Special report: Remote powering – Things are hotting up

Much of the work undertaken to date by cabling standards bodies on behalf of IEEE involved cable bundles in ‘free space’ which hardly mimics real installation conditions. In contrast, the CLC work will specifically investigate the installed environment in detail and include the installation of cable bundles in various pathway systems such as conduit, trunking and within insulation materials and fire barriers. In addition, the impact of densely packed bundles of cables will be similarly investigated.

Work has already begun in North America and in Sweden to construct a database of test results but the earliest work was used to define a test rig and test methodology in order to allow comparison of the data obtained.  This test protocol is now available at www.fia-online.co.uk/eservice-standardsfiaintro.htm and any organisation wishing to participate in this work is welcome to download this document to establish the requirements for the test procedure. The document also identifies the format in which we wish to receive the data generated by each of the tests.

The testing procedure is not restricted to the determination of the thermal behaviour of bundles of cable when subjected to specific installation conditions. It can also be used to obtain standard based results during the development of cable management system designs. For example, a trunking supplier may want to profile the comparative heating effect of different extrusion profiles. Similarly, a fire barrier product supplier might wish to assess the impact of different fire stopping materials or while varying dimensions of the resulting fire barrier.

Of course, establishing the test rig and obtaining the correct power supplies etc. is a time-consuming and costly exercise and would only be justified if an extended period of testing was to be considered. However, in the UK we are fortunate that De Montfort University, Leicester, has a test rig with suitable power supplies and temperature measurement systems and is willing to enter into service contracts with organisations wishing to participate in this work on shorter or simpler test programmes. Dr. Alistair Duffy is in charge of the facility and the work and he can be contacted at apd@dmu.ac.uk.

So for any organisations are interested in either using the Loughborough University rig or undertaking their own independent work, a European support group has been established that is able to answer any questions and provide guidance in advance of any work beginning. The benefit of the support group is that they will be aware of all the work that has been completed, underway and also that which is already planned. This will prevent duplication and speed up the entire process of data collation. The support group is being coordinated by Mike Gilmore, director of standards@fia (contactable at  standards@fia-online.co.uk).    

Early work has already re-confirmed the temperature rises in small bundles as predicted/measured in the work for IEEE during their consideration of solutions for PoEplus.  However, the most interesting results will come for delivery of currents greater than those both currently implemented by IEEE – and those planned by IEEE for the immediate future.  We have seen rises of 20 degree Celsius when the current rises to levels proffered by some of the most powerful, non-standards based, mid-span power insertion devices. It is expected that similar rises will be observed when lower levels of current are applied to bundles in insulated spaces and in spaces with limited or no ventilation.

Once an adequate data set has been collated, the Technical Report itself will be completed. 

Overall the Technical Report focuses on planning, installation and operational guidance for cabling designers, installers and users. The immediately planning impacts are clear and may require reductions in channel lengths to offset the  most severe thermal impacts. This is not a minor issue since if a user wishes, from the outset, to provide widespread distribution of remote powering cabling to serve the latest MagLoks, lighting systems, surveillance cameras and door entry systems, the simultaneous delivery for high speed data services over the same cable bundles may be restricted in terms of overall length – well below the 90 metres link lengths that are typically considered to be the norm.  Such restrictions could have substantial cost impacts in terms of the location of comms rooms and can therefore not be ignored and operational planning, well in advance, is a great deal better than finding out about problems once the systems have gone “live”

The TR will concerns itself with more than cable temperature rises since higher currents create concerns for connector damage which may have an impact on both cabling and equipment connections but main focus will be the operational impact on cable bundles and installation practices.

The main purpose of this article is to advertise the current phases of testing using the standards-based approach. If you wish to obtain more information please feel free to contact Mike Gilmore (as detailed above) who will either provide additional detail or, as necessary, put the reader in touch with the European support group. If you wish to undertake testing but feel that some hand-holding is required then please contact Alistair Duffy who can advise on the commercial arrangements for using the De Montfort University, Leicester, test rig. At this stage the more data we can collect, the happier we will be since it provides greater insight into the wider picture and allows the Technical Report to be developed as quickly as possible. 

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