General information about cables and busbars

Cables and busbars: Cables

Cable designation and cable classes

A key design feature of a cable is its flexibility. This is primarily determined by the number of cores inside the cable.

Cable classes as defined by IEC 60228:


Class 1 - cable with solid conductor

Class 2 - cable with stranded conductors

Class 5 - cable with finely stranded conductors

Class 6 - cable with a large number of extra finely stranded conductors

The conductors in class 1 and 2 cables are inflexible conductors, either solid or stranded. These are used predominantly in applications with low-curvature bending radii and in fixed or inflexible installations.
The flexible conductors of classes 5 and 6 are suitable for high-curvature cable bending radii.

The cable conductors used in low-voltage power distribution installations mainly belong to classes 1, 2, 5 and 6.

Cables with solid conductors in class 1 used for these applications normally have a cross section of 16 mm² or less.

Please note: Solid-conductor cables in classes 1 and 2 are smaller in diameter than cables in classes 5 and 6 even when their cross sectional area is the same. As a result, cables with the same diameter from different classes may have different connection cross sections.


Solid and stranded sector-shaped conductors are also used.


Cable lugs and wire-end ferrules

Cables are connected by means of lugs and wire-end ferrules to the molded case circuit breaker in order to provide stable, safe connections. These elements help to make solid connections at the breaker.

The cable is first stripped over the distance L before the cable lug or wire-end ferrule is attached to the cable.


The cable must be stripped carefully to ensure that the correct amount of insulating material is removed. If too much material is removed, it will not be possible to make a secure connection between the cable and cable lug or wire-end ferrule.

Compression cable lugs compliant with DIN 46235 have ideal heat transfer characteristics for connecting busbar connectors. By contrast, "Tubular cable lugs with narrow palm for switching devices" (designation "SG" for example) must be used to make direct cable connections in the termination area of the molded case circuit breaker. These cable lugs vary in design depending on make. All cable lugs of this kind with the dimensions stipulated in standard IEC 609437‑1, Annex P are basically suitable.

Cables and busbars: Busbars

In addition to cables, the busbar is also widely used in electrical connections, especially in cubicles.

Some of the reasons for using busbars include:

  • High-curvature bending radii which are unsuitable for cables of large cross section

  • Lack of space

  • Heat dissipation, air circulation

Rigid and in some cases flexible busbars are used in the examples of applications listed above.


Rigid busbars are made of copper or aluminum. Pre-punched aluminum busbars, some of which are threaded, are often used.

Flexible busbars are chosen for applications which demand a high degree of flexibility and high-curvature bending radii. These consist of bundles of copper or aluminum strips.