R&M - Power over Ethernet. The idea is impressively simple: The supply current for the Ethernet device flows directly through the data cable. However,there are limits that complicate things. One of these is the link length. As the current causes the cable to warm up, the attenuation increases which reduces the possible transmission range. This is particularly true of the new 4PPoE (4-Pair Power over Ethernet) with a power of 55 or 100 watts, where up to one ampere can flow through each twisted pair.
Cat. 5e installation cables with a conductor cross section of AWG 24 (0.22 mm2) quickly reach their "natural limits." They grow hot quickly, especially when the heat is not being efficiently removed from large cable bundles. Cat. 6 or Cat 7A cables with cross sections of AWG 23 (0.26 mm2) or AWG 22 (0.33 mm2) come with the benefit of reduced resistance.
For each project it is important to consider the applications for which the cabling solution is configured. Is 1 Gigabit Ethernet with class D or E cabling sufficient in the long term? Or is 10 Gigabit Ethernet with class EA cabling or higher required? Planners will also have to consider the PoE parameters more carefully in the future. What are the specific limits? What is the load carrying capacity of a planned installation? What must be considered when planning a new future-proof installation?
R&M has developed a PoE calculator for this, which determines the possible link lengths by simulating different applications. What is particularly noteworthy is that cable types, bundle strengths, ambient air temperatures, and other parameters can be specified for up to three segments of a cabling link. The spread sheet program calculates the expected temperatures within the cable bundle of a segment and, crucially, the resulting maximum possible link length. The program takes into account the latest international standards.
The large number of configurable parameters in the tool allows users to calculate the permissible transmission lengths for individually specified applications. Playing with entries will quickly reveal the limits through negative link reserve values: The planned transmission range is then not achieved, at least not with a reliable data transmission.
