Recommended Practice For Cableways Selection and Installation

Cableway

The term cableways 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. This technical article covers the following topics //

• Selection of materials and shapes
• Design recommendations
• Metal and non-metal cableways are available
• Implementation of cableways

Selection of materials and shapes

Selection of materials and their shape depends on the following criteria //

• Severity of the electromagnetic (EM) environment along cableways (proximity of sources of conducted or radiated EM disturbances)
• Authorised level of conducted and radiated emissions
• Type of cables (shielded?, twisted?, optical fibre?)
• EMI withstand capacity of the equipment connected to the wiring system
• Other environmental constraints (chemical, mechanical, climatic, re, etc.)
• Future extensions planned for the wiring system

Non-metal cableways are suitable in the following cases //

• A continuous, low-level EM environment
• A wiring system with a low emission level
• Situations where metal cableways should be avoided (chemical environment)
• Systems using optical fibres

For metal cableways, it is the shape (at, U-shape, tube, etc.) rather than the cross-sectional area that determines the characteristic impedance.

Closed shapes are better than open shapes because they reduce common-mode coupling. Cableways often have slots for cable straps. The smaller the better. The types of slots causing the fewest problems are those cut parallel and at some distance from the cables.
Slots cut perpendicular to the cables are not recommended (see Figure 1).

In certain cases, a poor cableway in EMI terms may be suitable if the EM environment is low, if shielded cables or optical bres are employed, or separate cableways are used for the different types of cables (power, data processing, etc.).

It is a good idea to reserve space inside the cableway for a given quantity of additional cables.

The height of the cables must be lower than the partitions of the cableway as shown below. Covers also improve the EMC performance of cableways. In U-shaped cableways, the magnetic field decreases in the two corners.The picture below explains why deep cableways are preferable (see

Different types of cables (power and low-level cables) should not be installed in the same bundle or in the same cableway. Cableways should never be filled to more than half capacity!!

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