Extension cords allow you to power a device when its own cable does not reach an electrical outlet. They expand the reach of your household electrical circuit and make it accessible for everything from holiday lights to heavy yard work. Understanding the differences between electrical extension cords can help ensure safe operation, energy efficiency and high tool performance. This buying guide will explain what to look for in an extension cord so you can feel confident you're selecting the cord that will work best for you.
Factors to Consider
Environment and Usage
The first thing to consider when selecting an extension cord is where you intend to use it. Cords are clearly labeled as "indoor" or "indoor/outdoor." Cords designed for outdoor use have more durable jackets, or covers, than cords intended only for indoor use. The jacket is the rubber, plastic or vinyl covering that insulates and protects a cord’s conducting wires.
Outdoor extension cords have jackets that offer protection from moisture, direct sunlight and abrasion. Some heavy duty cords are also rated for protection against oils, other chemicals or extreme temperatures. It's perfectly safe to use an outdoor extension cord inside, but using an indoor extension cord outside can lead to overheating and dangerous short circuits.
Outdoor extension cords fall into three broad categories, indicating general capabilities:
You can learn more about a cord’s durability and intended use by looking at
its specific jacket type, listed as letter designation on product packaging
and the cord itself.
Refer to the chart below to see what the letters in jacket designations mean.
Devices with two-prong plugs (like lamps or double insulated tools and appliances) can be used safely with either a two-prong or three-prong extension cord.
Devices with three-prong plugs should only be used with three-prong extension
cords. The third prong in the extension cord provides a path to the ground
wire in a household electrical circuit. This ground wire greatly reduces
the risk of electrical shocks and fires. The three-prong cord itself should
only be used with properly grounded three-slot outlets.
Extension cords with other plug configurations are available as well. For
example, in industry and construction, some equipment requires cords with
twist-lock plugs, which twist to lock into an outlet. Extension cords are also
available for the specialty receptacles and plugs used in RVs and RV parks.
If you have a device with an unfamiliar plug design, refer to this guide from the National Electrical Manufacturers Association (NEMA). Identify the plug type of your device and select an extension cord with a matching configuration. For safe operation, it's essential that you always match plugs to the correct outlet type.
The power requirements for household electrical devices vary widely. For
example, a typical table lamp requires only .5 amps, while a leaf blower might
use 12 amps. You can usually find the energy requirements for electrical
devices listed on the device itself, as well as in the instruction manual.
It's a good idea to identify the energy requirements of a device before
connecting it to an extension cord.
Many extension cords also have a listed power rating:
If the rating for the electrical device and the cord are both listed in amps,
simply select an extension cord that exceeds the amperage requirements of the
The power requirements for some devices are listed in watts, rather than amps.
In this case, use this formula to convert the rating to amps:
Amps = watts/110
|For example, to calculate the amperage of a 100-watt bulb, you would divide 100 by 110 to get .9 amps.|
Gauge and Length
If an extension cord doesn't include a maximum amperage rating, you can figure out its capacity by looking at its American Wire Gauge (AWG) rating:
Wire gauge is a measure of the diameter of the conducting wires inside the
Wires with a larger diameter can handle greater current.
Lower AWG number indicate a thicker wire and a higher current capacity, so the
lower the number, the higher the cord's capacity to deliver power.
Gauge is typically listed along with the number of conducting wires in the
cord. For example, a 14/3 cord contains 14-gauge wire, and has three
Typically, you can find a cord's gauge rating printed on the cord jacket. If you're replacing an old cord, look for the AWG number printed on the jacket, and select a new cord with the same gauge.
To determine the cord's capacity, it's important to consider the cord length along with the wire gauge. Every extra foot of cord increases the electrical resistance, which decreases the power the cord can deliver to connected devices. Because of this, it's best to use a cord that is only as long as you need. For example, it's inefficient to use a 100-foot cord to power a device that only needs to extend 40 feet from an outlet.
Refer to the chart below for minimum wire gauge recommendations for different devices and cord lengths.
Built-in Ground Fault Circuit Interrupter (GFCI): A device that
automatically shuts power to the extension cord in the event of a ground
fault, a type of short circuit that can result in dangerous shocks
Lighted Plug: A plug that lights up to indicate when the cord is powered
Connector Box: A device that fits around both the extension cord plug
and the plug on the connected electrical device to keep them from pulling
Locking Socket: A locking mechanism built into the extension cord
socket that keeps the device and cord securely connected
Multiple Sockets: Cords that allow you to power multiple devices at once
Safety Listing: A guarantee than an independent testing agency, such as Underwriters Laboratories (UL mark), Intertek (ETL mark) or the Canadian Standards Association (CSA mark) has ensured an extension cord is safe for its rated use. The Occupational Safety and Health Administration (OSHA) defines standards for safe extension cord use. You can learn about OSHA standards at http://www.osha.gov/SLTC/electrical/standards.html