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There has been a great deal of argument in recent times about the benefit or otherwise of using wire mesh cable trays to carry Category 6 cables. It should be noted, however, that this is a controversy which only seems to dog the UK market; in the US and in Europe the need for wire mesh trays to prove themselves has long since passed. But we British, it seems, are never content to accept anything we have not seen proven for ourselves and so in many instances cable installers are ignoring the advantages and benefits of wire mesh trays in favour of sticking with practices which actually offer less protection to cables in certain crucial areas.

To encapsulate what any installer needs to know; wire mesh cable trays offer protection to cables from environmental dangers and they do not affect the performance of either Cat 5 or Cat 6 cables. I'll say that bit again: in independent tests it has been proven that wire mesh cable trays do not affect the performance of either Category 5E or Category 6 cables.

So why install cable trays at all? Aren't the cables perfectly safe in floor voids? Perhaps, but can you be certain the end-user will never experience leaky plumbing, problems with sprinkler systems, spillages or other forms of water penetration to the floor space? The fact is that in any environment there is always the chance that water – or other liquid products in an industrial environment – will get through the floor or the walls and sit in the floor space. It is also a fact that if and when this happens, cables which are placed directly on the floor or on cable matting will be sitting in this water. One way to protect them is sealed trunking. Another is wire mesh cable tray. The wire mesh will raise the cable off a potentially damp surface and, because it is an open system, will allow any water which drips onto the cables to either fall through or evaporate off.

Wire cable trays can also protect the cable during building work. Cable tray is not going to protect the cables from malicious damage, but, by raising them off the floor and by making them more obvious to follow-on trades it gives them a better chance of surviving than simply leaving them lying about on the floor. Also, once the cables are installed, direct onto the floor or onto cable matting it can be more difficult to identify each run and the cooling effect of airflow around the cables is restricted. When additional cables are added, the lack of any clearly-defined pathway – such as cable tray – will mean that new cables will simply take the shortest, easiest path, ignoring installation standards and practice.

Data cable manufacturers consistently recommend that their cables are installed in some appropriate containment raised above floor level. But what is the good of putting them in wire mesh trays to help them when they are first installed, if months or years later the cables are going to start to fail because of the forces exerted on them by the trays themselves? Results of recent independent tests have shown that wire mesh trays do no harm whatever to the cables they carry.

Intertek Testing Services carried out this research. This is a division of ETL, a testing, inspection and certification service. The objective of the test programme was to examine the short and long term effects on Category 6 cables, when subjected to pressure from the total weight of cables installed in a wire tray containment system. During the test, 90 m lengths of Category 6 test cable were placed in a wire cable tray, subject to zero load and tested to the requirements of TIA/EIA-568-B-2-1 Draft 5.

The cable was then subjected to a physical load equivalent to placing it at the bottom of cable laid to a depth of 200 mm. This was achieved by placing Lexan strips on the cable, with a weight corresponding to a total of 40 category 6 cables. A second set of measurements was taken, providing a comparison of the performance of the cable in the wire tray before and after loading. The test was repeated a third and fourth time with the cable loaded and unloaded on a flat even surface. The key finding of these independent tests, carried out under the control of ETL was that the physical load on the cables at the pressure points of the cross wire had no negative impact on cable performance.

Also, in temperature cycling tests, designed to age the cables to ensure that negative effects did not occur over time, it was found that a containment system which allows air to circulate freely, provides a positive advantage compared to a closed system or flat base because the open system prevents unacceptable temperature rises.

So, with all this to support the use of wire trays, why are some people still inclined to think that they are not up to the job. Tim Oldershaw is chairman of BSI TCT7/-/2 and the UK's principle expert to the European committee on cabling installation standards, and was involved in drafting the current standard EN 50174-2. He is convinced that the confusion about wire trays stems in part from the section of the standard concerned with electromagnetic interference properties. He says: "Self evidently, basket has limited protection against electromagnetic interference when compared with steel trunking because it does not provide total enclosure. But so what? It is not designed to provide this sort of protection, though, obviously it provides more protection than laying the cables directly onto the floor or using cable matting, which provide no protection at all. The standard makes it clear that while separation is the best form of protection, where this cannot be achieved, an electrically and physically continuous steel trunking may possibly be the only form of containment relied on as the sole form of protection. The standard provides this information in the form of a diagram in which, against basket, the word poor appears.

"Where high level electromagnetic interference protection is not required – as in the vast majority of applications - there is absolutely no reason not to use basket. Unfortunately, it seems that some people looking at the standard can misinterpret a diagram in the section on electromagnetic interference protection. "

Mike Gilmore, chairman of both BSI TCT7/-1 and the European committee on cabling design standards, attempts to clarify the situation. He says: "EN 50174-2 concentrates overmuch on electromagnetic behaviour. However, it is only one of the parameters that are now being used to define the cabling environment. We use the acronym MICE to define the installed environment (Mechanical, Ingress protection, Climatic, Electromagnetic) and for the M, I and C aspects then basket can offer significant advantages. As the EN 50174 series of installation standards are currently subject to revision I would hope that appropriate changes are made to clearly allow any cable management system provided that the cable supplier supports its use for the particular cable type to be installed."

Putting cables direct onto the floor or even onto cable matting because you do not trust wire mesh cable tray is a practice based on a false premise that actually places cables in greater and more immediate danger than using basket ever will.