The green wire is the ground wire, the white wire is the neutral wire, and the black wire is the hot wire. Light-duty interior extension cords often lack the ground wire, but if a ground wire is present, be sure to connect it.

The first prong goes into the neutral slot in a wall power outlet, while the second goes into the hot slot. Consequently, non-grounded plug cords have an increased risk of causing electrical shock and damage to appliances due to the lack of a grounding mechanism to function as a circuit breaker.

Plugs — Outdoor extension cords always have three-prong plugs, whereas indoor cords may have either two or three prongs, depending on particular needs. The third prong is connected to the cord's grounding wire, to reduce risk of electrical shock or fire.

Do not “daisy chain,” that is, plug surge protectors into extension cords or other surge protectors. This practice voids the NRTL listing and the manufacturer's warranty.