To the casual observer all electrical wire looks very much alike, but the reality is that, beneath the layers of insulation, most wires fall into one of two main categories – stranded or solid – each of which has its own distinct advantages and disadvantages.
Solid wire, also known as single-strand wire or solid-core wire, consists of a single piece of metal wire. Stranded wire is created when a number of thin individual wires are wrapped or bundled together. Choosing the type of wire most suited to a particular project is usually a case of comparing the pros and cons of stranded v solid wire to see which one best meets a particular specification.
Solid wire is much less flexible than stranded wire. In applications that require the wire to move around, such as in a cable for a computer mouse or a connection in a robotic arm, stranded wire is used, as the repeated strain on a piece of solid wire can cause metal fatigue which will eventually cause the wire to break.
If an application requires little or no movement, such as using a wire to make a connection on a circuit board, then the preference is to use solid wire, as it is much easier to use in these sort of situations. While a solid wire requires only a single point of connection, the individuals strands of stranded wire can sometimes separate in this kind of application, potentially leading to a short circuit.
The greater the number of individual strands a piece of wire contains, the more flexible, break-resistant and stronger the wire is. For example, extension cords are made of stranded rather than solid wire, as this allows them to be bent or twisted on a regular basis without causing excessive stress on the wires inside. However, the more strands a wire contains, the higher the cost.
The minimum number of strands used in most applications is six. In this kind of wire, there will be once central strand surrounded by six others. Surrounding these seven strands with a complete circle of additional strands usually requires a further 12 lengths of wire, leading to a total of 19 strands. Other common values are 37 and 49, but as the diameter of a wire increases, the number of strands becomes less exact and varies from one piece of wire to another.
Wire with at least 49 strands is usually the minimum requirement for applications needing significant amounts of movement, whereas applications that require constant movement, such as the wires that connect a set of headphones to an audio jack, will usually utilise between 70 and 100 strands.
As well as being more flexible than a solid wire of the same thickness, stranded wire is a more effective conductor of electricity, as the total surface area of the individual wires is greater than that of a single piece of solid wire.
The overall diameter of a length of stranded wire is larger than that of a length of similarly sized length of solid wire, as an allowance needs to be made for air trapped between the strands and the fact that more insulation is needed to provide full protection. This size difference may make stranded wire impractical for some applications.
Although all wires will transmit electricity effectively and can be used for both commercial and residential applications, an electrician will first determine the appropriate gauge of wire to use and then decide on the type of metal before considering the advantages of stranded v solid wire.
Stranded wire may be more flexible and far more durable when it comes to vibration, but it generally has a larger diameter and costs more to manufacture. This is especially the case when it comes to wire with a very large number of strands.
Solid wire is better suited to applications that require a high level of protection against corrosion. For this reason, outdoor applications where there is a possibility that wire may be exposed to the elements or corrosive materials, such as the connections within a car engine, are better served with solid rather than stranded wire.
In order to reduce the additional diameter of stranded wire – a factor which may make it unsuitable for some applications – it is possible during the manufacturing process to compact or compress stranded wire before the insulation layer is applied.
This compression process requires the wires to be cold-formed in order to reduce the diameter of the individual strands to as little as possible. The air is then squeezed out of the spaces between the strands. Separation between the strands needs to be maintained, however, if the length of stranded wire is to retain its flexibility and durability.
This additional processing means that stranded wire is significantly costlier to manufacture than solid wire. Other considerations include various electromagnetic effects, which can either reduce the amount of power a length of wire can carry or lead to greater levels of electrical interference. The nature of these effects vary depending on whether stranded or solid wire is used.
Although it may be tempting to use solid wire to save money in a particular project or application, the fact that solid wire can prove to be less durable means that the potential cost of replacing all the wiring needs to be factored in. In many cases, the use of solid wire may turn out to be a false economy, and stranded wire could prove to be far more cost-effective in the long run.