Network Infrastructure Blog

The 2017 edition of the NFPA 70® National Electrical Code® (NEC) contains a new Article 840, Part VI requirement addressing premise powering of communications equipment over communications cable. This requirement only applies when the power supplied is greater than 60W (i.e., it does not apply to IEEE 802.3 Type 1 (15W), Type 2 (30W), and Type 3 (60W) PoE implementations). In this case, the maximum current that may be carried by a cable conductor is determined by the conductor gage (AWG) size, number of 4-pair cables in a bundle, and the mechanical temperature rating of the cable as provided in Table 725.144 of the NEC and excerpted below. Note that this table is based on an ambient temperature of 30° C (86° F).

As an example, the maximum ampacity of one 24 AWG category 5e conductor, mechanically rated to 60° C and contained within a bundle of 62-91 cables, is 400 mA (800 mA per pair). Since the IEEE P802.3bt Type 4 90W application specifies a supported current of 948mA per pair, this example product and installation configuration would not be compliant to the NEC requirements for support of this application. To overcome this restriction, the NEC provides a provision to use a limited power or LP-rated cable jacket to support increased ampacity. Another alternative allowed by the NEC is to use cables having larger diameter conductors and/or a higher temperature rating to reach the desired ampacity capability.

Siemon recommends the use of its shielded category 6A and category 7_A cables (having 23 AWG and 22 AWG sized conductors, respectively) for support of 60W and higher power applications because these cables offer the same application support capability as LP-rated cables with the added benefits of greater heat dissipation, power efficiency, bandwidth, and noise immunity. Note that these cables are mechanically rated to 75° C (167° F) and, according to the NEC table (refer to the cells highlighted in yellow), are suitable for support of at least 500 mA per conductor/ 1 A per pair current levels in bundle configurations of up to 192 cables in 30° C (86° F) ambient temperature environments. Siemon has developed bundling recommendations for a much broader range of ambient temperatures. Following these bundling guidelines ensures that an -LP rated cable is not required to support greater than 60W applications within the environments for which Siemon cables are rated.

Wideband multimode fiber (WBMMF), officially designated as OM5, is a recently released fiber medium that is now recognized within both the Telecommunications Industry Association (TIA) and International Electrotechnical Commission (IEC) standards. OM5 fiber specifies a wider range of wavelengths between 840 and 953nm to support wave division multiplexing (WDM) technology and is fully backwards compatible with existing OM4 fiber specifications.

WDM technology provides the capability to either increase transmission speeds or reduce fiber strand counts by a factor of 4. For example, using standard OM3 or OM4 multimode fiber, 100 gigabit speeds require the use of 8-fibers via 100GBASE-SR4. In contrast, using 25GBASE-SR specifications, 100 gigabit OM5 fiber links could be created using 2-fiber 25 gigabit channels on 4 different wavelengths. Similarly, using 100GBASE-SR4 specifications, 400 gigabit OM5 fiber links could be created using 8-fiber 100 gigabit channels on 4 different wavelengths.

However, it is important to note that there are no applications currently under development within the Institute of Electrical and Electronics Engineers (IEEE) to operate over this medium. In addition, because IEEE typically develops applications based on a significant installed base, it is not certain when and if any application will be developed. Further, OM5 carries a significant cost premium over OM4 and a premium will also apply to any future transmission equipment.

The recent release of IEEE 802.3by-2016 (25GBASE-SR) and the pending IEEE P802.3cd (50GBASE-SR) – anticipated to release in 2018 – demonstrates IEEE’s commitment to the development of higher capacity applications over the installed base of OM3 and OM4 multimode fiber. There is also work on singlemode technologies for short reach (500m) applications via the pending IEEE P802.3cd (100GBASE-DR) and IEEE P802.3bs (200GBASE-DR4/400GBASE-DR4) that may provide a case for singlemode fiber to be considered.

As a result of this pricing premium and application uncertainty, at this time Siemon still recommends deployment of OM3 or OM4 8-fiber MPO/MTP connectivity for seamless migration from current standards-based 2-fiber (10GBASE-SR, 25GBASE-SR) and 8-fiber (40GBASE-SR4, 100GBASE-SR4) applications to future applications.

View our full line of OM3 and OM4 Advanced Fiber Solutions.

It is well understood that deploying 30 W and higher remote powering applications, such as Power over Ethernet (PoE) and Power over HDBaseT (POH), over balanced twisted-pair cabling produces a small degree of heat build-up within bundled horizontal cables. This heat build-up does not affect safety, but can affect transmission performance and long-term mechanical reliability. This can vary over differing cable categories and constructions as, for example, cables with larger conductors inherently have less heat build-up due to lower resistance and cables with metallic elements have less heat build-up due to superior heat dissipation properties. Different pathway styles (e.g., conduit versus free air) can also affect heat build-up within cable bundles.

Managing cable bundle size is important to ensure that heat build-up does not exceed the mechanical rating of the cables and that appropriate channel length de-rating is applied to offset additional insertion loss due to increased ambient temperature. While ISO/IEC TS 29125 and TIA TSB-184-A address recommendations for cabling supporting remote powering applications, these technical bulletins are generic in nature and not directly applicable to Siemon cables, which, depending on cable type, can support higher mechanical temperature ratings and offer superior heat dissipation.

The table below depicts recommended bundle sizes for Siemon horizontal cables supporting a variety of remote powering applications. Note that these bundling recommendations are applicable to cables installed in all pathway types, so they are more conservative than would be specified for cables in free air (i.e. non-conduit) installations. Consult the infrastructure design experts at Siemon for information on bundle size recommendations for cables installed in open pathways.

