With Power over Ethernet (PoE), terminal equipment can be supplied with power directly via the Ethernet cable – now even powerful terminal equipment with up to 90 W, such as smart displays, intelligent PoE lights and actuators. This is why such systems are being used more and more frequently in building installations. With the introduction of remote power categories, PoE support is now also regulated for generic building cabling. However, in practice, the table-based interpretation of the installation standards turns out to be a complex task for planners. Matthias Gerber from R&M explains the problem – and the solution.
Following an increase in the number of PoE devices on the market, more and more building operators and planners are focusing on the topic, and initial experiences with large-scale PoE installations are now also available. But the standards seem complicated and the feedback from the market is not always positive. Is the connection with PoE cables really so complicated or what is the problem?
Gerber: “The problem is more in the way they are installed, not in the cables themselves. However, the two aspects are closely related. The EN 50174-2 standard for Europe and the ISO/IEC 14763-2 standard worldwide have been published since 2015 and describe the planning and installation of universal cabling systems. EN-50173 and ISO/IEC 11801, on the other hand, describe the specification of the individual cabling links. The installation standards build on the cabling standards and describe how cabling has to be installed in buildings.
“PoE end devices are now being used more and more frequently, and the growth in sensors and drives is exponential. This is why more and more building operators and planners are addressing the issue and are realizing that it is highly complex. In addition, the performance of PoE applications is constantly increasing: Today we have reached 4PPoE with 90 W. To take this increasing performance into account, the remote power categories RP 1 to 3 (Remote Power Category) were introduced to the standards two years ago. But that made the topic even more complex.”
Are these standards mandatory?
Gerber: “A standard is not mandatory per se; it reflects the state of the art. But most tenders for the installation of universal building cabling are based on these standards. In other words, the planner has to take this into account.”
And what do these RP categories mean, why did they make the issue so complex?
Gerber: “Initially, the power transfer of PoE was 13 W. Since 2018, 4PPoE has been able to transfer up to 90 W. However, where more current is flowing, the resistance generates more heat. That is why the remote power categories (RP1 – RP3) were introduced in 2020 to ensure the long-term reliable operation of the building installation even at higher currents. For RP1, up to an average of 212 mA are permitted and no special planning measures are required. But during operation, it must be ensured that the average current does not exceed the permitted limit.
“With 4PPoE devices, however, the supply current in a cable can be up to 500 mA. If a 4PPoE device is connected, in other cables of this installation bundle no PoE devices can be connected in order to compensate for the increased current. The standard therefore stipulates that appropriate warning signs must be attached to RP1 and RP2 installations. Before another PoE device is connected, compliance with the maximum permissible current must always be checked. RP1 and RP2 are easy when it comes to planning an installation, but it is very time-consuming for the building administrator in operation.”
Is that different with remote power category 3?
Gerber: “With RP3, the cabling is already configured during the planning phase so that all cables can transfer the maximum PoE current at the same time. This makes planning time-consuming, but during operation it makes the plant very reliable, as no further measures are required. For the operator, this is thus the preferred state of cabling – and the EN standard therefore recommends compliance with the RP3 category. It is even prescribed by the ISO/IEC standard.
“However, the challenge for the planner now is that with RP3 cabling, care has to be taken to ensure that the attenuation budget for data transmission is always adhered to even at increased temperatures and that the maximum permissible temperature in the cable is not exceeded.
"This is achieved by adjusting the link lengths depending on the ambient conditions of the installation. The installation standards offer tables for this purpose that show the temperature increase.”
But the planning and correct design of an RP3 installation does not seem to be that easy with these tables?
Gerber: “That’s the problem. In order to reduce the complexity of the tables and keep the number of tables manageable, considerable simplifications have been introduced. The consequence of this is that it has become very difficult to find the right parameters. What’s more, the conditions along a cable are not always the same. The standards require the temperature increases in the various sections to be determined individually and then averaged using a complex weighting procedure. The maximum permissible cabling length can then be taken from another table using this average temperature.”
That does sound very complicated, mistakes must be almost inevitable. Couldn’t it be made easier?
Gerber: “Yes – R&M developed a PoE Calculator back in 2015 and has now expanded it to include functionalities for the new RP categories. The
PoE Calculator offers building operators and planners several benefits: First of all, the planner can enter many more different parameters than are specified in the tables, which is much closer to reality. For example, you can enter the cable type that is actually used instead of having to assign the cable to a general category in the table.
“Furthermore, cable types, bundle thicknesses, environmental temperatures and other parameters can be entered for up to three segments of a cabling link. The PoE Calculator then immediately delivers the expected temperatures within the cable bundle of a segment and, as an essential criterion, the resulting maximum link length.”
How much time do planners save with the PoE Calculator?
Gerber: “The first time the data is entered, planners will not be much faster than with the tables. But they can change the various parameters very quickly. For example, they can choose a cable from a different category, make the cable bundle narrower, optimize the cable duct or ventilation, and thus change the underlying conditions. The simulation program immediately shows the result of these changes. That would be much too time-consuming with the tables. Nobody does that.”
R&M cites the documentation option as another major benefit. What does that mean?
Gerber: “With the documentation generated at the end of the calculation, the planner has automatically generated a description of their approach.
It defines all the underlying conditions and clearly documents compliance with the standard. These are the two major benefits of the PoE Calculator: The possibility for the planner to run through the parameters and get an immediate result, and, at the end of the calculation, the documentation for the building operator that the installation actually meets the specifications.”
Do other manufacturers also offer this?
Gerber: “There are one or two other spreadsheet calculators on the market – but, without wanting to brag, the R&M PoE Calculator is the best in terms of its functionality. But above all, it is the only one that generates this documentation according to the remote power categories.
“This is an enormously helpful and important document for planners, installers and building operators when it comes to verifying and proving that the installation complies with standards and is in line with the tender. R&M uses this document to list the RP categories in the warranty certificate and present them to the end customer as part of the R&M Freenet system and is the first manufacturer ever to do so.”