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Extension Cords

Buying Guides: Extension Cords
 
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 - Location, usage and jacket type.
Plug Type - 3-prong, 2-prong and specialty plugs.
Power Rating - Maximum current, wire gauge, and length
 

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 cord
 
Outdoor extension cords fall into three broad categories, indicating general capabilities:
 

Occasional use cords are suitable for smaller projects and tools.

Frequent use cords can handle larger tools and equipment and heavier use.

Rugged cords are designed for continual use on job sites, even in extreme weather, and are suitable
  for high-amperage tools.


 
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.
 
Jacket Designation Chart
 

Plug Type


Most extension cords have either two-prong plugs or three-prong plugs. It's important to select a plug type that works with the devices you will connect to the cord.
 

• 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.


 
2-3 prong plug type
 
 

• 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.
        

Power Rating


Maximum Amperage


It's important to select an extension cord that can handle the energy requirements of any connected devices.
 

• Every extension cord has a maximum amperage, which is the upper limit on the electrical current it
  can conduct safely.

• If you connect a device that uses a current level above this limit, the device may not function correctly
  and the cord may overheat.


 
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 device.

• If you plan to connect multiple devices to the cord at the same time, add up the current requirements for
  each device.


 
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 cord.

• 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 conductions inside.
 
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.
 
Cord with AWG number printed on the jacket
 
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.
 
Minimum Wire Gauge
 

Features


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 apart.
 
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