Copper Stranding 101

August 30th, 2017 - One of the most important parts of cable is the stranding. For many of us, this important piece of hardware is unclear and can be confusing. Let us break it down simply…

COPPER COATING

Bare copper is preferred in most situations, though some copper alloys are better suited in environments where excellent abrasion or corrosion resistance is needed. More commonly, copper strands have a coating applied to add the properties required for a given application. For example, tin coating would be a preferred method when soldering is being used. The nickel plate and silver plate come into play when a higher temperature material is being used, such as a fluoropolymer. The nickel and silver melt and reflow at a higher rate.

COPPER CONSTRUCTION AND CONFIGURATION

Copper stranding is defined by both its overall size and an individual strand’s size. For example, a .75 mm2 construction would be defined as 32 ends of .2 mm. The .75mm2 would be the overall size, and then there are 32 strands of .2mm for each strand. Application often determines the size of stranding that will be needed. In a power application, the ampacity requirements for the stranding will define the size needed to handle the power load, considering all of the conductors that are in play.

STRANDING DESIGNS

Stranding configuration selection depends on the end-application of the cable and the environment in which the cable must perform. Key deciding factors are flex and movement requirements. The typical rule of thumb is “the more strands, the more flexible and the longer the lifespan”. From a movement and motion standpoint, a rope lay construction is by far the most flexible configuration – it is also by far the most expensive, highlighting the trade-offs buyers and engineers must constantly consider when choosing materials. For static applications, stranding matters less. Dramatic temperature fluctuation does not affect copper as much as movement does, but it is important to consider the connection point and how the cable will be terminated, as this could be a vulnerable area. Other factors to consider are applicable regulatory agency requirements. As a North American company, Northwire adheres to many guidelines, with UL as one of the most predominant. UL requires twisted stranding in most applications. With other approvals and some agencies, manufacturers can run stranding without twisting it together.