When in doubt about cable mechanical or heat dissipation capability, installation environment, or remote powering application, a conservative practice is to limit maximum bundle size to 24 cables. With the exception of the few instances noted below, this easy to remember practice addresses the majority of media, environmental, and application scenarios.

Q:         When will the 2.5G/5GBASE-T Ethernet Standard be ratified?  The IEEE 802.3bz™ “Standard for Ethernet Amendment: Media Access Control Parameters, Physical Layers and Management Parameters for 2.5 Gb/s and 5 Gb/s Operation” was approved by the IEEE-SA Standards Board on September 22, 2016.

Q:         Will the installed base of category 5e and 6 cabling support 2.5G/5GBASE‑T? 2.5G/5GBASE‑T operates over “defined use cases and deployment configurations” of category 5e/class D and category 6/class E cabling. Neither 2.5GBASE-T nor 5GBASE-T are intended to operate over the entire installed base of category 5e/class D and category 6/class E cabling.

Q:         How will I know if my installed category 5e or category 6 cabling plant will support 2.5G/5GBASE-T? TIA TSB-5021 and ISO/IEC TR 11801-9904 address the evaluation of installed category 5e/class D and category 6/class E cabling for possible support of 2.5GBASE-T and 5GBASE-T. Extended frequency characterization (i.e. performance above 100 MHz for category 5e/class D cabling), signal to alien crosstalk assessment, and additional field test qualification measurements will be described within these documents. It is important to keep in mind that these field assessment methods are still under development and will likely prove to be very time-consuming and onerous to implement and may not be fully conclusive.

Q:         Is 2.5G/5GBASE-T operation covered by Siemon’s category 5e and category 6 system warranties? Because support of 2.5G/5GBASE-T by category 5e/class D and category 6/class E cabling is dependent upon environmental (e.g. alien noise levels) and installation (e.g. channel length and cable bundling) conditions, Siemon can only guarantee support of the  2.5GBASE-T and 5GBASE-T applications with category 6A/class E_A and higher performing cabling systems.

 Q:        What grade of cabling should be installed to ensure guaranteed support of 2.5G/5GBASE-T? Siemon recommends that category 6A/class E_A and higher grades of cabling be specified to support all new IEEE Std 802.11ac™-2013 based enterprise wireless access point uplink connections, even if it is anticipated that 2.5GBASE-T or 5GBASE-T equipment will be deployed. A recommendation to install category 6A/class E_A or better cabling for all new installations intended to support 2.5G/5GBASE-T also appears in both TSB-5021 and ISO/IEC TR 11801-9904. Since category 6A/class E_A and higher performing cabling is also guaranteed to support 10GBASE‑T, this design approach maximizes the lifecycle of the cabling infrastructure.

Published in 2011, the Construction Products Regulation (CPR) defines the fire performance of all construction products. Under this regulation, all construction products and building materials installed in the European Union (EU) must contain the CE mark that provides proof of compliance.

How Does CPR and the CE Mark Relate to Communications Cable?

As of 10th June 2016, copper and fiber telecommunications cabling is now subject to the CPR with a one year transition period. This means that as of 1st July 2017, all copper and fiber cables supplied to EU member states must comply with the regulation and carry the CE marking. With CPR specifications developed and adopted by EU member states, the regulation facilitates trade between EU member states for any construction products that are intended to be permanently incorporated into a building.

It’s important to note that the CE mark does denote quality—it means that the product meets standards for health, safety and economy of energy. It also only relates to cables intended for permanent installation, which excludes non-fixed cabling infrastructure components such as patch cords and jumpers.

For more background on CPR, visit: Construction Products Regulation (CPR)

 What are Euroclasses?

Under the CPR, existing IEC 60332 flammability ratings will be replaced by different reaction to fire performance known as Euroclasses. There are seven Euroclasses—A, B1, B2, C, D, E, and F—whereby A is the most flame retardant and F is the least. The requirements for the Euroclasses are outlined in the recently published standard EN50575, Power, control and communication cables – Cables for general applications in construction works subject to reaction to fire requirements.

 Who Determines what Euroclass is Required?

EU member states are required to follow CPR and each EU member state will decide which Euroclasses to adopt for their specific construction standards and regulations. Euroclasses B through D are considered low fire hazard cables and must meet EN 50399 Flame Spread testing in addition to EN 60332-1-2 while Euroclass E need only meet EN 60332-1-2 and Euroclass F has no determined performance. Broad use of Euroclass D and E is expected for residential and standard commercial premises throughout the EU.

 How Does the Regulation Impact Cabling Manufacturers?

Any cable manufacturer wishing to sell fiber and copper communications cable into EU is required to test their cables for CPR compliance with a “notified body” required to certify test results. Manufacturers must then draw up a Declaration of Performance (DoP) and affix the CE mark to its cable products and product labels. The purpose of the DoP is to hold manufactures responsible for conforming to the declared specification. As previously noted, all manufacturers supplying copper and fiber cables to EU member states must issue a DoP and affix CE marking to cable by 1st July 2017.

 What is Siemon Doing to Prepare for CPR Compliance?

As a leader in the structured cabling industry, Siemon is currently working with Notified Bodies to test its existing copper and fiber cables and establish Euroclass specifications. We are on schedule to receive Euroclass D and E certification for the bulk of our copper and fiber cables and are targeting to offer CPR compliant product with CE marking by the end of this calendar year. Further communication regarding product availability will be forth coming, and Siemon will continue to monitor all standards, trends and adopted Euroclasses within the EU and adapt cables where necessary.