95 W Power over Ethernet

Important note for readers: This article relates solely to PoE power supply with active end-point detection. It deliberately does not cover passive PoE power supply, which is often used by internet service providers to power wireless routers. The main disadvantages of passive solutions are as follows:

  • Inability to detect end devices (the source does not know whether the device at the end of the cable is PoE-compatible).
  • Inability to centrally monitor the power supply system using the SNMP protocol

PoE offers enormous advantages thanks to its minimal cabling requirements. Unlike conventional power supply systems, it does not require separate cables for data and power. Furthermore, communication between the power source and the powered device ensures protection against short circuits and, last but not least, enables easy monitoring of the entire power supply system via the SNMP protocol.

Since the ratification of the first PoE standard in 2003 (IEEE 802.3af), its use has expanded significantly into a whole range of new applications. Over time, however, it has become apparent that its limiting factor is the maximum rated power of 15.4 W per port. Whilst this power was sufficient for standard fixed cameras and IP telephones, it proved limiting for IP cameras with IR illumination, PTZ cameras, video phones and other devices. Depending on the pairs used for power transmission, the standard distinguishes between PoE Mode A (via data pairs) and PoE Mode B (via spare pairs). According to the standard, every PoE-PD (Powered Device) should support both modes, A and B. In practice, however, camera manufacturers sometimes try to cut costs by fitting only components for PoE A. For PoE-PSE (Power Supply Equipment) devices (PoE switches and injectors), support for just one mode is sufficient. However, all our LAN-RING BOX series switches support both modes A and B.

For this reason, the IEEE published a new standard, IEEE 802.3at, in 2009, with a power output of up to 30 W per port. According to the standard, every PoE-PD (Powered Device) should again support both modes, A and B.

However, development has progressed rapidly. The market has seen a proliferation of outdoor PTZ security cameras, POS terminals, LED lighting, 802.11ac and 802.11ax access points, and other devices that require more than 30 W to operate. High demand typically leads to a battle between different standards. The IEEE continued its work on a new standard, which was ratified in September 2018 as IEEE 802.3bt, with a maximum power output of 90 W per port. However, as early as 2011, the HDBaseT Alliance had developed the Power over HDBaseT (PoH) standard, which enables a maximum power output of 100 W to be delivered over four pairs of Cat5e cable.

The result of this process is two mutually incompatible power standards: 90 W PoE according to IEEE 802.3bt and 100 W PoE according to the HDBaseT Alliance’s PoH. All METEL LAN-RING PP switches with the 2020 hardware version support both solutions; see the table below.

LAN-RING PP / 2020 hardware version – overview of supported PoE power modes
Type Standard Maximum PoE-PSE power output Maximum power consumption for PoE-PD
 Cable category Cable length Number of pairs for power transmission
 Minimum input voltage for PoE PD
1 802.3af 15.4 W 12.95 W Cat5e 0–100 m 2 37 V
2 802.3at 30 W 25.5 W Cat5e 0–100 m 2 42.5 V
3 802.3bt 60 W 51–60 W Cat5e 0–100 m 4 42.5 V
4 802.3bt 90 W 71–90 W Cat5e 0–100 m 4 41.1 V
POH POH 95 W 95 W Cat5e 0–100 m 4 38.125 V

 

UPOE

These are essentially two separately detected and classified Class 4 devices. Typical examples of UPOE include outdoor PTZ cameras with PoE heating or fixed cameras in enclosures with PoE heating.

PoE power supply according to IEEE 802.3bt

Transmitting high power over UTP/FTP/STP cables places increased demands on their quality. Therefore, to ensure correct operation, only cables with copper conductors of Category 5 or higher should be used. For example, CCA cables with aluminium-core conductors and a copper coating are completely unsuitable. For convenience, the following table shows the results of calculations for power and voltage losses for various input voltages and cables.

The calculation also demonstrates the advantage of a higher input voltage. For this reason, in OH switchboards we use power supplies with a regulated output in the range of at least 48–56 VDC.

Approximate calculation of losses for Cat5e CCA cables with a conductor resistance of 130 ohms/km.
Distance between PoE PSE and PD PoE PSE output voltage Power supplied by the PoE PSE Total loop resistance Current flowing through a loop Line losses PoE-PD input voltage Minimum PoE-PD input voltage according to the standard
10m 56 V 90 W 0.65 Ω 1.61 A 1.04 V / 1.68 W 54.96 V 41.1 V
10 m 48 V 1.88 A 1.22 V / 2.29 W 46.78 V
100 m 56 V 6.5 Ω 1.61 A 10.45 V / 16.79 W 45.55 V
100 m 48 V 1.88 A 12.19 V / 22.85 W 35.81 V

 

Approximate calculation of losses for solid-core Cat5e cables with a conductor resistance of 93.8 ohms/km (BELDEN 1594A)
Distance between PoE PSE and PD PoE PSE output voltage Power supplied by the PoE PSE Total loop resistance Current flowing through the loop Line losses PoE-PD input voltage Minimum PoE-PD input voltage according to the standard
10m 56 V 90 W 0.47 Ω 1.61 A 0.75 V / 1.21 W 55.25 V 41.1 V
10 m 48 V 1.88 A 0.88 V / 1.65 W 47.12 W
100 m 56 V 4.69 Ω 1.61 A 7.54 V / 12.11 W 48.46
100 m 48 V 1.88 A 8.79 V / 16.49 W 39.21 V

 

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PoE power according to the HDBaseT Alliance

The POH power supply standard was published by the HDBaseT Alliance as early as 2011. It is based on the IEEE 802.3at standard and enables the safe transmission of up to 100 W over an Ethernet cable. It was published many years before the competing IEEE 802.3bt standard, so, in addition to many audiovisual devices, it is used by the vast majority of IP cameras with a power consumption exceeding 25.5 W.

Approximate calculation of losses for Cat5e CCA cables with a conductor resistance of 130 ohms/km
Distance between PoE PSE and PD PoE PSE output voltage Power supplied by the PoE PSE Total loop resistance Current flowing through the loop Line losses PoE-PD input voltage Minimum PoE-PD input voltage according to the standard
10m 56 V 95 W* 0.65 Ω 1.7 A 1.10 V / 1.87 W 54.9 V 38.13 V
10 m 48 V 1.98 A 1.29 V / 2.55 W 46.71 V
100 m 56 V 6.5 Ω 1.7 A 11.03 V / 18.71 W 44.97 V
100 m 48 V 1.98 A 12.86 V / 25.46 W 35.14 V

 

Approximate calculation of losses for solid-core Cat5e cables with a conductor resistance of 93.8 ohms/km (BELDEN 1594A)
Distance between PoE PSE and PD PoE-PSE output voltage Power supplied by PoE-PSE Total loop resistance Current flowing through the loop Line losses PoE-PD input voltage Minimum PoE-PD input voltage according to the standard
10m 56 V 95 W* 0.47 Ω 1.7 A 0.8 V / 1.35 W 55.2 V 38.13 V
10 m 48 V 1.98 A 0.93 V / 1.84 W 47.07 V
100 m 56 V 4.69 Ω 1.7 A 7.96 V / 13.5 W 48.04 V
100 m 48 V 1.98 A 9.28 V / 18.37 W 38.72 V

* 95 W is the maximum power supported by PP switches with hardware designed in 2020.

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