The key to POE over 60W is to meet safety standards

Power over Ethernet The standard provides convenience, flexibility and enhanced management capabilities to deliver power over the same Category 5 cable used to transmit data. The current generation of standards-based technology can deliver up to 60W of power over four pairs of cables, which is also more efficient than the previous generation's two-pair solution.

As the industry moves to deliver higher power over Category 5 cabling (or better cabling architectures), system designers and network managers must understand the various emerging technology options, including standards developed under the auspices of the IEEE, and other standards that bring high costs and cumbersome deployment complexity, as well as potential safety risks. For example, some manufacturers have promoted 100W per port solutions, which do not perform any testing before power is applied, which is a dangerous omission. Other solutions that provide 200W/port are even more dangerous unless hard-resettable fuses are used at each PSE (power supply equipment) unit, or the wiring is done by a qualified electrician. The only safe solution for powering devices on Ethernet cables is to comply with the IEEE802.3at-2009 specification.

The HDBaseT Alliance is developing a 100W power specification for products that transmit uncompressed, high-bandwidth multimedia content, 100BaseT Ethernet, power, and various control signals over a single LAN cable. The HDBaseT Alliance is a cross-industry organization dedicated to the promotion and standardization of high-definition multimedia content throughout the home. It has created a "five-play" function that aggregates uncompressed, full HD digital video, audio, 100BaseT Ethernet, IEEE802.3at specification power, and various control signals for transmission onto a Category 5 cable.

Although independent manufacturers are pursuing solutions for higher power levels, HDBaseT power solutions offer other features, including compliance with Section 33.7.1 of the IEEE802.3at-2009 standard, which requires all PSEs to meet the International Electrotechnical Commission 60950-1:2001 specification, including classification as a limited power source with power not exceeding 100 VA (or 100 W) per port, without the need for special overcurrent protection devices. HDBaseT also performs detection and classification of powered devices, which can determine the power consumption of a device before power is applied.

As the industry moves to higher powers, other standards are emerging. For example, HDBaseT-powered TV and audio equipment must comply with UL 60065, which requires a flame-retardant enclosure when the load is greater than 15W. Therefore, even if a TV load meets the IEC 60950-1:2011 requirement for limited power less than 100W/port, it still needs to use a flameproof enclosure.

When the demand for limited power shifts to implementations above 100W/port, the cable is required to be connected to the PSD and the input of the power supply device using a special flame retardant tube through a bracket-mounted metal box. This requirement applies to cable lengths greater than 10 feet (3.05 meters).

Figure 1 This circuit has two ports, each carrying 100W. The power is calculated at the powered device end, and each port has a power limit requirement. According to the US Electricity Regulations, multi-port midspans that use this solution to power devices must have a nameplate at each port stating the rated power.

For cables shorter than 10 feet, designers can use the same four-pair POE/HDBaseT cable system, which includes a data cable and an RJ-45 plug. However, the characteristics of this cable must exceed the requirements of typical Category 5/E cable (Figure 1). Some manufacturers try to get around the 100W cap and the associated protection requirements by suggesting that the cap can be applied to each of the two PSEs within a cable. Using this logic, they believe that a compliant PSE can support 95W, and a PSE pair can support approximately twice that amount on the same cable. But this concept is incorrect and dangerous.

The IEEE802.3at-2009 standard specifies that the upper limit of the power supply of a 100W limited power supply be measured at the physical connector. Tables 2B and 2C of UL CAN/CSA-C22.2 60950-1-07 and the UL 60950-1 document clearly define the limits for power supplies with and without overcurrent devices (Tables 1 and 2). From a UL point of view, it is inappropriate to have two PSEs on one current because it is an in-box power supply using a single connector, which is the only connector that outputs power, and it must not exceed 100W.

Figure 2 These circuits achieve 250W over cables longer than 3.05m (a) and shorter than 3.05m (b).

The only way to achieve 250W or 250VA is to either use a circuit breaker or fuse at each port or have a qualified electrician run the cables, which virtually eliminates the benefits of deploying POE technology. Figure 2 shows the correct configuration for delivering more than 100W of power (e.g., 200W for two single ports) over all wires.

For information data equipment or TV and audio equipment greater than 15W, if the total power supply load is greater than 100W, a metal enclosure is required in both cases. The situation in Figure 2a requires a non-standard wiring structure to ensure safety. The solution cannot use RJ-45 connectors directly at the PSE and the input of the power supply device, and a qualified electrician is required to install it. The situation in Figure 2b can use a typical POE/HDBaseT wiring system, but special wiring is also required. In summary, according to the standards of the American Electrical Code, it is unsafe to use a standard Ethernet wiring structure to provide more than 100W of power with a single port.

Figure 3 HDBaseT uses all four wire pairs of the Ethernet cable to provide two power interfaces for the powered device, thus providing twice the power of the two-pair solution.

Four-pair power supply

HDBaseT achieves high-power delivery capabilities while maintaining full standards compliance by adopting the mechanism for four-pair power delivery in the IEEE802.3at-2009 specification. Four-pair power delivery provides greater power while achieving higher efficiency. It provides two power interfaces for powered devices, so that all four pairs of Ethernet cables can be used to obtain twice the power of the two-pair solution (Figure 3). Of the two power interfaces, one uses two pairs of wires 1, 2, 3, and 6, and the other uses two pairs of wires 4, 5, 7, and 8. This structure can increase the energy provided and fully comply with the standard. In a typical HDBaseT implementation, a 50 to 57V-dc power supply is installed to power the PSE, and all powered devices are powered directly through the HDBaseT link on Category 5 or higher cables.

