Stranded vs Solid Wire — When to Use Each

Stranded wire is many thin strands twisted together into a single conductor. Solid wire is one continuous round conductor. Both are permitted by NEC; the choice depends on gauge, flexibility needs, and terminal compatibility.

NEC code references

• NEC 110.14: Conductors must be compatible with terminations.
• NEC 310.106(C): Sizes 8 AWG and larger must be stranded if used in a raceway (some exceptions).
• NEC 310.106(D): Stranded conductors must remain stranded — combining strands at a single terminal lug is permitted if the lug is listed for it.

When solid is standard

• 14 AWG, 12 AWG branch circuits in dwellings: Solid is the dominant SKU for NM-B (Romex) and for THHN sold as branch wire. Receptacles, switches, and back-wire push-in connectors are designed for solid.
• Grounding electrode conductor (GEC): Solid copper is typical (smaller GEC sizes) for direct attachment to ground rods.
• Single conductors in short whips to junction boxes: Solid is fine for short, immobile runs.

When stranded is standard

• 8 AWG and larger feeders: NEC 310.106(C) and manufacturer terminal listings push stranded for ease of handling.
• Inside flexible conduit (FMC, LFMC): Solid can fatigue at bends; stranded handles flex better.
• Welding circuits, motor leads, control cables: Always stranded for repeated flex.
• Industrial machine wiring: Per NEC Article 670 — stranded conductors with proper ferrules.
• Long pulls through multiple bends: Stranded resists nicks during the pull better than solid.

Terminal compatibility

Most issues arise at terminations. Common rules:

• Receptacles / switches: Marked CO/ALR (copper/aluminum/rev), CU, or AL. Some accept both solid and stranded; some don't. Check the listing.
• Wire nuts: Solid + solid is easy. Stranded + stranded needs the right twist. Solid + stranded is fine if the stranded goes in first.
• Set-screw lugs: Compatible with both. Tighten to manufacturer torque spec.
• Compression connectors: Match the conductor type (solid vs stranded ferrule).

Fill is the same

NEC Chapter 9 Table 5 doesn't differentiate stranded vs solid:

So your wire fill chart numbers don't change.

Quick reference

• Solid: 14–12 AWG branch wiring, single short whips, GEC, immobile fixed installs
• Stranded: 10 AWG up (for flex), 8 AWG and larger (required by listing), motor circuits, control wiring
• Same fill math: identical Table 5 area regardless of stranding
• Verify terminal listing for any device accepting your conductor