Non-Metallic Sheathed Cables, the most common product under the heading of Building Wire, is known as NMD90 and NMWU. These cables have a rating of 300 volts.

The power conductors are insulated with PVC or XLPE. NMD90 Nylon cables then have a nylon protective covering extruded over the PVC insulation. Many years ago the insulated conductors were each wrapped in paper, assembled with a bare ground wire, then enclosed in a fibrous braid, finished with an asphalt compound, or alternatively enclosed in a PVC jacket. The PVC/Nylon, or XLPE insulation, instead of the paper wrapping, has characteristics such as to allow a reduction in the bulk, reducing the overall size of the cable by about 50%. As well as the advantage of reduced size, the stripping time is much less without paper, improving ease and speed of installation.

Both NMD90 and NMWU, may have two insulated conductors (with ground) laid parallel (Figure 3), or three insulated copper conductors cabled together (Figure 4) with a bare copper solid or stranded bonding (grounding) conductor. Copper conductor sizes #14 AWG to #10 AWG are solid, while sizes #8 AWG to #2 AWG are stranded. The overall covering is a PVC jacket which is extruded over the cabled core.

Applications for NMD90 cables are exposed or concealed wiring in dry or damp locations, where not exposed to mechanical injury. NMWU cables, which have a much greater thickness of insulation, are suitable for most NMD applications, and also for exposed or concealed wiring in damp or wet locations, and for direct earth burial providing that protection is provided as required by the inspection authority.