How to Identify Solid, Stranded and Compact Conductors

What it is

• Solid: one round wire. Common in small branch circuit sizes.
• Concentric stranded: layers of round strands twisted around a center strand. Building wire is usually Class B stranding under ASTM B8.
• Compressed stranded: concentric strands rolled slightly to close the gaps, giving a smaller diameter.
• Compact stranded: strands shaped and compressed so the conductor is nearly solid. It is noticeably smaller than standard stranded of the same size. ASTM B496 covers compact round copper.
• Flexible stranding uses many fine strands for cords and welding cable. See Copper Conductor Stranding Classes.

How to identify

1. Read the print legend. Some wire states the stranding or "compact."
2. Look at a fresh cut end.
3. Solid: one round face.
4. Concentric stranded: distinct round strands with visible gaps between them.
5. Compact: strands look flattened and fit together with almost no gaps. The cut face looks nearly solid with fine lines.
6. Compare diameters. Compact conductors are smaller than standard stranded of the same size.

Conductor types

Key points

• The conductor size (AWG or kcmil) is the same area whatever the stranding. Only the diameter changes.
• Compact conductors may need a different lug or connector, and a different crimp die. Check the lug marking and the maker's die chart.
• Fine-strand conductors in a screw terminal made for Class B strands can loosen. Use connectors listed for fine stranding.
• Building wire Class B stranding is commonly 7 strands for small sizes and 19 strands for larger sizes, rising with size.
• Ampacity is set by the NEC tables, not the stranding type.

Common mistakes

• Using a standard crimp die on a compact conductor.
• Sizing compact conductor by measured diameter and calling it one size smaller.
• Putting fine-strand welding cable in a standard mechanical lug.
• Twisting solid wire into a push-in connector not rated for it.

Governing standards: ASTM B8 (concentric-lay stranded copper); ASTM B496 (compact round concentric-lay copper); NEC 110.14 (terminations); lug maker's ratings.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.