| 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),
Flexible 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: |
Underground
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. |