Table 1 Power supply limits without overcurrent protection devices

Output voltage Output current Surface power

a UCC: Output voltage is measured in accordance with 1.4.5, with all load circuits disconnected. Voltage is continuous sinusoidal AC and ripple-free DC. For non-sinusoidal AC and DC with ripple greater than 10% of the peak value, the peak voltage shall not exceed 42.4V.

b ISC: Maximum output current without any capacitive load, including a short-circuit circuit.

c S(VA): Maximum output VA without any capacitive load.

d If the protection comes from an electronic circuit or a positive temperature coefficient device, measure ISC and S 5 seconds after the load is applied, otherwise 60 seconds.

Table 2 Power supply limits with overcurrent protection devices

Output voltage Output current Surface power Rated current of overcurrent protection device

a UCC: Output voltage is measured in accordance with 1.4.5, with all load circuits disconnected. Voltage is continuous sinusoidal AC and ripple-free DC. For non-sinusoidal AC and DC with ripple greater than 10% of the peak value, the peak voltage shall not exceed 42.4V.

b ISC: Maximum output current without any capacitive load, including a short circuit, measured for 60 seconds after the load is applied.

c S(VA): Maximum output VA without any capacitive load, measured for 60 seconds after the load is applied.

d During the measurement, the current limiting impedance is maintained in the circuit, but the overcurrent protection device is bypassed. Note: The reason for bypassing the overcurrent protection device during the measurement is to determine the amount of energy that may cause overheating during the operation of the overcurrent protection device.

e Rated current of overcurrent protection device: When the current is equal to 210% of the rated current specified in the table, the current of the circuit fuse and circuit breaker will be cut off within 120 seconds.

When using HDBaseT, the core POE technology uses 1A of current on each of the two cable pairs and uses a three-event classification method to determine the PSE that complies with the standards. This scheme enables HDBaseT technology to transmit up to 100W of continuous DC power per port from one end of the HDBaseT link to the other. The HDBaseT power supply standard goes a step further than IEEE802.3at-2009, which enables the powered device to identify the cable length and impedance and provide more power when necessary as long as the total power consumption does not exceed 100W. HDBaseT can use a single LAN cable to provide up to 100W of power over a distance of 100m without the need for an additional power supply, which is in line with trends in energy use and demand, as well as government-led efforts to improve energy efficiency. This power level exceeds the requirements to support today's typical 40-inch LED TV, which requires 70W of power.

Table 3 Proposed version 6.0, effective summer 2012 (viewable screen area)

This year, the U.S. Environmental Protection Agency's latest Energy Star 5.3 specification will limit all TVs to 108W, regardless of screen size, while Energy Star 6.0 aims for 85W or less for all screen sizes. Table 3 shows the proposed 6.0 power specification, which should go into effect this summer (Reference 1). Both LCD and LED TVs should soon consume about 1W per inch of screen. At this level, the HDBaseT power specification can support even larger displays.

Although today’s Ethernet switches can and often do have built-in POE technology, another energy-efficient approach is to deploy POE midspan, which sits between a non-POE switch and a network-powered device. Midspan is also the preferred deployment model for HDBaseT, because adding 100W to each port of an Ethernet/HDBaseT switch would be a daunting task and would greatly reduce system reliability. The midspan approach also enables remote power device monitoring and configuration, which significantly reduces power consumption. Network administrators can monitor power consumption per port and total power consumption, and configure instant on/off and scheduled on/off functions for ports, as well as on/off functions for uninterruptible power supply status ports.

POE technology can also improve energy efficiency by minimizing idle power consumption. Many POE midspans and switches use switching power supplies that are 90% efficient at full load, meaning a 220W POE power supply consumes 220W of AC energy, while a 400W POE power supply consumes 440W. Unfortunately, when a 200W-rated unit switching power supply is idle, the switching power loss at 0W load is 20 to 40W, while a 400W-rated unit loses 40 to 80W at 0W load. This problem can be solved by adjusting the distributed power structure of POE. For example, a network administrator can start with a 450W internal power supply to handle all real-time needs, and then upgrade to full power per port with an external 450W to 1 kW power supply when necessary.

Another important area of ​​POE innovation is the extension of distance. Four-pair power can power devices with up to 100m of cable, which is the distance defined by the HDBaseT standard. Today's POE midspan measures the cable length from the middle, and when the cable length and the maximum power demand of the device are known, power can be correctly provided to the powered device. This solution ensures that a powered device that requires more than 22.8W of power at a distance of 100m will not accidentally lose power when it reaches maximum load.

Figure 4 The obtained baseline distance extension

Power of the powered device at 200m from the PSE source

Four-pair IEEE802.3at PSE (60W) 25W (802.3at powered device) 12.95W (802.3af powered device) 12.3W (802.3af Class 2 powered device)

Network administrators can use extender technology to simultaneously provide data and power to network devices such as WLAN access points and network cameras at a baseline distance of 200m, which is twice the distance of the IEEE specification. The extender device is simply connected to a midspan and receives power through the POE input. Table 4 shows the extended baseline distance. In addition, cascading can be done to achieve longer distances.

POE is constantly evolving, providing more high-value power supply and management functions. As the technology moves beyond the 60W limit and has a new generation of higher power capabilities, the key point for designers is to maintain compliance with all IEEE802.3at-2009 standards, including standards to ensure safe power supply. The HDBaseT Alliance has adopted IEEE802.3at-2009 as the 100W technology, which fully supports all safe power supply requirements and provides the opportunity to aggregate uncompressed high-definition digital video, audio, 100BaseT Ethernet, standardized power supply, and various control signals on a single 100m 5e/6 category cable.