Wire Design

Making the Perfect Cable

wire design

There are five fundamental constituents that make a cable: conductor, insulation, shield, filler and strength member. The conductor carries the power or signal to its desired location. The insulation isolates the conductor from adjacent electrical paths. The shield protects the conductor signal integrity from RFI, EMI and EMP sources. The filler is used to make the cable round by filling the voids of the imperfect wire packing. The strength member, when terminated properly, gives the cable a significant increase in axial strength.Extrusion geometry, material composition, weave pattern, plating and various exotic operations can modify the cable to perform better in specific applications all having advantages and disadvantages that accompany. Identifying a balance between these components and appropriate end use is no easy feat and usually requires an experienced engineer to guide through the process.

Conductor

Starting with the design of the conductor; three main geometries exist: solid, stranded and tinsel. The material composition of the conductor can be exotic as the imagination, but some common examples are: cadmium, phosphor bronze, chromium, steel, aluminum, platinum, silver and of course copper. The most commonly selected conductor is copper due to its conductivity/cost factor. Silver has the highest electrical conductivity of all metals and it is also less susceptible to corrosion. Unfortunately silver costs more than copper and therefore is less commonly used as a homogenous conductor. Plating offers a more cost effective solution to using precious metals. A copper cable can be plated with tin, gold, silver or nickel to keep the advantages such as conductivity, corrosion resistance and strength of particular precious metals. Other metals can be treated the same way, but copper is the most common candidate for plating.

wire design

Primary Insulation

Primary insulation surrounds the conductor to protect signal integrity from adjacent electrical paths. Primary insulation can be made of various thicknesses depending upon the allowable internal cable space and the required conductor isolation. Material composition may vary depending upon the environment it will be subject to and desired electrical characteristics.

wire design

Jacket Insulation

Jacket insulations are usually limited to PVC, polyurethane, thermo-plastic elastomer (TPE), silicone rubber, polyester and fluoropolymers (PFA, FEP and ETFE) depending upon the end use application (See table under primary insulation for general polymer characteristics). Outer jacket insulations can be combined by twisting jackets together, molding a divider strip or adding a zip jacket to combine them.

Shield

Three main types of shield weave patterns are: braided, spiral and foil. Materials commonly used are copper, tin-plated copper, silver-plated copper, nickel-plated copper, high and low permeable irons, carbon fibers, tinsel wire and aluminum. The characterization, like anything in this summary, depends upon the particulars, but below is a generalization of shielding characteristics.

wire design

Filler & Strength Member

Filler material does as the name suggests, it fills the wire. Filler material can make the cross-sectional geometry into a desired shape, typically round. Strength members are included into cable construction when the conductor is subject to axial loads that it is unable to withstand. Tinsel wire is a common wire that usually requires strength members.

wire design