Extension cords play a critical role in delivering AC power from an outlet to a remote appliance that needs it. Though it’s important to note that not all extension cords are the same. Some have important features, and some are rated for indoor or outdoor use. Failing to heed these characteristics could lead to a serious safety hazard.

What Is An Indoor Extension Cord?

Indoor extension cords are meant for light-duty applications and low voltage. They are the sort of thing you might use to power a single strand of Christmas lights, a box fan, or perhaps a small household coffee maker.

What Is An Outdoor Extension Cord?

Outdoor extension cords are more robust and their indoor rated siblings. They are specifically made from thick gauge wire and are coated with a durable coating of rubber, plastic or vinyl. There are even a few heavy-duty outdoor extension cords that are rated for special situations where they can be used around flammable liquids, chemicals or in extreme temperatures.

Outdoor Extension Cord Categories

There are three general categories of extension cords. Picking the one that’s right for you may depend on the situation you are using it in.

Occasional Use outdoor extension cords are meant to be used to power electric power tools for a short period of time. This is something you might need to power a circular saw during a construction project. They aren’t really meant to convey power constantly for long-term use.

Frequent Use outdoor extension cords are designed to handle larger tools and equipment and heavier use. This is something you might use to power a 110 Volt table saw in your workshop.

Rugged outdoor extension cords are the most robust and are designed to be used at commercial job sites and to handle high-amperage power tools. They also tend to have superior weather resistance, which makes them a better choice for things like running a small campsite generator.

Understanding Outdoor Extension Cord Designations

If you look at the packages or tags on the cord you might see some letters denoting the characteristics and intended purpose of the outdoor extension cord.

  • S – Notes a general use extension cord that is flexible.
  • W – Notes that the extension cord is rated for outdoor use.
  • J – Designates that the extension cord has standard 300 voltage insulation in the coating. The lack of a J indicates that the cord has thicker, 600-volt insulation, for heavy use.
  • P – Is most often found in air conditioner power cords and household extension cords, that need to be wired in parallel.
  • T – Is displayed on an extension cord with a vinyl thermoplastic jacket.
  • E – Is displayed on an extension cord with a thermoplastic elastomer rubber jacket. This is sometimes written as TPE.
  • O – Notes that the extension cord is oil-resistant

What Are The Different Extension Cord Plug Types?

Just like how there are different types of extension cord characteristics the there are also different types of plugs that you might encounter.

Two-prong plugs are more common with light-duty interior extension cords. They are not as safe and should never be used for high voltage appliances.

Three-prong plug extension cords are the most common for outdoor use. The third prong essentially serves as a super ground for carrying high voltage. It greatly reduces the risk of electric fire caused by short circuits.

It does need to be plugged into a three-prong outlet to work properly. If you don’t have a three-prong outlet, or you are attempting to plug it into a two-prong extension cord, you should not attempt to alter the plug or remove the ground.

Does Gauge Affect Amperage Capacity?

Most outdoor extension cords have an AWG rating stamped on the jacket. This indicates the maximum amperage of current that it can convey from the outlet to the device before it starts overheating. Sometimes a cord can deliver a higher amperage than this rating, however resistance in the cord can cause it to gradually overheat, short circuit, fail or even start a dangerous electrical fire.

If you aren’t sure of the amperage of a device or power tool, you should check the stamped metal plate on the back or bottom. Most will have the amperage or wattage on the label or stated in the owner’s manual. If it only gives you the wattage, some simple math can be used to determine the amperage. You simply need to divide the number of watts by 110.

It’s also worth noting that the gauge of the extension cord and internal wire will influence the amount of amperage it can deliver. This is usually stamped on the plug or the wire’s jacket tag. If you see something like a 14/3 on the cord jacket it is indicating that the extension cord is made from 14-gauge wire and it also has three wires inside.

Does Length Affect Amperage Capacity?

The greater the distance that current needs to travel, the greater the resistance. This can impact the amount of current being delivered to the end device. In certain circumstances, it can also lead to heating throughout the length of the cord.

Ideally, you want to use a cord that is only as long as you need. If you only need to carry current for 20 feet, a 100-foot long extension cord might not be a good idea.

Special Extension Cord Features

There are some special features that you might find on certain extension cords.

  • A Green Coating on an extension cord has been tested and rated by UL for safety.
  • GFCI Extension cords have a built-in Ground Fault Circuit Interrupter which will automatically shut down power to the extension cord if there is a temporary short circuit. It acts very much like a built-in fuse.
  • A Lighted Plug indicates when the cord is powered.
  • A Connector Box fits around the extension cord plug and the plug on the intended electrical device. This helps keep them connected for times when you might need to pull the cord through a junction or lift the electrical device up a ladder.