Wire comes in two basic constructions: solid (a single conductor) and stranded (multiple thin wires twisted together). Both have the same AWG size designation but different physical properties and ideal uses.
A single solid conductor of the full cross-sectional area.
Multiple thin wire strands twisted together to form the conductor.
| Property | Solid | Stranded |
|---|---|---|
| Flexibility | Low — stiff | High — very flexible |
| DC Resistance | Slightly lower | Slightly higher |
| Skin Effect | Same at 60 Hz | Same (only Litz wire, with individually insulated strands, reduces it) |
| Fatigue Resistance | Low — will break if flexed | High — designed for movement |
| Outer Diameter | Smaller | Larger (same gauge) |
| Cost | Lower | Higher |
| Termination | Push-in, screw terminals | Crimp, solder, or ferrule |
| NEC Residential | Standard (14-10 AWG) | Required in raceways (NEC 310.3(C)) |
For residential in-wall wiring (14, 12, and 10 AWG), solid wire is standard and preferred. For anything that moves or flexes, and for 8 AWG and larger in a raceway (NEC 310.3(C)), stranded wire is the right choice. The ampacity rating is the same for both — NEC Table 310.16 applies regardless of whether the conductor is solid or stranded.
Solid wire for in-wall wiring (NM-B Romex, conduit runs under 10 AWG). Stranded wire for flexible applications: appliance cords, conduit runs in 8 AWG and larger, panel wiring, and any installation requiring flexing or vibration resistance. NEC does not specify one over the other for most applications.
Neither is universally better. Solid wire is easier to terminate in devices (outlets, switches, breakers) and slightly less expensive. Stranded wire is more flexible and less prone to breakage from repeated bending. For conduit pulls in 8 AWG and larger, stranded is strongly preferred.
Yes, solid and stranded wire can be connected with wire nuts (use nuts rated for stranded), push-in connectors (use clamp-type, not back-stab), or listed wire connectors. Avoid back-stab (push-in) outlets and switches for stranded wire — they are rated for solid wire only.
NM-B (Romex) cable uses solid conductors in 14 AWG, 12 AWG, and 10 AWG sizes — the most common sizes for residential branch circuit wiring. NM-B is not available in stranded; for flexible runs, use THHN stranded conductors in conduit or SOOW/SJO flexible cord for appliances.