is in sharp contrast to a circular saw that will require more power. In the latter case, a heavy duty extension cord of 12-gauge wire should be used.

To determine the proper gauge extension cord for a tool or appliance, locate its amperage or wattage. This typically is displayed on a metal plate located somewhere on the housing. Most extension cords will contain a label with a rating. When in doubt, use an extension cord that is heavier than what is required, never lighter. Remember, the heavier the cord the lower the gauge number. You might pay a bit more for a heavy-duty cord, but it will give you the peace of mind of knowing that it can be used safely in most situations.

The second factor is the distance that the cord must travel. The ability of any cord to carry electricity decreases as the cord's length increases. So, in situations where you might otherwise be able to use a medium duty, 14-gauge extension cord, you may need to upgrade to a heavy duty, 12-gauge one when making a longer run. For example, a medium duty 14-gauge extension cord will deliver 15 amps given a run up to 50 feet. This is sufficient to safely supply power to a 1-horsepower motor. The same cord, 100 feet long, will deliver 13 amps, enough to safely power a horsepower motor.

If your tool or appliance has a ground plug, the extension cord and the wall outlet must also have ground connections. Never plug a 3-prong adapter into a 2-prong cord to get power to a tool. Newer extension cords, tools and appliances are "polarized" with one slot and prong wider than the other. It is important that they be matched correctly when connecting them.

Extension cords are rated for indoor or indoor-outdoor use. Cords rated for outdoor use are heavier duty, with superior insulated wire, plugs and receptacles. The wires are individually insulated and all wires are wrapped together with an outer sheathing or "jacket."

Outdoor cords bear the designation "W-A." Flat extension cords with the outer layer serving as both wire insulation and the protective outer jacket are rarely rated for outdoor use, and hence should never be used outdoors.

Some cords are equipped with a Ground Fault Circuit Interrupter (GFCI) receptacle. This contains a sensitive, circuit breaker-like mechanism that offers added protection against shock when tools or appliances are used in damp or wet areas.

There are some basic do's and don'ts that should be noted when using an extension cord. Always unplug them when not in use. Children and animals love to chew on them. Children also like to poke things into the receptacle end. Don't use a cord that's hot to the touch. It's a sign that the cord is overloaded.

Always fully uncoil an extension cord before using it. A coiled cord builds up heat and in extreme cases the jacket can melt, creating a fire or shock hazard. Don't let cords or connections sit in wet areas or outside for extended periods of time. The sun's ultraviolet rays can make the outer jacket brittle. Oils and grease can soften or degrade the cord's jacket. And never unplug a cord by pulling on the cord itself; always grip the plug or receptacle end.