Indoor vs Outdoor Extension Cord Rating
Jacket rating and wire gauge are two SEPARATE specs, and both matter. SJTW and SJOOW cords are rated for outdoor/wet-location use; a cord marked only SJT or SPT (no "W") is indoor-only, regardless of how thick its gauge is. A thick, high-amperage indoor-only cord left out in the rain is a genuinely different hazard from an undersized cord.
Reading the jacket code
Look for the printed code near the plug. A "W" suffix (SJTW, SJOOW, SJEOW) means outdoor/wet-location rated. SJOOW adds oil-resistant jacket and insulation ("OO") on top of that, useful in workshop or industrial environments with oil/grease/chemical exposure. Without the "W," the cord is indoor-only, no matter its gauge.
Why this matters as much as gauge
Our Cord Gauge Ampacity Index answers "is this gauge safe for this amperage at this length" — a completely separate question from "is this cord safe to use outdoors or in wet conditions at all." Both checks are required before using any cord outdoors.
This page is general reference, not an electrical code determination.
Frequently Asked Questions
Both are outdoor/wet-location rated, but SJOOW has an oil-resistant jacket and oil-resistant insulation (the extra 'O's), making it better suited to workshop, industrial, or job-site environments with oil/grease/chemical exposure. SJTW is the standard outdoor-rated cord for general yard, garden, and job-site use.
They answer different questions and both matter. Gauge determines safe amperage at your length; jacket rating (SJTW, SJOOW, etc.) determines whether the cord is safe to use outdoors or in wet conditions at all. A thick, high-amperage cord that's rated indoor-only is still unsafe left out in the rain.
No — jacket rating isn't about duration, it's about the insulation and jacket material's resistance to moisture and UV. An indoor-only cord's insulation is not built to the same moisture-sealing and UV-resistance standard as SJTW/SJOOW, regardless of how briefly it's exposed.
Check the jacket printing near the plug — SJTW, SJOOW, SJEOW, and similar 'W'-suffixed codes indicate outdoor/wet-location rating. A cord printed only 'SJT' or 'SPT' without a W is indoor-only.