How is an electrical cable manufactured?
wire drawing, wire wrapping, extrusion, shielding

The different manufacturing processes that an electrical cable goes through can vary greatly depending on the type of cable involved. For example, a H07V-U cable goes through three different processes while a 37x1.5 screened braided cable undergoes no fewer than eight different processes. We can generally categorise a cable's production process into four main stages: wire drawing, wire wrapping, extrusion and screening (shielding).

firstly, the wire wrapping process is carried out. This process consists of transforming Cu from its initial 8 mm diameter (the state in which the copper is received from our suppliers) to the required final diameter.

This diameter will depend on the formation of the conductor and the nominal section that is to be obtained. This process is carried out in the wire drawing machines. The wire drawn copper goes through a series of wire drawing machines to progressively reduce its diameter, until the wire is reduced to the required final diameter. All the wire drawing machines used incorporate diamond components to extend the working life of these machines: only diamonds, with their extraordinary strength, are capable of resisting the wear and tear produced by the copper as it comes into contact with the wire drawing machines.

Once the wire drawing process has been completed, the copper wire is annealed. The annealing process consists of recrystallising the copper after it has been hardened in the wire drawing process. This recrystallisation process is what gives the wire the electrical
and mechanical characteristics required for it to be used as a conductor. To achieve this, once it has been wire drawn in continuous lengths, the copper wire is heated by an electrical current and coated in a very weak emulsion of wire drawing oil. Finally, the wire is put through a drying process.

After the wire drawing process, the next step consists of wire wrapping. This process is made up of joining, in an orderly fashion or otherwise, different Cu wires, either bare or coated, to form a cable. If the joining is disorderly, this is known as double twist stranding.

If it is orderly, it is known as wire wrapping. The wire wrapping process is carried out in the wire twisting machines. There are different types of wire twisting machines, and these are used according to the assembly that is to be carried out. It is not the same to group a lot of small conductors together (rigid cabling) as it is to group together a few large conductors planetary cable stranding machines).

The third stage corresponds to extrusion. This consists of the application, in continuous lengths, of a thermoplastic or thermo stable covering. The extrusion press machine acts as a pump forcing the smelted material in its interior through a head, applying it on to the element that enters into the machine.

Depending on the cabling process phase, we can differentiate four types of extrusion processes, which are: insulation material extrusion, where a covering is applied with electrical characteristics on to the conductor; filling material extrusion, where the interstices that are between the conductors are covered; base material extrusion, which consists of applying a covering with mechanical characteristics before proceeding with shielding, with the purpose of separating and protecting the inside of the cable; and lastly, covering material extrusion, which consists of a covering whose characteristics depend on the working environment of the cable (presence of chemical agents, abrasive work, continuous bending of the cable, etc.). This is the last process that is applied to the cable before proceeding to the final tests and to the subsequent distribution and retail of the cable.

In the thermo stable rubber extrusion machines, once the covering has been applied, the cable is introduced into a continuous tube where, during a pre-set time, it is subject to pressure and temperature conditions under which the chemical vulcanisation process is
produced. This reaction results in the material remaining stable (without melting) at higher temperatures (thermo stable).

Lastly, the cable is encased in a metal covering, with the purpose of providing mechanical protection (shielding) or electrical protection (screening). In this phase, we can distinguish three types of process: firstly, flexing, in which one or two overlapping metal bands are applied to achieve total protection against rodents, external impacts or screening of the cable. These make the cable rigid and do not bear up to traction forces. In the second place, in the crown, a crown of metal wires is applied around the cable. If steel wires are used, a high level of protection for the cable is achieved, without excessive rigidity and which can withstand elevated traction forces. If the wires are copper, the effect is that of electrical screening, at the same time this gives a good electrical section to the metal protection.

Following the wire drawing, wire wrapping, extrusion and screening, comes an exhaustive
quality control procedure in the laboratory, guaranteeing that the cable is ready for retail.