Solid vs. Stranded Conductors:
Stranding is an important aspect of cable construction to consider. Some cables are available in both solid and stranded forms, but, generally, smaller cables are solid while larger cables (usually larger than 6 AWG) tend to be stranded. For those occasions when you have the option to choose or in the case that you just want to understand the construction of your cable a little better, these are the differences between solid and stranded conductors:
Solid - Solid conductors consist of just one strand of metal. They are easier to terminate than stranded conductors. They are also mechanically tough and inexpensive. The major disadvantage of solid conductors is their lack of flexibility
Stranded - Stranded conductors are composed of multiple metal strands bunched together in any number of configurations (discussed below in “Types of Stranding”). They are much more flexible than solid conductors, and the higher the strand count, the more flexible they are. While this can add some cost, it is essential for any wire or cable that will need to withstand any kind of movement or flexing.
Types of Stranding:
If a cable with a stranded conductor seems the appropriate choice for your application, you must then consider the type of stranding. While most constructions are specified by regulatory agencies, it is helpful to know some basic information about each type.
Bunched - Strands are gathered together with no particular design or arrangement. This is the least expensive type of stranding as it involves the least time and labor. Bunched stranding provides great flexibility.
Concentric - Strands are arranged in a circular pattern. Each layer alternates direction and has an increasing lay length (the center strand is longest). Concentric stranding is characterized by its mechanical strength and crush resistance.
Unilay - Strands are arranged in a circular pattern, but all layers are twisted in the same direction and share the same lay length. A unilay arrangement is light weight and allows for a small diameter.
Rope Lay - Strands are arranged into cabled groups. Each group usually consists of 7, 13, 19, or 27 strands as those can be gathered into a circular configuration easily. Rope lay is the most flexible type of stranding and is generally found in cables size 10 AWG and larger.
Equilay - Strands are similar to those in concentric stranding, but lay length is the same for each layer.
Bunched, unilay, and concentric are the most common types of stranding.
