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56 Wire & Cable ASIA – JulyAugust 2015
Further consideration should be given to the correlation of
simulated data and that of the installation environment. On
one hand, the simulation may be based on a worst case
scenario. However, in reality, the duty cycle may dictate
that the power is only supplied for a fraction of the time.
Good installation practices should be implemented
wherever possible, such as minimising bundle sizes,
accounting for temperature rise for maximum cable
lengths, and keeping pathways and spaces free of
thermally insulating materials.
It is important to note that, while excellent correlation was
seen between simulated and measured results for a single
cable setup, this work was not intended to replicate the
behaviour of cables in bundles.
However, it is anticipated that good correlation
between theory and practice will also apply to bundled
configurations in free air and in a variety of cable
containment systems, ie tray, trunking, conduit, etc.
A comparison between the CCA 24 AWG UTP and Cat6A
26 AWG U/FTP samples show that it is possible for cables
with smaller conductors to radiate less heat than those of
larger conductors when supplied with identical DC current
values.
It is also known that the conductive foil in screened cables
act as a heat sink which helps to reduce the amount of
heat radiated from the cable[10].
Therefore, it is important to take into account the
construction of cable, and not only the conductor diameter
for PoE system deployment.
The increasing demand for more power supplied from
the Power PSE to the PD is obvious, with powering over
all four pairs expected to be IEEE standardised[11] and a
variety of non-standard products currently available on
the market which provide power levels in excess of those
stated in IEEE 802.3at.
Higher power levels will increase performance risk, but will
also allow PoE to be used for a wider range of applications.
Conclusions
A two-dimensional model was set up using COMSOL
Multiphysics software in order to replicate measured
results.
A test method proposed by IEC subcommittee 46C to
assess cables for Power over Ethernet was followed, which
outlined the measurement for heating data cables by DC
current.
Excellent correlation between simulated and measured
results for a single cable has been demonstrated. This
correlation encourages use of the software for the thermal
prediction of cables in densely populated networks.
It is also expected to provide a strong indication of
the temperature rise for varying bundle sizes, ambient
temperatures, and containment systems, etc.
The thermal performance of a CCA cable subjected to
DC powering has also been proven to radiate more
heat than cables which use solid copper conductors
using equal DC current values. Installations using PoE
technology differ greatly in terms of their configuration and
environment.
With an increasing demand for more power, which is likely
to require powering over all four pairs, further work is
required to investigate cable and component performance
in areas such as bundled cables, thermal behaviour in
different ambient temperature environments, cable reach
under PoE, and connector demating under load.
References
[1] IEEE Standard 802.3at, 2009
[2] M Gilmore, ‘The impact of copper clad aluminium (and steel)
conductors within balanced pair cables (intended for use within
implementations of generic cabling),’ FIA-IAN-002, 2011
[3] IEC Subcommittee 46C, ’Proposal for measuring of heating of data
cables by current,’ 46C/906/NP, 2009
[4] COMSOL Multiphysics:
[5] G J Anders, Rating of Electric Power Cables in Unfavorable Thermal
Environment, Wiley-Blackwell, pp 2-4 (2004)
[6] National Instruments LabVIEW:
[7] Minitab:
[8] J Wilson and C Hernández-Hall, Physics Laboratory Experiments,
Brooks/Cole, p 361 (2009)
[9] F S Akinnuoye, H Sasse, V Kang, A Duffy, ‘Heating Effects on channel
performance for Power over Ethernet (PoE) applications,’ Proceedings
of the International Wire & Cable Symposium (IWCS), November, 2013
[10] H Congdon, B Davis, ‘Mythbusting takes on shielded cabling,’ Bicsi
Presentation, 2009
[11] Four-pair PoE study group:
Paper courtesy of the 63rd IWCS Technical Symposium,
Providence, Rhode Island, USA, November 2014.
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