Cables and busways

From Electrical Installation Guide

Two types of distribution are possible:

  • By insulated wires and cables
  • By busbar trunking (busways)

Distribution by insulated conductors and cables


  • Conductor


A conductor comprises a single metallic core with or without an insulating envelope.

  • Cable


A cable is made up of a number of conductors, electrically separated, but joined mechanically, generally enclosed in a protective flexible sheath.

  • Cableway


The term cableway refers to conductors and/or cables together with the means of support and protection, etc. for example : cable trays, ladders, ducts, trenches, and so on… are all “cableways”.

Conductor marking

Conductor identification must always respect the following three rules:

  • Rule 1
The double colour green and yellow is strictly reserved for the PE and PEN protection conductors.
  • Rule 2
    • When a circuit comprises a neutral conductor, it must be light blue or marked “1” for cables with more than five conductors
    • When a circuit does not have a neutral conductor, the light blue conductor may be used as a phase conductor if it is part of a cable
    • with more than one conductor
  • Rule 3
    • Phase conductors may be any colour except:
    • Green and yellow
    • Green
    • Yellow
    • Light blue (see rule 2)

Conductors in a cable are identified either by their colour or by numbers (see Fig. E41).

Fig. E41 – Conductor identification according to the type of circuit
Number of conductors in circuit Circuit Fixed cableways
Insulated conductors Rigid and flexible multi-conductor cables
Ph Ph Pn N PE Ph Ph Ph N PE
1 Protection or earth G/Y
2 Single-phase between phases R3 R3 BL LB
Single-phase between phase and neutral R3 LB BL LB
Single-phase between phase and neutral + protection conductor R3 G/Y BL G/Y
3 Three-phase without neutral R3 R3 R3 BL B LB
2 phases + neutral R3 R3 LB BL B LB
2 phases + protection conductor R3 R3 G/Y BL LB G/Y
Single-phase between phase and neutral + protection conductor R3 LB G/Y BL LB G/Y
4 Three-phase with neutral R3 R3 R3 LB BL B BL LB
Three-phase with neutral + protection conductor R3 R3 R3 G/Y BL B LB G/Y
2 phases + neutral + protection conductor R3 R3 LB G/Y BL B LB G/Y
Three-phase with PEN conductor R3 R3 R3 G/Y BL B LB G/Y
5 Three-phase + neutral + protection conductor R3 R3 R3 LB G/Y BL B BL LB G/Y
> 5 Protection conductor: G/Y - Other conductors: BL: with numbering

The number "1" is reserved for the neutral conductor if it exists

  • G/Y: Green and yellow
  • BL: Black
  • R3: As indicated in rule 3
  • LB: Light blue
  • B: Brown

Note: If the circuit includes a protection conductor and if the available cable does not have a green and yellow conductor, the protection conductor may be:

  • A separate green and yellow conductor
  • The blue conductor if the circuit does not have a neutral conductor
  • A black conductor if the circuit has a neutral conductor

In the last two cases, the conductor used must be marked by green and yellow bands or markings at the ends and on all visible lengths of the conductor.

Equipment power cords are marked similar to multi-conductor cables (see Fig. E42).

Fig. E42 – Conductor identification on a circuit breaker with a phase and a neutral

Distribution and installation methods

(see Fig. E43)

Distribution takes place via cableways that carry single insulated conductors or cables and include a fixing system and mechanical protection.

Fig. E43 – Radial distribution using cables in a hotel

Busbar trunking (busways)

Busways, also referred to as busbar trunking systems, stand out for their ease of installation, flexibility and number of possible connection points

Busbar trunking is intended to distribute power (from 20 A to 5000 A) and lighting (in this application, the busbar trunking may play a dual role of supplying electrical power and physically holding the lights).

Busbar trunking system components

A busbar trunking system comprises a set of conductors protected by an enclosure (see Fig. E44).

Used for the transmission and distribution of electrical power, busbar trunking systems have all the necessary features for fitting: connectors, straights, angles, fixings, etc. The tap-off points placed at regular intervals make power available at every point in the installation.

Fig. E44 – Busbar trunking system design for distribution of currents from 25 to 4000 A

The various types of busbar trunking:

Busbar trunking systems are present at every level in electrical distribution: from the link between the transformer and the low voltage switch switchboard (MLVS) to the distribution of power sockets and lighting to offices, or power distribution to workshops.

Fig. E45 – Radial distribution using busways

We talk about a distributed network architecture.

There are essentially three categories of busways.

