Select a rack system, Seccion needed (example), Protection, Installation, Selecting support

Select a rack system:
You need to know the following factors in order to select a rack system:

>The weight and diameter of the cables intended for use in the installation, and in future extensions.
>Any non-distributed loads planned (lamp fittings, electrical boxes etc.)
>The distance that can be allowed between supports or bearing points.
>The corrosion protection needed.
>The nature of the installation (open, closed etc.)
>The method of installation (wall, ceiling etc.)
>The need for earthing.
>Electromagnetic compatibility.
>Rack size: When the cables involved are known, check their weight-per-metre and cross-section in the manufacturer’s catalogue. Add 30-50% to each of these values to allow for future extensions.

>>Total cross-seccion needed: is found by adding up all the cross-section values of the cables planned and any future cables, plus the filling coefficient. The calculation involved is:

S=

K (100+a) 100

n

S= total section needed in mm2. K= fill coefficient: 1.2 small cables / 1.4 power cables. a= space reserved for future extensions (30-50%). n= sum of the sections of the cables to be installed in the cable tray.

When the value of “S” is known, the total weight per metre of the cables “P” is found from the catalogue, increasing the value by that same percentage. This value “P”, in kilos/metres, is converted into Newtons, since that is the unit used in the rack load-capacity graphs. Conversion: 1 kilo = 9.8 Newtons. With reference to these S and P values, find the most suitable S and P values in the rack catalogue, erring on the side of excess. If an exceptional load is planned at some point in the installation, select a tray with higher performance values for there. back

>>Example:

 

 

 

 

 

 

 

 

 

 

 

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>>Protection against corrosion: Most rack systems available are made of steel.
This material oxidises easily, causing significant economic losses. In the case of trays, there may also be quality-of-service problems. To remedy this, various surface-treatment processes based on zinc are used.

The commonest and most successful in industry are, in order of efficacy:

>G.S: Sendzimir galvanizing.
>E.Z: Electrogalvanizing.
>Z.B: Electrogalvanized bichromate (Yellow).
>G.C: Hot-dipgalvanized.
>INOX: Stainless steel.

There are other types of plastic coverings based on various products: PVC, Polyethylene, Polypropylene, Epoxy resin etc.
These are more attractive in appearance, but give results that are very inferior to zinc-based coatings. They are fragile, and the range of working temperatures is much narrower than zinc. back

>>Method of installation: On the wall, ceiling or the floor. See Rejiband. back

>>Selecting the type of support: Once the rack has been chosen, suitable supports in terms of the type and method of installation must be chosen. They must have sufficient load-bearing capacity to withstand safely the system of trays plus the accessories selected, and must have the same degree of protection against corrosion.

PEMSA gives the load-bearing capacity (N) of all its supports in accordance with standard IEC 61537, and the capacity of their protective finish. When the Safe Working Load (SWL) for the rack chosen is known in Newtons per metre, the support must be able to withstand the value of this SWL x L, where:

>L = the distance between the supports in metres. back