Why is copper used in electrical wiring

Lines and cables

Cables and wires are the basis of every electrical circuit. Without them, a physical connection of the components would not be possible. In order to adapt the cables and wires to the intended use, one must consider several important aspects. The correct selection of the specific type, the conductor color and a suitable cross-section.

First of all, the difference between the two terms cables and wires should be discussed. Cables are also called lines. Some people say cables to what is laid in the ground and wires to what is used above the ground. The term cable is often used when referring to cables with special protection (special sheath).

In practice, these terms become blurred. Cables and wires are used to transport energy and data (signals) with the help of electrical current.

The head

The conductor of a cable can be made of different materials:

  • Copper (most common)
  • Aluminum (less often)
  • Silver (very rare)
  • POF (P.lastic Optical F.iber)
  • GOF (Glet Optical F.iber)

Most often, copper is used because of its comparatively very good electrical conductivity.

Aluminum has only around 2/3 of the electrical conductivity of copper, which means that with the same length and resistance, an aluminum wire, in contrast to copper wire, requires about 1.5 times the cross-section. However, the specific weight of aluminum is only around 1/3 that of copper. Thus, in all applications where there are no space problems for the thicker electrical aluminum conductors, but weight plays an important role, aluminum is the better choice over copper. Typically, this is the case, for example, in the area of ​​overhead lines.

Silver has the highest electrical conductivity of all metals, but for cost reasons it is only used in special cases, such as in the field of high-frequency technology, as a thin coating over a copper cable.

In addition to copper wires, optical conductors are also used in communication networks. In short-distance data transmission in particular, POF is an alternative to glass fiber (GOF), currently the most technically important fiber optic cable.

 

Furthermore, one differentiates between conductors according to their structure. There are Solid conductor as Stranded conductor:

  • Solid conductor consist of a solid strand of the material used, such as copper. They become solid up to about 16 mm2 produced. You are only for fixed installation authorized.

  • Stranded conductor consist of up to several hundreds of extremely fine conductors that are combined in a network.

Solid cables can hardly be bent compared to stranded cables. The bending radius must be very large here so that the individual wire does not break. If the conductor cross-section remains the same, the more strands (= individual small cores) there are, the easier it is to bend a stranded wire. This means that the maximum permissible bending radius is also smaller. With a stranded conductor that is bent with a radius smaller than the bending radius, individual strands can break. The minimum bending radius for flexible cables is z. B. 3 x d (three times the diameter).

The standardization DIN EN 60228 (VDE 0295) specifies four classes of conductors: single-wire, multi-wire, fine-wire and extra-fine wire. The former is the solid conductor described above.

 

The isolation

The insulation is an electrically non-conductive protective layer around the conductor. The combination of conductor and insulation is called Vein. The process in which the insulation is applied is called Extrusion. Only after the conductor has been insulated can the current-carrying wire be touched without receiving an electric shock. This is what DIN VDE requires Protection against direct contact guaranteed. In the past, conductors were wrapped in paper and soaked in pitch, wax, or oil.

About 100 years ago rubber was discovered as an insulation material, because rubber is a much better insulator than paper. A few years later, plastics were discovered as insulation material, which quickly went into mass production and can therefore be manufactured quickly and cheaply.

Nowadays common plastics are PE (polyethylene), PP (polypropylene), PVC (polyvinyl chloride), PUR (polyurethane) and many more. These plastics offer better protection against external environmental influences such as moisture and dirt. PVC is the most widely used plastic because it is cheap and flame retardant.

 

The screen

The screen offers protection against immissions and emissions. This is particularly important for data lines, because every current-carrying conductor generates magnetic fields that penetrate the insulation and influence other conductors through induction. For this reason, a screen must be used for data lines in order to prevent any loss of data. The type of screen is always adapted to the intended use, because a compromise has to be found between flexibility and adequate protection. This means that a copper pipe around the wires would offer complete protection, but it would not be flexible to lay.

Nowadays, electromagnetic compatibility, or EMC for short, is becoming more and more important. The systems are more and more networked and therefore more susceptible to interference caused by magnetic fields. Good shielding offers adequate protection against this.

The shielding usually consists of a wire mesh around the core, or a foil that is wrapped around the core.

Immission control
The screen protects the data that is transported on the wire from external electromagnetic influences.
Application: cables from the frequency converter to the motor

 

Emission protection
The screen prevents electromagnetic interference from being emitted through the core.
Application: Cables for the transport of analog signals or in data transmission

 


 

The outer jacket

Cables and lines must be selected in such a way that they correspond to the mechanical, chemical and thermal influences. The adaptation of the outer jacket to the demands is made by selecting the correct jacket material. Mechanical demands are, for example, bending, tension or impact. Chemical loads can arise, for example, through contact with acids, oils or even coolants.

There are also thermal requirements for the outer jacket. In some areas of application, temperatures of -50 ° C to 1400 ° C prevail, which cables and wires have to withstand.

Sunlight poses an additional difficulty in the selection of the sheath materials, because UV radiation can cause the sheath to become brittle and thus damage it, as adequate protection against mechanical stress can no longer be guaranteed. In addition, the outer jacket must meet the requirements of fire protection regulations.

Further information on lines and cables can be found in the 'Lapp Cable Guide', which can be downloaded or opened as a PDF document.