Can you use an indoor extension cord outside?

No. Use an extension cord outdoors only if it’s marked for outdoor use, with a W in the letters on its jacket (such as SJTW) or the words “Acceptable for use with outdoor appliances”.

Why an indoor cord stays inside

The safety standard for extension cords, UL 817, requires cords for outdoor use to be jacketed: two or three insulated wires inside an extra jacket of insulation. The jacket protects the wires from weather. An unjacketed cord used outdoors can be damaged until the wires inside are exposed, a risk of shock and fire.

The W on an outdoor cord is its weather rating. It stands for a jacket that resists water, damp and sunlight, around wires rated for wet locations.

How to tell an outdoor cord

• A W in the letters printed along the jacket, such as SJTW or SJOOW.
• Some makers print OUTDOOR too: a Carol cord reads like 16/3 SJTW OUTDOOR.
• The marking “Acceptable for use with outdoor appliances; store indoors while not in use.” on the cord.

No W and no outdoor marking means the cord stays indoors. To decode every letter, see what the letters on an extension cord mean.

Using an outdoor cord outside

• Plug it into a GFCI-protected outlet, or use a portable GFCI or an extension cord with a GFCI built in.
• Keep plugs and connections off the ground and dry. Watertight or sealable connectors help.
• Don’t run it through a doorway.
• Use one cord long enough for the job. The warning tag on extension cords says “Do not plug one extension cord into another.”
• Unplug it when you’re done and store it indoors.

For the gauge a load and length need, see the extension cord gauge chart. For holiday lights, the lights need an outdoor marking too: see indoor vs outdoor Christmas lights.

Replace a cord with cuts, cracks or worn insulation. Never tape it up and keep using it.