The basics of cable trays

Before a cable is laid on the route, a number of preparatory plans are required, which in practice are rarely implemented with the necessary care, but in some cases are not required by clients. Below are some hints and suggestions which can be implemented during the next construction measure:

1. At the beginning there is one (or more) technical system(s) to be wired. Here it is important that the planner or supplier develops the corresponding schematics as a planning concept. The required performance parameters, functional units and material parameters should be reflected in this.
2. If the functional units or technical systems are provided with the identification system used in the building, there is a clear basis for all the trades involved in the realization of interfaces right from the start.
3. The start and destination points should be integrated both in equipment location plans and later in the cable pull lists.
4. Now the most important work of a planner begins: The appropriate cable routes must be found and determined. Larger planning offices are now taking the path of 3D-supported route planning in order to identify collisions with other media (water or wastewater pipes, heating pipes, ventilation shafts, etc.) and also to meet the requirements, e.g. those of standard-compliant fireproofing, at an early stage. It is also possible to meet user requirements, e.g. for redundant cable routes.
5. For IT cabling, the planning task often consists exclusively of integrating appropriate route systems, usually as cable trays, into the planning, since the occupancy is either taken over by another company on behalf of the user or one would like to implement this by one's own operating personnel after completion. How large do the cable trays have to be? How many data cables have to be integrated? Are there requirements for curve radii? Can different cable systems be laid on one cable tray? Questions about questions that have to be clarified at an early stage and with everyone's participation.
6. As a result, the following parameters should be set:
   a. Voltage level
   b. Outer diameter of cable
   c. Bending radius
   d. Cable type designation
   e. Type (flexible or rigid)
   f. Special cables (e.g. fiber optics)
   g. Start and destination
   h. Labeling
   i. Own/external procurement or provided
   j. Type of fastening
   k. Necessary voltage level separation (according to VDE)
7. The longer the cable routes and the more expensive the cable prices, the more important it is to have a holistic, resource-saving cable route planning.
8. The calculation of the cable lengths is the basis for determining the cable quantities at an early stage. This can be done with cad support in databases (cable routing) or (for smaller projects) also with spreadsheet programs such as Excel. The results are then the familiar cable tension lists. From these, the corresponding occupancy lists must then be created for each individual cable rack. Optimally also database-based! Why? Each cable has its specific weight on a certain length and forms the basis for the design of the supports and the route size.
9. Once the platform size has been selected (usually with a 25 percent reserve), the brackets must be dimensioned. From experience, the editors of SicherheitsForum can report that, especially in the area of data centers, flatbeds already "sag" during acceptance without the occupancy of the user's own cabling. Why? Therefore, part of every planning should be the calculation of a maximum permissible cable load according to DIN VDE 0639 T1, taking into account the cables already specified and the manufacturer-specific cable weights (are given on every manufacturer's data sheet). On this basis, every user has the possibility to calculate his additional installations up to the maximum load as well. And the installer has the basis for selecting the necessary support system and its load. Siemens air hooks are the worst solution here!
10. Side effect of the calculations: An even load distribution can be aimed at!
11. It must also be weighed up whether one-sided route supports (especially for ceilings) are sufficient or whether a support on both sides is necessary. Especially when trailing cables, this means that the cable must be threaded through each bracket.
12. Today, cable hoists are realized by one company, especially for larger projects, irrespective of the use (heavy or light current cable). Therefore, it should also be considered to have the conception, planning up to the supervision of the implementation accompanied by specialized planning offices.
13. This also guarantees that the final documentation of the installer also reflects the final installed condition.

This technical report originally appeared in the printed edition SicherheitsForum 5-2021.

You want to read the articles of this issue? Then close right now here a subscription.