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The differences between indoor & outdoor extension cords

Updated February 21, 2017

Powering an electrical device that does not have a cord long enough to reach an outlet is the purpose of an extension cord. But an indoor extension cord is much different from an outdoor extension cord. An outdoor extension cord can be used indoors, but never use an indoor extension cord for outdoor use. Knowing the difference between the two types of extension cords will eliminate safety hazards.

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The main difference between indoor and outdoor extension cords is the insulation used to construct the different types of cords. Indoor extension cords do not have the same materials and protective insulation surrounding the wires as do outdoor extension cords. Outdoor extension cords have more durable insulation to protect the cords from moisture and outdoor temperature changes. Sunlight can break down the insulation used for indoor extension cords, but outdoor extension cords use material to protect the insulation from sunlight damage. Outdoor extension cords are also constructed to prevent damage from chemicals, such as oil, but indoor extension cords are not.


The gauge of an extension cord is the size or diameter of the conducting wires on the inside of the cord. Indoor extension cords do not have the same gauge of wires as outdoor extension cords do. The primary reason is that indoor extension cords rarely come in lengths longer than 25 feet, while outdoor extension cords come in lengths up to 150 feet or more. Larger-gauge conducting wire allows more current to flow through the extension cord, which is required at greater lengths and for different pieces of equipment.

Plug Type

Another difference between indoor and outdoor extension cords is the plug type used. Most indoor extension cords have a two-prong plug, and outdoor extension cords come with a three-prong plug. The third prong on the extension cord is a grounding wire that reduces the chance of electrical shock or even fires. The two-prong extension cord is generally used on lamps or small appliances found inside the home. The three-prong plug is only used with an outlet that has a ground slot. Combining a three-prong-plug extension cord with a two-prong-plug extension cord can be hazardous.


Every household appliance utilises different amperage to operate. The indoor extension cord generally has a lower amperage rating than an outdoor extension cord because outdoor devices utilise more amps than an indoor appliance. Home Depot states that a lamp utilises approximately .5 amps, while an outdoor device, such as a leaf blower, requires an extension cord that can allow up to 12 amps, which most indoor extension cords cannot accommodate.

Selecting Cords

Before purchasing an extension cord, you need to take several factors into consideration, including the environment the extension cord will be utilised in and the power requirements. The indoor extension cord is generally used for small electrical devices such as household appliances, lamps or computer equipment, while the outdoor extension cord is used for greater lengths and higher amperage and voltage requirements, and requires protection from the environmental conditions. All extension cords come with information about length, amperage ratings, voltage ratings and whether the cord is for indoor use, outdoor use, or can be used both indoors and outdoors.

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About the Author

Mitchell Brock has been writing since 1980. His work includes media relations and copywriting technical manuals for Johnson & Johnson, HSBC, FOX and Phillip Morris. Brock graduated from the University of Southern California in 1980, earning a Bachelor of Arts in English.

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