Toss any extension cord that feels stiff or looks crusty.

Yes—internal corrosion is often invisible, but a few clues give it away.

The biggest tell is the cord itself. If the insulation feels brittle, crunchy, or unusually stiff when you bend it, moisture has likely gotten inside the copper strands. Rust doesn’t show on the outside plastic, but the metal underneath corrodes and expands, making the cable hard to flex. Another sign: any green or white crusty powder near the plugs or along the cord is copper corrosion product—that’s bad news.

Plug it in and wiggle the cord near the connector while feeling for warmth or flickering—intermittent power means the strands are breaking inside. If you smell anything like burning dust or ozone, unplug it immediately and throw it away.

Damp basements are death sentences for extension cords. Future you deserves a thirty‑dollar replacement, not a fire.