HAIK ELECTRIC · PROFESSIONAL REFERENCE
Electrical Wire Types & Uses
Identify common American conductors and cables by construction, intended use and location rating. Compare 12 types and read the limitations before selecting a wiring method.
Read the printed marking
Example: 12 AWG CU THHN/THWN-2 600 V. The marking identifies size, conductor metal, insulation designations and rated voltage. A cable marking such as 12/2 with ground typically describes two insulated 12 AWG conductors plus a grounding conductor.
THHN and THWN-2 ratings are not interchangeable: the complete dual marking matters. A wet-rated conductor is not automatically a direct-burial conductor, and a sunlight-resistant jacket is a separate property.
Copper and aluminum: connection matters
| Check | Copper | Aluminum |
|---|---|---|
| Terminal compatibility | Use a terminal identified for copper. | Use a terminal identified for aluminum and the actual conductor size. |
| Mixed-metal splices | Use a connector specifically listed for the combination. Follow its preparation and installation instructions. | |
| Tightening | Follow the marked torque and manufacturer instructions. Apply oxide inhibitor only when required or permitted by those instructions. | |
| Selection | Determine size using ampacity, load, voltage drop, terminal temperature and installation conditions. | |
Insulation temperature is not usable ampacity
NM-B and UF-B have a 60°C ampacity limit even though their conductor insulation is rated 90°C. Terminal ratings and correction or adjustment factors can further limit conductor ampacity. The wire size calculator provides a separate starting point for load and voltage-drop checks.
This guide describes common product families, not permission for a specific installation. Confirm the complete product listing, locally adopted electrical code, cable support, physical protection and environmental requirements. Underground raceways require suitable wet-location conductors.
Southwire building-wire selector · NFPA 70 — National Electrical Code
Product images show representative examples from the linked suppliers and manufacturers. Conductor sizes, counts and colors vary by product; always check the printed markings. Reference reviewed October 2026.