Wire and Cable Markings Reference
Read common U.S. conductor and cable jacket markings, compare THHN, THWN-2, XHHW-2, NM-B, and UF-B, and check manufacturer use conditions.
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Marking lookup
Read the whole jacket or conductor legend. A product may carry several designations, and those combined markings determine which listed uses are available.
| Marking | What it identifies | What to check |
|---|---|---|
| THHN | Thermoplastic, high-heat-resistant, nylon-covered conductor | The THHN designation alone is a dry-location designation; read all additional ratings. |
| THWN | Thermoplastic, heat- and water-resistant, nylon-covered conductor | A wet-location designation, commonly 75°C wet/dry for the marked product. |
| THWN-2 | THWN conductor with a 90°C wet/dry rating | Do not infer a 90°C termination rating from the insulation marking. |
| THHN/THWN-2 | One conductor carrying both designations | Use the rating for the actual environment and termination conditions. |
| XHHW-2 | Cross-linked, high-heat- and water-resistant conductor | The -2 designation supports 90°C wet/dry use for the listed product. |
| NM-B | Nonmetallic-sheathed cable | Common dry-location building cable; not a wet-location or direct-burial permission. |
| UF-B | Underground feeder and branch-circuit cable | Verify product listing for wet-location/direct-burial use and installation requirements. |
| MC | Metal-clad cable | The sheath name alone does not establish wet-location suitability or the grounding path. |
| AWG / kcmil | Conductor size designation | Size is not an ampacity rating; material and installation conditions still matter. |
| CU / AL / ALUMINUM | Conductor material identification | Match terminals, connectors, preparation, and instructions to the actual material. |
| 600 V / other voltage marking | Listed voltage rating | Not the operating voltage of the installed circuit. |
| SUN RES / sunlight resistant | An additional exposure rating | Not automatically a wet-location or direct-burial rating. |
| Manufacturer / listing mark / file | Product identification and traceability | Use these details to retrieve the exact product specification. |
Read a complete marking
In a marking such as 12 AWG CU THHN/THWN-2 600 V, the parts identify a conductor size, copper material, two insulation/use designations, and a voltage rating. They do not identify a circuit breaker rating or prove the conductor is suitable for every location.
Read repeated markings along the actual product rather than identifying cable by jacket color alone. Record the manufacturer, full type designation, size, material, voltage, temperature ratings, and any additional exposure markings before consulting the product sheet.
A -2 suffix is part of a particular type designation, not a general rule that can be attached to any cable abbreviation. Likewise, the letter B in NM-B does not make NM cable suitable for a wet location.
Check the product conditions
- Identify the environment: dry, damp, wet, sunlight, burial, or another specific exposure.
- Check the actual listing and product instructions for that exposure. A raceway outdoors or underground does not automatically make the conductors inside it a dry-location installation.
- Check conductor temperature, termination temperature, current-carrying conductor count, ambient conditions, and applicable wiring rules separately.
- Use the selected cable’s real dimensions when checking raceway fill. Insulation type, stranding, and manufacturer construction can change outside diameter.
Manufacturer product sheets are the authority for a particular stock number. This lookup explains selected common markings; it does not cover every flexible cord, specialty cable, or hazardous-location assembly.
Continue with the AWG area chart, conductor color reference, or existing ampacity tool. For NM installation rules, use the existing NM cable reference.
For a feeder comparison, the feeder-sizing tool checks its stated ampacity and voltage-drop inputs. Carry the identified conductor material and conditions into that task; a cable type marking alone is not a feeder-sizing result.