When it comes to choosing an extension cord, size and length are important. Using a cord that is too light or too long can damage equipment and create a fire hazard. Knowing the right information will help you make the right choice.

Step 1: Extension cords come in a variety of sizes and lengths. The thickness of the cord does not necessarily correspond with the thickness of the wire. Heavy duty cords often have extra thick insulation around the electrical wire. Look for the American Wire Gauge (AWG) number on the cord to determine the actual wire size or gauge. The smaller the number the thicker the wire; an 18-gauge cord is a light-weight cord and a 12-gauge cord is a common heavy duty cord.

Step 2: As electricity travels from the plug to the end of an extension cord some power is lost. Smaller wires and longer cords lose more power than their heavier gauge, shorter counterparts. A 100-foot 18-gauge extension cord will lose approximately 23.4 volts from start to finish. A 16-gauge cord will lose 15.1 volts, 14-gauge will lose 9.4 volts, 12-gauge will lose 5.9 volts and a 100-foot long 10-gauge cord will only lose 3.7 volts. Assuming 120-volt service, 100-foot 18-gauge extension cords can only deliver 96.6 volts to any piece of equipment and so forth.

Step 3: A little math can help determine how much power is needed to run any piece of equipment if the equipment is labeled with its maximum amp requirements or maximum wattage output. Amps are equal to wattage divided by volts. Given a typical 120-volt system, a 1500-watt heater requires 12.5 amps of power.

Step 4: It is wise to never push any electrical service to its limits, so when calculating power needs, leave a 20 percent margin of error. Or skip the math and follow these guidelines:

— Use an 18-gauge cord up to 25 feet long for lamps, clocks and other small electronics that require less than 7 amps of power.

— Use a 25-foot 16-gauge cord or a 50-foot 14 gauge cord for televisions, laptops and small appliances that require less than 12 amps of power.

— Use a 50-foot 12-gauge cord or a 100-foot 10-gauge cord for larger appliances or power equipment that require up to 15 amps of power.