WCA July 2015

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Wire & Cable ASIA – July/August 2015
Individual Value Plot of Differences
(with Ho and 95% t-confidence for the mean)
Differences
Δ Conductor temperature (ºC)Current (A)
Cat6A-26AWG
CCA-24AWG
Cat5e-24AWG
Current (A)
Δ Conductor temperature (ºC)
Measurement
Simulation
Approximation
❍
❍ Figure 4: Simulated, measured and approximated change in
conductor temperature
❍
❍ Figure 5: Individual value plot of temperature differences
❍
❍ Figure 6: Measured change in conductor temperature
Using the approximation, a current of 3A would provide
a temperature rise of 20.7°C for a single cable within an
environment fixed at 20°C.
The correlation between simulated and measured results
was further investigated from a statistical point-of-view
using a Paired t-test via Minitab software[7] .
Figure 5 shows an individual value plot of the temperature
differences between simulation and measurement, which
also shows the 95 per cent confidence interval based on
these differences.
The results shows that 95 per cent of additional simulated
and measured values are expected to fall within the ±0.1
difference range, confirming excellent correlation. As
such, the null hypothesis of no difference in mean values
between the two sets of data is not rejected.
Copper clad aluminium
A sample of UTP CCA cable with 24 AWG conductor size
was acquired and measured as per the Cat6A 26 AWG U/
FTP cable sample in section 3. The DC loop resistance of
the pairs under investigation for each cable type are given
in Table 1. For comparison, a Cat5e UTP cable with 24
AWG solid copper conductors was included in the study.
Due to the high resistance of the CCA cable under
investigation, the high voltage required to provide a current
of 2.2A was not possible using the bench power supply.
In other words, as the temperature and resistance
increased, the voltage required (in order to meet Ohm’s
Law) was larger than the maximum voltage 60V) of the
bench power supply. A current value of 1.95A was chosen
in order to generate the fifth data point.
Figure 6 shows the change in conductor temperature,
versus DC current level, which was calculated from the
measurement. For the CCA cable sample, approximated
conductor temperature rise was found to be:
(INSERT IMAGE/CALCULATION 2 HERE)
Temperature rise due to the Joule heating effect is known
to be proportional to I2R losses[8] so, as current is fixed for
each measurement point, the resistance of the cable pair
under investigation will differentiate temperature rise from
one cable to another.
Therefore, as expected, the cable with highest DC
resistance will have the most temperature rise, and vice
versa.
Discussion
Heating cables is known to increase attenuation[9] which
has a limiting effect on cable reach. In relation to PoE,
the maximum temperature is likely to be in the proximity
of the energised conductors which may be used for data
transmission.
Therefore, the consequences of DC powering on
attenuation of the same pair should be taken into
consideration.
The results presented in this paper show the temperature
rise of one pair energised with DC power using a cable
located in a controlled 20°C environment. Realistically,
the ambient temperature will vary from site-to-site, and
therefore, caution should be taken when installing PoE
systems into uncontrolled and/or warmer environments.
AWG DC loop
resistance (Ω)
Cat6A 26 23.3
CCA 24 28.4
Cat5e 24 18.2
❍
❍ Table 1: DC loop resistance of pair under investigation for each
cable type