NM-B 12/2 W/G 600 V
Nominal calculation, not one manufacturer's datasheet. The conductors are NEC Chapter 9 Table 8; the insulation, nylon and jacket walls and the ground are the values the makers print, because UL 719 was not read. Five makers' cables of the same name differ by up to 10 % in width: check the datasheet before you specify or order.
By NEC Table 8 and the makers' walls, NM-B 12/2 W/G 600 V comes to about 10.0 × 4.7 mm (width × thickness) and a weight of about 130 kg/km.
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Main dimensions
| Conductor | Copper 12 AWG (3.3 mm²), Ø 2.1 mm | NEC 2026 Chapter 9 Table 8: Class B concentric or solid diameter |
|---|---|---|
| Insulation | PVC 0.38 mm | NM-B conductor PVC insulation: the THHN / THWN-2 band of its size (Encore 15, 20, 30, 40 mil; Cerrowire the same sums; UL 719 not read) |
| Diameter over insulation | 2.8 mm | |
| Core diameter | 3.0 mm | |
| Width × thickness | 10.0 × 4.7 mm | |
| Weight (approximate) | 130 kg/km |
Layer by layer (inside out)
| # | Layer | Material | Thickness mm | Ø over mm | Source | How firmly |
|---|---|---|---|---|---|---|
| 1 | Insulation | PVC | 0.38 | 2.8 (on each core) | NM-B conductor PVC insulation: the THHN / THWN-2 band of its size (Encore 15, 20, 30, 40 mil; Cerrowire the same sums; UL 719 not read) | maker catalogue value, standard text not read |
| 2 | Nylon jacket (polyamide) | Nylon (PA) | 0.10 | 3.0 (on each core) | NM-B conductor nylon jacket: the THHN / THWN-2 band (Encore 4, 5, 6 mil; UL 719 not read) | maker catalogue value, standard text not read |
| 3 | Ground conductor: Separation tape | Paper | 0.10 | 2.3 | kraft paper wrap: makers name it, none prints its thickness; typical 0.1 mm | typical value, no rule |
| 4 | Separation tape | Paper | 0.10 | 3.2 | kraft paper wrap: makers name it, none prints its thickness; typical 0.1 mm | typical value, no rule |
| 5 | Sheath | PVC | 0.76 | 4.7 | NM-B PVC jacket 30 mil: Cerrowire, Encore; Southwire prints 25 mil on the flat 14 to 10 AWG cables (UL 719 not read) | maker catalogue value, standard text not read |
NM-B (Romex) is the UL 719 nonmetallic-sheathed cable of NEC Article 334: copper conductors in PVC and nylon (the THHN / THWN-2 walls), a bare ground in kraft paper, a paper separator and a PVC jacket. Two conductors lie flat, the ground between them; three conductors are flat to 10 AWG and round from 8 AWG, as most makers build them. Checked against Southwire, Cerrowire, Encore and HT Wire: research/designer-americas/nm-b.md in the site repository.
Materials in this cable: Copper, PVC
Weight, by part
| Conductors | 90 kg/km |
| Metal screens and armour | 0 kg/km |
| Insulation, semicon, tapes, fillers and sheaths | 40 kg/km |
| Total | 130 kg/km |
|---|
Each layer's cross-section times its density; stranded conductors, laid-up cores and helical wires count 2 % longer than the cable. Densities: copper 8.89 and aluminium 2.703 g/cm³ (the values of IEC 60028 and IEC 60889); XLPE 0.92, PE 0.94, PVC 1.45, semicon 1.12, steel 7.85 g/cm³ (usual compound values).