Replace the entire extension cord.

Don’t splice it. Extension cords are not designed to be repaired safely by the average person, and the risk of fire or shock isn’t worth saving twenty bucks.

The problem with splicing is that any break in the insulation or improper connection creates a weak point. Heat builds up, moisture gets in, and eventually you get a short or a fire. Even if you use heat shrink and a proper crimp, you’re still trusting your repair to handle the same current load as the original cable. Most people don’t have the tools or know-how to do that right.

Buy a new cord. They’re cheap. If the damage is near the plug, you can sometimes replace just the plug end (male or female) with a replacement cap sold at hardware stores. That’s a different story—it’s a standardized connection designed to be replaced. But for a cut in the middle of the cable? Toss it.

This is not where you save six bucks.