No matter how many wall outlets you have in your home, chances are there aren’t enough (especially if you've got an older house) and you’re going to need an extension cord or two.
And that opens you up to a certain amount of danger. Using the wrong extension cords—or old, damaged cords—can cause fires, damage your tools and equipment, and potentially even kill you—there are an estimated 2,200 shock-related injuries involving extension cords every year.
Choosing the correct extension cord for your needs is a necessary step if you want to avoid injury and property damage. There are four things to consider when choosing an extension cord.
First, you need to make sure you’re using the right extension cord for the environment you’ll be working in—are you going to use it indoors or outdoors? In oily conditions (like a mechanics’ shop)? When buying an extension cord this information will typically be printed clearly on the packaging. but if you bought your cord a while back and can’t remember, there is a code printed on every extension cord that tells you all you need to know:
“S” = general use
“W” = weather resistant, outdoor use
“O” = oil resistant
“FT2” = flame retardant
You’ll find many other codes, but for most household projects these are the ones you need to know.
Next, you need to make sure you’re using the correct gauge of extension cord. Every extension cord has an American Wire Gauge (AWG) rating that describes how thick the wire is inside the insulation. Lower AWG actually indicates larger gauge; most extension cords range from 16-gauge (smallest) to 10-gauge (largest) in two-gauge increments—you can find larger or smaller cords, but they’re not common.
The gauge determines how much power the cord can handle, measured in amps. Sixteen-gauge cords are suitable for light duty, 10-gauge cords are intended for tools and appliances that pull a lot of power. If in doubt, use a higher-gauge cord—it’s sometimes recommended that the 14-gauge is the smallest extension cord you should use, because it’s rated for 15 amps, which matches the typical breaker in your home’s electrical cabinet. That means your breaker will trip before the extension cord is overwhelmed and overheated.
Speaking of amps, choosing the right gauge of extension cord requires knowing how much power you need to pull through it. The appliance or tool you’re powering will tell you how much power it needs measured either in watts or amps; if it’s watts, you can easily calculate the amps it needs by dividing by 120 volts (the standard residential voltage; if you know you’re on a different voltage, divide by that).
Once you know the amps you need the extension cord to handle, select the proper gauge:
16 AWG = 10 Amps
14 AWG = 15 Amps
12 AWG = 20 Amps
10 AWG = 30 Amps
Again, if you’re uncertain, a larger gauge cord is better than an undersized one.
Finally, you need to know how long your extension cord needs to be. Electricity encounters resistance when it flows, and the farther it has to travel, the more resistance it meets, reducing how much power actually arrives at your tools or appliances. It’s always a good idea to get an extension cord that’s exactly as long as you need.
If you need to run a very long (50-100 foot) extension cord, consider going up in gauge to compensate for the distance.
