The 'W' in SJTW stands for weather.

Check the printing on the jacket — if the code ends with a ‘W’ (like SJTW or SJOW), it’s rated for outdoor use.

These codes are standardized. The letters tell you the jacket material and intended environment. SJTW means junior hard service, thermoplastic, weather-resistant. SJOW is similar but with oil resistance added. Any cord that ends with ‘W’ is designed to handle moisture, sunlight, and temperature swings.

If the code doesn’t have a ‘W’ (like just SJT or SVT), that cord is indoor only. Don’t run a regular indoor cord outside — the insulation degrades fast, and water can get in.

Don’t guess. The jacket tells you everything.