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Use the right extension cord

power—the amount of energy used in a second, measured in watts

1 horsepower = 746 watts.

The gauge of wire in an extension cord must be compatible with the amount of current the cord will be expected to carry. The amount of current depends on the equipment plugged into the extension cord. Current ratings (how much current a device needs to operate) are often printed on the nameplate. If a power rating is given, it is neces- sary to divide the power rating in watts by the voltage to find the cur- rent rating. For example, a 1,000-watt heater plugged into a 120-volt circuit will need almost 10 amps of current. Let’s look at another example: A 1-horsepower electric motor uses electrical energy at the rate of almost 750 watts, so it will need a minimum of about 7 amps of current on a 120-volt circuit. But, electric motors need additional current as they startup or if they stall, requiring up to 200% of the nameplate current rating. Therefore, the motor would need 14 amps.

Add to find the total current needed to operate all the appliances supplied by the cord. Choose a wire gauge that can handle the total current.

American Wire Gauge (AWG)

Wire size

#10 AWG #12 AWG #14 AWG #16 AWG

Handles up to 30 amps

25 amps 18 amps 13 amps

Remember: The larger the gauge number, the smaller the wire!

Do not use extension cords that are too long for the size of wire.

The length of the extension cord also needs to be considered when selecting the wire gauge. Voltage drops over the length of a cord. If a cord is too long, the voltage drop can be enough to damage equip- ment. Many electric motors only operate safely in a narrow range of voltages and will not work properly at voltages different than the voltage listed on the nameplate. Even though light bulbs operate (somewhat dimmer) at lowered voltages, do not assume electric motors will work correctly at less-than-required voltages. Also, when electric motors start or operate under load, they require more current. The larger the gauge of the wire, the longer a cord can be without causing a voltage drop that could damage tools and equipment.

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Section 7

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