  • Transformer to MLVS busbar trunking
Installation of the busway may be considered as permanent and will most likely never be modified. There are no tap-off points.
Frequently used for short runs, it is almost always used for ratings above 1,600 /2,000 A, i.e. when the use of parallel cables makes installation impossible. Busways are also used between the MLVS and downstream distribution switchboards.
The characteristics of main-distribution busways authorize operational currents from1,000 to 5,000 A and short-circuit withstands up to 150 kA.
  • Sub-distribution busbar trunking with low or high tap-off densities
Downstream of main-distribution busbar trunking , two types of applications must be supplied:
  • Mid-sized premises (industrial workshops with injection presses and metalwork machines or large supermarkets with heavy loads).
  • The short-circuit and current levels can be fairly high (respectively 20 to 70 kA and 100 to 1,000 A)
  • Small sites (workshops with machine-tools, textile factories with small machines,supermarkets with small loads). The short-circuit and current levels are lower (respectively 10 to 40 kA and 40 to 400 A)
Sub-distribution using busbar trunking meets user needs in terms of:
  • Modifications and upgrades given the high number of tap-off points
  • Dependability and continuity of service because tap-off units can be connected under energized conditions in complete safety
The sub-distribution concept is also valid for vertical distribution in the form of 100 to 5,000 A risers in tall buildings.
  • Lighting distribution busbar trunking
Lighting circuits can be distributed using two types of busbar trunking according to whether the lighting fixtures are suspended from the busbar trunking or not.
  • busbar trunking designed for the suspension of lighting fixtures
These busways supply and support light fixtures (industrial reflectors, discharge lamps, etc.). They are used in industrial buildings, supermarkets, department stores and warehouses. The busbar trunkings are very rigid and are designed for one or two 25 A or 40 A circuits. They have tap-off outlets every 0.5 to 1 m.
  • busbar trunking not designed for the suspension of lighting fixtures
Similar to prefabricated cable systems, these busways are used to supply all types of lighting fixtures secured to the building structure. They are used in commercial buildings (offices, shops, restaurants, hotels, etc.), especially in false ceilings. The busbar trunking is flexible and designed for one 20 A circuit. It has tap-off outlets every 1.2 m to 3 m.

Busbar trunking systems are suited to the requirements of a large number of buildings.

  • Industrial buildings: garages, workshops, farm buildings, logistic centers, etc.
  • Commercial areas: stores, shopping malls, supermarkets, hotels, etc.
  • Tertiary buildings: offices, schools, hospitals, sports rooms, cruise liners, etc.


Busbar trunking systems must meet all rules stated in IEC 61439-6.

This defines the manufacturing arrangements to be complied with in the design of busbar trunking systems (e.g.: temperature rise characteristics, short-circuit withstand, mechanical strength, etc.) as well as test methods to check them.

The new standard IEC61439-6 describes in particular the design verifications and routine verifications required to ensure compliance.

By assembling the system components on the site according to the assembly instructions, the contractor benefits from conformity with the standard.

The advantages of busbar trunking systems


  • Easy to change configuration (on-site modification to change production line configuration or extend production areas).
  • Reusing components (components are kept intact): when an installation is subject to major modifications, the busbar trunking is easy to dismantle and reuse.
  • Power availability throughout the installation (possibility of having a tap-off point every meter).
  • Wide choice of tap-off units.


  • Design can be carried out independently from the distribution and layout of current consumers.
  • Performances are independent of implementation: the use of cables requires a lot of derating coefficients.
  • Clear distribution layout
  • Reduction of fitting time: the trunking system allows fitting times to be reduced by up to 50% compared with a traditional cable installation.
  • Manufacturer’s guarantee.
  • Controlled execution times: the trunking system concept guarantees that there are no unexpected surprises when fitting. The fitting time is clearly known in advance and a quick solution can be provided to any problems on site with this adaptable and scalable equipment.
  • Easy to implement: modular components that are easy to handle, simple and quick to connect.


  • Reliability guaranteed by being factory-built
  • Fool-proof units
  • Sequential assembly of straight components and tap-off units making it impossible to make any mistakes

Continuity of service

  • The large number of tap-off points makes it easy to supply power to any new current consumer. Connecting and disconnecting is quick and can be carried out in complete safety even when energized. These two operations (adding or modifying) take place without having to stop operations.
  • Quick and easy fault location since current consumers are near to the line
  • Maintenance is non existent or greatly reduced

Major contribution to sustainable development

  • Busbar trunking systems allow circuits to be combined. Compared with a traditional cable distribution system, consumption of raw materials for insulators is divided by 4 due to the busbar trunking distributed network concept (see Fig. E46).
  • Reusable device and all of its components are fully recyclable.
  • Does not contain PVC and does not generate toxic gases or waste.
  • Reduction of risks due to exposure to electromagnetic fields.
Fig. E46 – Example of a set of 14 x 25A loads distributed along 34 meters (for busway, Canalis KS 250A)

Functional features for Canalis

Busbar trunking systems are getting even better. Among the features we can mention:

  • Increased performance with a IP55 protection index and ratings of 160 A through to 1000 A (Ks).
  • Lighting offers with pre-cabled lights and light ducts.
  • Fixing accessories. Quick fixing system, cable ducts, shared support with “VDI” (voice, data, images) circuits.

Busbar trunking systems are perfectly integrated with the environment:

  • white color to enhance the working environment, naturally integrated in a range of electrical distribution products.
  • conformity with European regulations on reducing hazardous materials (RoHS).

Examples of Canalis busbar trunking systems

Fig. E47 – Rigid busbar trunking able to support light fittings: Canalis KBA or KBB (25 and 40 A)
Fig. E48 – A busway for medium power distribution: Canalis KN (40 up to 160 A)
Fig. E49 – A busway for medium power distribution: Canalis KS (100 up to 1000 A)
Fig. E50 – A busway for high power distribution: Canalis KT (800 up to 5000 A)