Stranded copper ropes
The term strand indicates a collection of wires wrapped around each other to create a sort of spiral. This structure is mostly used to create wires in the electrical cable sector, where strands allows for various solutions to be produced.
A stranded cable is generally made up as follows: in the very centre there is the strand, i.e. the wires twisted together that act as electrical conductors. For these, hard-drawn copper or tin-, silver- or nickel-plated copper is usually used to provide greater resistance to oxidation, or aluminium.
The conductor is then protected by a layer of insulation, which is generally made from thermoplastic materials, and fillers are added between the two to fill the gaps between the core and the sleeve. Equally important is the guard, which is a coating made from a conductive material that is applied to the insulation or cores to restrict the electric field and protect it from electromagnetic disturbances.
As mentioned, the conductor can consist of a single rigid wire or several wires that will form the strand and, depending on how many there are, it will determine how flexible the cable will be. This is a fundamental point because it is the flexibility that determines the class of the strand, as established in standard IEC 60228.
When it comes to electrical cables, there are four classes of flexibility, which increase as the number of internal wires increases:
- Class 1: solid conductors, ideal for permanent installations;
- Class 2: stranded conductors designed for fixed installation;
- Class 5: flexible conductors, preferred in cases of vibration, bending or reduced range of movement;
- Class 6: very flexible conductors.
Advantages of a stranded cable
Choosing a stranded cable is often advisable when you need a softer and more flexible cable that can adapt to systems and applications involving bends or small spaces.
In fact, the interlaced strands make it much easier to bend the cable during laying without the risk of damaging it, which is why they are often used in circuits, robotics and cabling work, while solid cable is preferred in cases where the cable is exposed to corrosive elements or the action of atmospheric agents, such as in telecommunications and construction.
Other advantages of stranded cables include greater resistance to vibration (although the terminations of these cables are more fragile than solid cables). One final interesting advantage of stranded cable is its cost-effectiveness over the long term, even though the initial cost might be higher than for solid conductor cables.
Stranded cable: fields of application
As we have seen, the main advantage of stranded cable is that it is very flexible, especially class 5 and class 6 cables. This characteristic means that stranded cable can be laid much more easily in situations where the general conditions do not allow for a more rigid cable to be used appropriately.
When there are small spaces or bends in the system involved, you can therefore choose a solution that offers high flexibility. A typical case is in domestic appliances, where where choosing a multi-core cable also provides greater overall resistance and less power dissipation. With fixed installations, a class 2 stranded cable could be sufficient but if you need more flexibility, it is better to opt for one of the higher classes.
