How to choose an extension cord: gauge, length and outdoor ratings

An undersized extension cord can overheat and starve your tools of power. Choosing the right one means matching its gauge and amp rating to what you're plugging in, for the length you need.

Gauge: lower numbers are thicker

Wire thickness is measured in American Wire Gauge (AWG). The lower the number, the thicker the wire and the more current it can safely carry.

• 16 gauge: light duty. Lamps, fans, string lights, small tools.
• 14 gauge: medium duty. Many power tools, lawn equipment, shop vacuums.
• 12 gauge: heavy duty. Saws and high-draw tools, especially over longer runs.
• 10 gauge: extra heavy duty.

Length matters

Longer cords lose more voltage along the way, so they need thicker wire for the same tool. Retailer charts commonly show 16-gauge cords rated around 10 to 13 amps depending on length, 14-gauge around 13 to 15 amps, and 12-gauge around 15 amps even at 100 feet.

The most reliable step: check the amp rating printed on the cord or package, and make sure it's at least the amps listed on your tool's label. And use the shortest cord that reaches.

Reading the jacket

Letters printed on the cord jacket describe its construction:

• S: service cord (designed for hard service)
• J: junior service (lighter-duty insulation)
• T: thermoplastic jacket
• W: rated for outdoor use

A cord marked SJTW, for example, is a junior service thermoplastic cord rated for outdoor use. If you'll use it outdoors, look for the W.

Also look for a certification mark from a recognized testing lab, such as UL or ETL.

Plugs and features

• Three-prong (grounded) cords for tools with three-prong plugs. Never cut off the ground pin.
• Lighted ends show the cord is live.
• Multiple outlets at the end are handy for lights, but watch the total load.
• Built-in GFCI protection is helpful outdoors and near water.
• Cold-weather flexible jackets stay easier to handle in winter.

What not to do

• Don't plug space heaters and other high-draw heating appliances into extension cords; many manufacturers say to plug directly into a wall outlet.
• Don't daisy-chain extension cords together.
• Don't run cords under rugs or through doorways where they can be pinched.
• Don't use a cord that's damaged, feels hot, or has a missing ground pin.
• Don't use extension cords as permanent wiring.

Questions people ask

What gauge extension cord do I need for a circular saw?

Check the saw's amp rating. Many circular saws draw around 15 amps, which calls for a heavy-duty cord, often 12 gauge, especially at longer lengths.

Can I use an indoor cord outside?

No. Use cords rated for outdoor use (marked with a W), which have jackets designed to resist moisture and sunlight.

Why is my extension cord getting warm?

It may be undersized for the load, coiled while in use, or damaged. Stop using it and switch to a heavier-gauge cord rated for your device.