As one person indicated, if using traditional lamp wire, one side is ribbed and the other is smooth. Ribbed is the neutral (negative) side and smooth is the line (positive).

Is the ribbed wire hot?

The wire with the ribbing or stripe is the neutral wire, and the other one is hot. If you don’t see any markings on the wires, and the plug has two prongs of equal size, the cord is not polarized.

Is Hot wire smooth or ribbed?

The hot wire is always smooth on the outside of the cord, while the neutral wire is ribbed on the outside. For flat cords with polarized plugs on the end, the larger prong (or terminal) is the neutral wire.