4 Things to Know About Extension Cord Insulation Ratings

The temperature rating printed on an extension cord is the maximum heat the insulation can handle before it softens, cracks, or melts. Ignoring it can start a fire.

Ambient heat from the environment adds to the heat generated by electricity flowing through the wire. If the combined temperature exceeds the rating, the insulation fails.

Cheap indoor cords are often rated 60°C, which is fine for a lamp but dangerous on a sun-baked patio. Surface temperatures can hit 60°C before you even plug anything in.

For any cord that might see heat—garage, workshop, or outdoors in summer—get one rated at least 90°C. SJTW or SJTOW cords usually meet that requirement.