WF-16/U field phone wire, which is officially named "CABLE, TELEPHONE, WF-16()/U", consists of two pairs of parallel-stranded insulated conductors for use in 4-wire telephone circuits. Each pair is insulated with high density polyethylene. One pair is colored olive drab and has two ridges to allow it to be identified by touch in the dark. The other pair is brown, and lacks the ridges. Visually, WF-16/U wire looks like two lengths of "zip cord" or "lamp cord", loosely twisted together.
Key characteristics include:
- Conductors each consist of 7 strands of bare, hard-drawn copper alloy #85 wire, each with a diameter of 0.0085±0.0001 inches.
- Insulation is high-density linear polyethylene, containing 1%-3% titanium dioxide ultraviolet inhibitor. Minimum wall thickness at any point is 0.014 inches.
- Dimensions of each pair are:
- Major axis: 0.125±0.008 inches
- Minor axis: 0.083±0.005 inches
- Conductor separation: 0.038±0.005 inches
- Weight per mile: 62 pounds
- Characteristic impedance for DNVT signaling: 132Ω
- Standard unit of product: One mile +2%/-0% wound on reel DR-5, with both ends accessible.