Cabling Strategy for Power over Ethernet (PoE)

Power over Ethernet (PoE) is a technology for implementing wired Ethernet local area networks (LANs) that enables the electrical current necessary for operating each device to be carried by Ethernet data signal cable or twisted copper cable (UTP). Signaling was sent on one or two of the four pairs of UTP cables, and power was transmitted on the remaining two pairs. The Electric power can be supplied from the Power Sourcing Equipment or PSE, which may be a PoE Switch or through PoE Midspan such as a PoE Injector device

Figure 1 Power Over Ethernet technology

Basically, there are many devices that apply PoE technology such as :

Figure 2 IP Camera connection using stranded copper cable (UTP)

(illustration from www.ddproperty.com)

PoE Type & IEEE Standard

           PoE Type 1, also known simply as PoE or 2-pair PoE, comes from the original IEEE 802.3af standard that came to completion in 2003. Type 1 PoE uses two pairs to connect several different types of lower-powered devices to a network. When utilizing PoE Type 1 it can provide 15.4W, 48V,350mA (min.44V and up to 54V) of DC power to each PoE port and up to 12.95W of power for each device. Examples of devices that PoE Type 1 can support include static surveillance cameras, wireless access points, and VoIP phones.

           Like PoE Type 1, PoE Type 2 also utilizes 2-pair PoE. Its basis is the PoE+ or IEEE 802.3at Ethernet standard, which the Institute of Electrical and Electronic Engineers released in 2009. As such, it delivers up to 30W of power at the port level over an Ethernet twisted pair cable and up to 25.5W of power or as much as 50 Watt and provides a voltage from 42.5V – 57V to each device. It connects higher-powered devices to a network such as PTZ cameras, RFID readers, Wireless Access Point, video IP phones, and alarm systems. The maximum current that can be supplied by the PoE+ Switch is 30 Watt. Because it is backward compatible, however, it can support the types of devices typically supported by PoE Type 1 as well as devices supported by PoE Type 2. It supports Cat 5 cables or better.

           Later in 2018 The IEEE 802.3.bt or PoE++ standard has been defined. PoE++ can be classified into 2 Types: Type 3 that uses 4 pairs of cables to supply 51 Watt power and Type 4 that uses 4 pairs of cables to Supply 71 Watts of power, PoE++ network switch is the next generation of PoE+ technology. PoE++ switch supports up to 60 watts of power to each port under Type 3 and offers the highest level of power for Power over Ethernet switches -- up to 100W on each PoE port under Type 4.  Type 4 PoE can support extremely power-hungry devices such as laptops and flat screens.

Figure 3 Type of PoE and IEEE Standard

The Advantage of PoE

There are many advantages of power over Ethernet. For example, PoE allows professionals to install remote or outside equipment without connecting to AC power to deliver power to several locations without installing additional electrical infrastructure or several power outlets. PoE is also highly cost-effective as it allows you to use one cable for both power and data transmission, so paying to purchase and run multiple cables isn’t necessary. In addition, PoE makes it easier to expand and install a network and is also highly efficient and responsive. PoE can power devices located in ceilings, rooftops, lampposts, fence lines, pipelines, transportation lines, and other places The cost of carrying electrical power to individual devices is eliminated by supplying power to devices over Unshielded Twisted Pair (UTP) signal cables.

The benefits of PoE can be summarized as follows.

Cost savings: Since PoE eliminates the need to be tethered electrical outlets, devices such as security IP cameras and wireless access points can be located where they are needed most and repositioned more easily. PoE allows users to add devices in awkward or remote locations. In many cases, PoE can be a safer alternative because it is designed to protect network equipment from electrical overload, under-powering, or incorrect installation.

Flexibility: Can easily expand a network even when power is problematic. They are easy to maintain and checked - you can monitor them remotely. You do not need an electrician to wire them in because they don't need wiring.

Simplicity: Install only the signal cable to the end device. Reduce cable clutter and save space.

Safety: PoE uses relatively low voltages, so there is low risk of electrical hazard.

Reliability: PoE devices are in full compliance with the IEEE 802.3 standard that defines standards for Ethernet networks.

Functionality: Endpoint devices can be reset remotely.

PoE Mode

PoE operating method can be classified into two modes:

There are two modes of PoE, A and B. Mode A delivers power on the data pairs of 100BASE-TX or 10BASE-T. Mode B delivers power on the spare pairs. PoE can also be used on 1000BASE-T Ethernet, in which case there are no spare pairs and all power is delivered using the phantom technique.

In mode A, pins 1 and 2 form one side of the 48 VDC, and pins 3 and 6 form the other side. These are the same two pairs used for data transmission in 10BASE-T and 100BASE-TX, allowing the provision of both power and data over only two pairs in such networks. The free polarity allows PoE to accommodate for crossover cables, patch cables and auto-MDIX.

In mode B, pins 4–5 form one side of the DC supply and pins 7–8 provide the return; these are the "spare" pairs in 10BASE-T and 100BASE-TX. Mode B, therefore, requires a 4-pair cable.

The PSE (power sourcing equipment), not the PD (powered device), decides whether power mode A or B shall be used. PDs that implement only Mode A or Mode B are disallowed by the standard.

10Base-T and 100Base-TX transmissions may work in either mode, but 1000Base-TX or Gigabit Ethernet only operate in Mode A,  because Gigabit Ethernet requires both cables. The PSE (Power Sourcing Equipment) will decide which mode to choose to work in. The PD devices are not allowed to choose such mode or both modes at all electrical power is transmitted over a data pair using the following four methods.

The 10/100 and gigabit Ethernet cables have four pairs of twisted cables that correspond to 8 pins. The 802.3af standard established that for 10/100 Ethernet cables only two of the four pairs of wires are permitted to transmit data, while the other two could be used for power. Of these pairs, 10/100 Ethernet only allows for the transmission of data over two wire pairs (four wires)

1. 10/100BASE-T Mode A:

Position positive DC power on signal pins 1 and 2 and negative DC power on signal pins 3 and 6 in Fast Ethernet. These are also used as coaxial cables for data transmission. so information This "sharing" of wires is accomplished using a technique known as phantom power, which was originally used as a way to transmit DC power through microphone cables to power microphones with Active electronic circuitry.

Figure 4. PoE feeding using 10/100BASE-T Alternative A

2. 10/100BASE-T Mode B:

Position positive DC power on signal pins 4 and 5 and negative DC power on signal pins 7 and 8 in Fast Ethernet. These pairs are "spare" pairs, so power is not shared with data, and there is no phantom power.