Optimal thermal behavior, longer links

Power over Ethernet – that is, supplying power to terminal equipment over data cables – is increasingly popular. In the future, all four twisted pairs are to be used for the power feed (4PPoE). Up to one ampere is supposed to flow over each twisted pair. On the one hand, this makes new applications possible. But on the other, it means that network cables heat up more. Warmer cables attenuate data transmission. This means network planners have to do their calculations with shorter link lengths.

090.2217In a typical U/UTP cable, the PoE-related heat-up rises by a factor of 5. A shielded cable ranges from a factor of 2.5 to 3 depending on the design. This means: In a bundle consisting of U/UTP cables, the temperature rises by twice as much as in a comparable bundle consisting of S/FTP cables. In shielded cables the metal in the shield helps to transport the heat from within the bundle to the outside.

R&M wanted to know how the WARP cable would behave when using PoE. The R&M Cat. 6A WARP cables are technically unshielded UTP cables. But their jacket contains a special foil to reduce data interference from adjacent cables (Alien NEXT). These short metal foil segments (wave reduction pattern, WARP) suppress Alien NEXT, but do not have to be grounded, which saves on installation costs.


The curve in the comparative test confirms the favorable thermal behavior. WARP cables heat up by 14 °C less in connection with the largest cable bundle and, in this case, allow the transmission distance to be 11% longer than with U/UTP cables. A factor of 3 can be assumed for the heating up of R&M WARP cables, as is the case with a shielded cable.

Installations featuring regular commercial U/UTP Cat. 6A cables and R&M WARP Cat. 6A cables can be simulated with the PoE calculator from R&M. This tool can be employed to calculate the anticipated temperatures in a cable bundle and from that, the maximum length of a cabling link. In the White Paper “4PPoE – Parameters for Network Planning” R&M provides information on the physical backgrounds.

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Matthias Gerber

By Matthias Gerber

Market Manager LAN