Compliance to Power-over-Ethernet safety standards is critical when moving beyond 60W

   Power over Ethernet (PoE) offers convenience, flexibility, and enhanced management capabilities by enabling power to be delivered over the same CAT5 cabling as data.  The current generation of standards-based technology enables up to 60 watts of power to be delivered over four pairs of cabling, which also improves efficiency when compared to earlier two-pair solutions. 

   As the industry moves toward delivering even more power over the CAT5-or-better cabling infrastructure, system designers and network administrators alike, need to understand various emerging technology options, including those developed under the auspices of the IEEE, and others that bring expensive and cumbersome deployment complications and, potentially, safety risks. 

   For instance, some manufacturers have touted 100W-per-port solutions that do not perform detection before power-on, which can be very dangerous.  Others offer 200W/port solutions that are even more dangerous unless they use a hard re-settable fuse at every Power Sourcing Equipment (PSE) unit, or if a certified electrician deploys the cables.  The only safe approach for powering devices over Ethernet cabling is to follow IEEE802.3at-2009 specifications. 

   This is what the HDBaseT Alliance is doing as it develops 100W power specifications for products that transport uncompressed, high-bandwidth multimedia content, 100BaseT Ethernet, power, and various control signals through a single LAN cable. As a cross-industry organization formed to promote and standardize whole-home HD multimedia content distribution, the HDBaseT Alliance has created a 5Play™ feature set that converges uncompressed full HD digital video, audio, 100BaseT Ethernet, IEEE802.3at-compliant power and various control signals so they can be transported over a CAT5 cable. 

   The key differences between the HDBaseT-powering approach and those from other independent manufacturers pursuing higher power levels are that it:

•Complies with the section 33.7.1 of the IEEE802.3at-2009 standard, which mandates that all PSEs conform to International Electrotechnical Commission (IEC) 60950-1:2001 specifications including classification as a Limited Power Source (LPS) carrying no more than 100 volt-ampere (VA) – or 100W – per port without the need for special over-current protection devices, and

•Performs Powered Device (PD) detection followed by PD classification to determine a PD’s consumed power level prior to its ignition.

   There are other standards to consider as the industry moves to higher powering.  For instance, HDBaseT-powered TV and audio equipment will be expected to comply with UL 60065, which requires that a fire enclosure be used for loads above 15W.  Consequently, even if the TV load meets the sub-100W/port LPS requirement of IEC 60950-1:2011, it will still need a fire enclosure.

   Moving beyond the LPS requirement to greater-than-100W/port implementations requires that the cables be protected with special flame-resistant conduit that is attached to the PSD and PD inputs through metal boxes that are enclosed in brackets.  This requirement applies for cable lengths greater than 10 feet (3.05m). 

   Below 10-foot cable lengths, it is possible to use the same four-pair PoE/HDBaseT cabling system (i.e., data cable plus RJ45 connector); however, the cable will have specific feature requirements beyond those of typical CAT5/E cable.   Figure 1 shows a circuit meeting these requirements.

Figure 1:  Example of a circuit featuring two separate ports, each carrying 100W.  Power is calculated at the PD side, and LPS requirements apply to each port.  NOTE:  According to the National Electric Code (NEC), multiport midspans that power PDs using this approach must carry a nameplate with the power rating for each port. (Click here for enlarged image.)

   Some manufacturers try to circumvent the 100W ceiling and associated protection requirements by suggesting that the ceiling can apply to each of two PSEs running on two separate circuits within the same cable.  Using this logic, they believe that a compliant PSE can support either 1 x 95W, alone, or roughly double that when two PSEs are paired on the same cable. 

   This is incorrect—and dangerous—thinking.  As specified in the IEEE802.3at-2009 standard, the 100W LPS power ceiling is measured at the physical connector.  Restrictions for power sources with and without overcurrent devices are clearly defined in Tables 2B and 2C of the Underwriters Laboratories, Inc. (UL) CAN/CSA-C22.2 NO. 60950-1-07 + UL 60950-1 document (see Tables below).  The fact that there may be two PSEs on the circuit is irrelevant from a UL point of view, since is an “inside the box” power arrangement that ends at a single connector, which is the only output power connector and must not exceed 100W.

(Click here for enlarged image.)

(Click here for enlarged image.)

   The only way to implement powering at 250W (or 250VA) is to use a circuit breaker or fuse at each port, or have a certified electrician install the cabling, which effectively negates the deployment benefits of PoE technology.  Figures 2a and 2b show the proper configurations for delivering greater than 100W over all wires (e.g., 200W) in two different single-port scenarios. 

   In both cases, a metal enclosure is required if the total PD load is greater than 100W for information data equipment, or greater than 15W for TV and audio equipment. In Figure 2a, a non-standard cabling infrastructure must be used to ensure safety, RJ45 connectors cannot be used directly at PSE and PD inputs, and a certified electrician will likely be required for installation.  In Figure 2b, a typical PoE/HDBaseT cabling system can be used, but special cabling must also be specified.  In summary, the use of a standard Ethernet-cabling infrastructure for a single port delivering greater than 100W is simply not safe under the NEC standard.