PoE Powering Efficiency

PoE Powering Efficiency

Without PoE, deploying necessary technology like the humble office phone, WiFi access points and IP cameras attracts high initial costs. Introducing higher future costs when reconfiguring the network, device locations supplying individual power and communications cabling varies building extremities. PoE, on the other hand, substantially reduces the cost of building large-scale smart cities, road and rail infrastructure by combining both power and Ethernet in one cable, but it’s not without its limitations.

The PoE standard IEEE 802.3af was introduced 20 years ago, defining the voltage and current transmission practice over Ethernet. Well known for powering phone handsets of up to 15 watts via a technology called VoIP (Voice over Internet Protocol), it wasn’t until advancements in WiFi and IP Camera technology that PoE become more useful than just powering the limited growth communications handset. The majority of devices however require more than 15 watts for their intended application, and in this era of ever-increasing need to be omni connected, PoE 802.3at was birthed in 2009. This effectively doubled the available power in Ethernet cables to 30 watts.

Today, the natural evolution is to extend these power limiting factors to unleash further PoE applications. Enter the recent release of IEEE 802.3bt POE standard, which provides power over four pairs to achieve 100 watts over 100 metres of cable and increases the network communication speed to 10Gbs. Infact, the standard applies to both type 3 (previously known as PoE++) and type 4 into the ruling, defining support for a maximum of 60 watts and 100 watts, respectively.

However beware: PoE 802.3bt now includes two types of power classes and not all devices have the grunt to support Type 4 100 watts of power over 100 metres of Cat5e cable. Additionally, PoE 802.3bt level is expected to be the maximum level defined, as higher levels may not be safe for the existing cabling and connectors deployed in today’s infrastructures.

Cabling manufacturer Belden is paving the way forward in advanced Ethernet cabling and its new RJ45 connector design caters for such an increase in power draw.

Through testing and development, Belden has a proven new CAT6A cable that out performs the competition over a wide climate temperature span, while reducing the insertion loss to maintain promised performance levels.

The new standard extends the power classification information exchanged during initial negotiation to allow for meaningful power management capability, whilst being intelligent enough to support multiple PoE classes and is backward compatible. Support for devices connected to the Ethernet network include PTZ security cameras, kiosks, POS terminals, thin client, 802.11ac and 802.11ax access points, small cells, and connected LED lighting, all of which can benefit from PoE.

The new standard not only future proofs infrastructure, but comes with a host of improvements for PoE, with a focus on energy efficiencies that reduce power usage from the older PoE standards.


MPS: Low power and efficient

Consider deploying a large number of PoE devices with standby power. IEEE 802.3bt removes the AC MPS requirement and improves the previous standard by 10 times less power drawn for low power devices. An example is LED lights where the onboard Ethernet port is kept alive while the lamp is in the off state, resulting in less than 20 mW consumed. Multiply this by the number of ports in the system, and results show significant power savings to keep PoE devices in standby mode.

Autoclass: Smart sensing

Autoclass is a classification mechanism that allows PoE devices to communicate at its maximum power consumption. It effectively measures the power consumption of the connected device throughout a defined period. The PoE source then sets the maximum power output based on the power drawn during auto class, plus margin.

Extended power: Free up available power
PoE devices are connected from as little as a few metres to 100 metres from the powered source. Therefore, budgeting for the maximum power losses is wasting system power. The extended power feature calculates the maximum available power based on the cable’s true total resistance. This means an accurate power budget is obtained per device, freeing total system power to other ports, while also being more efficient with its available power.

4Pair capable: Dual purpose
An IEEE 802.3bt compliant device will identify the PoE device type and set the power accordingly to a Single-Signature PD or Dual-Signature PD supply. Dual-Signature PDs allow for the support of two independent loads, each with different power classes. For example, in a surveillance camera built with Dual-Signature PD, one pair may be connected to the camera and the other pair may be connected to the heater.