The case for Cat 6A over Cat 5e in PoE applications
A technical paper from General Cable examines DC resistance and power dissipation, and translates the data into potential energy-cost savings.
A paper authored by General Cable data-communications products engineer Rob Gould makes the case for the use of Category 6A cabling rather than Category 5e cabling for applications in which Power over Ethernet (PoE) will be employed.
Focusing primarily on the original 802.3af PoE specifications, but also considering the more-recently defined 802.3at PoE Plus specs, the paper provides documentation of testing under which Cat 5e performance was compared to Cat 6A performance supporting a VoIP phone drawing 4.93 watts and a wireless access point drawing 7.5 watts of DC power. The performance characteristic under test was DC resistance, and the practical result of a cable's DC resistance in these setups is power dissipation.
For both devices, 328-foot cable runs of both Category 5e and Category 6A were deployed. In the case of the VoIP phone, on the Category 5e circuit approximately 82 milliwatts of power were dissipated, while on the Category 6A circuit approximately 56 milliwatts were dissipated. In the case of the wireless access point, approximately 201 milliwatts of power were dissipated on the Category 5e circuit and approximately 137 milliwatts on the Category 6A circuit.
The paper then calculates long-term savings, in electricity costs, that will be gained by the use of Category 6A rather than Category 5e cabling. It later expands the findings to PoE Plus scenarios.
In the paper's conclusion, Gould states, "With the world's ever-growing demand for energy, finding new and more-efficient ways to deliver it is essential. PoE not only decreases infrastructure material, when run over Cat 6A, it delivers power more efficiently. For customers seeking high efficiency and future growth potential with their networks, once choice for PoE stands above the rest - Cat 6A cable."