| THW-2: |
Thermoplastic Insulation (usually PVC), Heat Resistant (90°C rating), suitable for Wet locations.
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| THWN-2: |
Same as THW except Nylon jacket over reduced insulation thickness. Also rated THHN.
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| THHN: |
Thermoplastic Insulation (usually PVC), High Heat Resistant (90°C rating), dry locations only, Nylon jacket. Also rated THWN.
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| TFFN: |
Thermoplastic Insulation (usually PVC), Flexible Fixture wire, Nylon jacket. Also rated MTW and AWM.
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| TFN: |
Thermoplastic Insulation (usually PVC), Fixture wire, Nylon jacket. Also rated AWM.
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| XHHW-2: |
Cross-linked Polyethylene Insulation (X), High Heat Resistant (90°:C rating), for Wet and Dry locations.
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| RHH: |
Rubber Insulation, High Heat Resistant (90°C rating) for dry locations only.
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| RHW-2: |
Rubber Insulation, Heat Resistant (90°C), Suitable for Wet locations.
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| 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.
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| MTW: |
Machine Tool Wire. Usually thermoplastic insulation (PVC) or thermoplastic insulation with nylon jacket. Most MTW is rated 60°C.
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| AWM: |
Appliance Wiring Material. Usually thermoplastic insulation (PVC) or thermoplastic insulation with nylon jacket. Most stranded copper type THHN in AWG sizes 14 through 6 is usually rated AWM. AS AWM, the product carries a 105°C rating.
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| 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 310.15 and 334.80, National Electrical Code 2008 edition). Thermoplastic (PVC) conductor insulation-nylon jacketed, with overall PVC cable jacket.
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| 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 table 310.16, 2008 edition). Thermoplastic (PVC) conductor insulation-nylon jacketed, with overall PVC cable jacket.
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| 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).
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| 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.
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