| THW-2 | Thermoplastic Insulation (usually PVC), Heat Resistant (90°C rating), suitable for Wet locations. |
| THWN-2 | Same as THW except Nylon jacket over reduced insulation thickness. Also rated THHN. |
| THHN | Thermoplastic Insulation (usually PVC), High Heat Resistant (90°C rating), dry locations only, Nylon jacket. Also rated THWN. |
| TFFN | Thermoplastic Insulation (usually PVC), Fixture wire, Nylon jacket. Also rated MTW and AWM. |
| TFN | Thermoplastic Insulation (usually PVC), Fixture wire, Nylon jacket. Also rated AWM. |
| XHHW-2 | Cross-linked Polyethylene Insulation (X) High Heat Resistant (90°C rating) for Wet and dry locations. |
| RHH | Rubber Insulation (we actually use cross-linked polyethylene because it qualifies for rubber), High Heat Resistant (90°C rating) for dry locations only. |
| RHW-2 | Rubber Insulation (again, cross-linked polyethylene is used by most manufacturers), Heat Resistant (90°C), Suitable for Wet locations. |
| USE-2 | Underground Service Entrance. Most utilize cross-linked polyethylene insulation rated for 90°C in direct burial applications. Product is usually triple rated RHH—RHW—2-USE-2. |
| MTW | Machine Tool Wire. Usually thermoplastic insulation (PVC) or thermoplastic insulation with nylon jacket. Most MTW is rated 60°C. Southwire's copper type THHN is also rated MTW. |
| AWM | Appliance Wiring Material. Usually thermoplastic insulation (PVC) or thermoplastic insulation with nylon jacket. Southwire's stranded copper type THHN in AWG sizes 14 through 6 is also rated AWM. As AWM, the product carries a 105°C rating. |
NM-B | Nonmetallic-Sheathed Cable. The "B" denotes that individual conductor insulation is rated 90°C; however, ampacity is limited to that for a 60°C conductor (see NEC Section 336-26, 1999 edition). Thermoplastic (PVC) conductor insulation-nylon jacketed, with overall PVC cable jacket. |
| UF-B | Undergound Feeder. The "B" denotes that individual conductor insulation is rated 90°C; however, ampacity is limited to that for a 60°C conductor (see NEC Section 339-3(a)(4), 1999 edition.) Thermoplastic (PVC) conductor insulation-nylon jacketed, with overall PVC cable jacket. |
| SEU | Service Entrance Cable, Unarmored. Usually type XHHW insulated conductors with overall PVC jacket. As such, the cable is rated for 90°C dry, 75°C wet locations. Another school of thought is the "U" in the designation denotes the shape of the cable (if you look at the end, it resembles a closed "U" shape). |
| SER | Service Entrance Cable, Round. Same construction material-wise as SEU, but round construction affords use of more than 3 conductors to which SEU is limited |
* Note: All information is provided courtesy of Southwire.
