PVC Conduit: Schedule 40 vs. 80
Schedule 40 PVC conduit is cheaper and has a larger inside diameter, so it's easier to pull wires through it. The plastic on Schedule 80 is thicker, but the conduit has the same outside diameter as 40, so the inside diameter is smaller. Always install Schedule 80 conduit in high-traffic areas or any other areas where it could get damaged, like behind a woodpile. The fittings (such as adapters and turns) are the same for Schedule 40 and 80.
Use THHN With PVC Conduit
THHN (thermoplastic high heat-resistant nylon-coated) is the best wire for pulling through PVC conduit. Other types of wire have a sticky rubber sheathing that makes them almost impossible to pull. Stranded THHN is used on most commercial jobs—it's more flexible than solid wire, which makes it easier to pull, and it doesn't spring back when you push it into the electrical box.