Electrical cables, characteristics and dimensioning!

Present in our daily lives, cables are responsible for conducting electrical current through electrical circuits in the most varied types of electrical installations. There is a wide variety of electrical cables on the market, which are electrical conductors usually made of copper or aluminum, because of the low resistivity of these materials.

It is common for people to get confused when they think that electrical cables and wires are the same, but that they think so is wrong, because what differentiates electrical cables from wires   is the internal composition of each one, because the wires are formed by a single conductor, while cables are composed of several micro conductors (filaments), but which have the same purpose and characteristics as conducting electric current and offering low resistance to electric current. Let’s get to know the characteristics of the electric cables and wires and how to dimension the electric cables and wires. Come on!

Single filament and multipole filaments.

Cables and Wires

Electrical cables and wires are extremely important within electrical installations, as they are responsible for conducting electrical current safely and efficiently to the point of demand in electrical installations. Without these items, there would be no generation, transmission and distribution of electricity, that is, electric cables and wires are essential for electricity.

Electric cables and wires have the same purpose, as they are used to conduct electric current, but are manufactured in different ways. Internally, the conducting wires of electricity are manufactured with just one wire, so the wires have the characteristic of being rigid due to their constructive form, being known as solid cables.

Conductive electrical cables, in turn, are manufactured internally by several interlaced electrical conductive wires, which make them more flexible compared to solid cables. In the images below we will have a better perception of the difference between electrical cables and electrical wires :

Electric cable with multiple filaments.

Note that the cable, unlike the wire, has several filaments, so the cable is much more flexible. The wire, on the other hand, is rigid, not having the same flexibility as the cables. However, both are necessary, have different applications, advantages and disadvantages.

Electrical wires have a single filament.

How to dimension the cables?

Due to the need to maintain the safety of both the professional who works with electrical energy and the users of the installation, NBR5410 stipulates a series of measures that must be considered.

It is worth mentioning that the standard talks about power conductors, that is, the selection and installation of these conductors in electric lines are focused on power lines, therefore, they do not apply to control or instrumentation conductors.

With respect to power cables, all conductors must be provided with at least insulation, unless the use of bare conductors or provided only with cover is expressly permitted. Uni and multipole cables must meet the following standards:

  • Cables with EPR insulation, according to ABNT NBR 7286;
  • Cables with XLPE insulation, according to ABNT NBR 7287;
  • Cables with PVC insulation, to ABNT NBR 7288 or ABNT NBR 8661.

The standard stipulates through tables which conductors should be used taking into account several factors such as, for example, temperature, number of cables per conduit, types of insulation, installation methods, among many other factors.

The dimensioning of the cables must respect not only the installation needs, but also the standard that regulates electrical installations in Brazil.

Complications that may arise

A recurring problem in installations is how much it is necessary to make the splice of rigid wires with flexible wires, for that it is necessary to use splice gloves, or proper devices to avoid the bad count and heating of the amendments.

These wires are well applied in aerial networks, where it is necessary that the conductor has a high resistance, to prevent it from breaking between one pole and another, where there is the effort of the weight of the electric wire itself.

The wires are known in the market as solid or rigid wires, composed of only one conductor, these devices are still widely used in telephone applications and in abrasive areas, where the electrical conductor needs to be buried or subjected to high pressure.