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.

Figure 5.  PoE feeding using 10/100BASE-T Alternative B

3. 1000BASE-T Mode A:

Position positive DC power on signal pins 1 and 2 and negative DC power on signal pins 3 and 6. In Gigabit Ethernet, all 4 pairs are supplied, so phantom power is always required for Gigabit PoE.

Figure 6.  PoE feeding using 1000BASE-T Alternative A

4. 1000BASE-T Mode B:

IEEE 1000BASE-T Option B Position positive DC power on signal pins 4 and 5 and negative DC power on signal pins 7 and 8.

Figure 7.  PoE feeding using 1000BASE-T Alternative B

The communication between the PSE device (Switch) and the terminal device (PD) has the following steps.

PSE (Switch) Checks the condition of the UTP cable connected to the PD. If the status is normal, the PSE starts supplying power to the PD.

PD starts working.

The PD sends a PSE (Hello Message) signal saying "I am a PD, require a maximum power of xxx Watt.

PSE replied to PD, “I am PSE, I can give you the maximum power xxx Watt.”

The PD may not use the maximum power that the PSE can provide.

The rules for this power negotiation are:

PD shall never request more power than physical 802.3af class

PD shall never draw more than max power advertised by PSE

PSE may deny any PD drawing more power than the max allowed by PSE

PSE shall not reduce power allocated to PD that is in use

PSE may request reduced power, via conservation mode

Selection Criteria of Cables for Power over Ethernet (PoE) Transmission

Figure 8. Cable selection for PoE applications.

A safe PoE operation is an outcome of different combining factors. There are five important factors: temperature ratings, conductors, cable material, cable design, and installation mechanism. A slight deflection in any of these fundamental factors can lead to an efficiency drop in the PoE transmission network. Consideration of the following factors while selecting cables for Power over Ethernet (PoE)

Temperature Rating: The temperature rating means the highest amount of temperature that can be sustained by the cable’s jacket or shielding. The cables for PoE transmission should have more than 60˚C of temperature rating. A higher temperature rating is essential as the higher the temperature rating, the higher is the power dissipation via the copper cable. Therefore, while selecting cables for Power over Ethernet (PoE), the temperature rating of the cable must be checked. Commonly PoE cables with 60˚C, 75˚C, and 90˚C are the temperature ratings available in the market. However, temperatures over 200˚C of temperature rating can be achieved in PoE cables.

Size of a Conductor Gauge: The conductor resistance is one of the factors responsible for heat generation in PoE cables. The conductor resistance is higher in small gauge diameter cables, which generate a high amount of heat. Thus, the purpose behind checking for a conductor gauge size is to reduce heat generation or increase heat dissipation through the cable body. To achieve this, a larger connector gauge diameter must be selected. A connector with a larger diameter increases the heat dissipation across the length of the PoE cable. The heat is generated due to connector resistance or insertion losses, and the generated heat is dissipated throughout the cable.

It is always ideal to choose CAT6 or CAT6A PoE cables instead of CAT5e cables. CAT6 cables are known to have about 80% lesser connector resistance (DCR) as compared to the CAT5e cables. Therefore, cables with a larger diameter, lesser conductor resistance, lesser heat generation, and higher heat dissipation must be considered for PoE applications.

Cable Construction: The construction of copper cables contributes to heat generation and dissipation.

There are two common types of copper cable construction, namely, unshielded twisted pair cable (UTP) and shielded twisted pair cable (STP). Generally, STP cables with foil or metallic shields are known to offer higher heat dissipation than UTP cables. The higher the heat dissipation, the cooler is the cable. Therefore, selecting a category 6 or category 7 STP cable with foil or metallic shields are advised.

Installation Mechanism: The type of installation or connectivity mechanism of the copper cable determines thermal resistance and insertion losses. The installation configuration is expected to have low insertion loss, easy connectivity, and a good heat dissipation factor. Inappropriate use of installation mechanisms can result in conduit effect, and trapped heat which can further damage the physical and operational performance of the cable.

Cable Material: When it comes to selecting a PoE cable, one can get two common choices, namely, copper clad aluminum (CCA) and pure copper cable. The pure copper cable has been traditionally used in PoE applications and is expensive. The copper-clad aluminum cables are economic, however, these cables may lead to interruptions during PoE transmission due to inferior materials used. The copper-clad aluminum cables generate high resistance, which leads to radiant heat generation in the long run. On the other hand, pure copper cables offer less resistance and less heat generation, therefore, it can be used for a longer run without any impact on data transmission speed. Selecting the correct cable material for the PoE applications can help in enhancing PoE transmission efficiency.

Link's cables, whether CAT5E, CAT6, CAT6A, are manufactured according to ANSI/TIA standards and tested by UL.

Figure 9 Structure of the signal cable.

Figure 10. Link's CAT5E, CAT6, CAT6A cable.

US-9015LSZH: CAT 5E UTP Enhanced CABLE (350MHz), LSZH, White

US-9106LSZH: CAT 6 UTP (250 MHz) w/Cross Filler, 23 AWG, LSZH

US-9266LSZH: CAT 6A F/UTP XG (650 MHz) CABLE, LSZH, Aqua Blue

Why CCA is not suitable for PoE

Copper Clad Aluminum (CCA) 

Figure 11. Copper Clad Aluminum (CCA) signal cable.

(Illustration from https://generalclad.en.made-in-china.com)

CCA cable is a cable with an aluminum core and a copper coating around it. Cables made with CCA conductors do not have a valid safety listing per the National Electrical Code (NEC), and can’t be legally installed into areas of buildings that require CM, CMG, CMX, CMR or CMP rated cables, according to CCCA (Communications Cable & Connectivity Association). The concerns of installing these types of cable can be slower network performance and a possible safety hazard.

Figure 12. Copper Clad Aluminum (CCA) cabling structure.

(Illustration from http://gapcable.com)

CCA cable does not work well for cabling PoE infrastructure or PoE High Definition IP Cameras as it has about a 50%-60% higher DC resistance in comparison to pure copper wire. Due to the increased resistance neither the data signal nor power are able to travel as far or at the same quality as they would in a pure copper wire. Furthermore, this issue is sure to be compounded as we see a higher emergence of PoE Plus applications.

Figure 13. Image showing damage caused by using CCA cable.

Solid CCA cables are even less flexible than solid copper cables due to the inelasticity of Aluminum compared to copper. Aluminum is not only less flexible; it also is less conductive. Meaning, more signal (or signal packets) may be dropped or lost during the transition, which is why CCA cables should not be used for an application that requires high signal quality.

Figure 14. PoE-optimized cabling installation

(Illustration from www.hooyae.com)

Therefore, installing cables that are suitable for PoE work should be the cables that comply with TIA standards with 100% solid copper conductors.

In addition, to select the cables, the power of the terminal equipment must also be taken into account. For example, if the terminal equipment requires high power, it should choose a signal cable with large copper conductors such as CAT6 or CAT6A, etc.

Figure 15. Implementing PoE

Challenges in PoE Technology 

Aftereffects of Power Fluctuations – The power fluctuations or constant loss of electric supply can be problematic at times. It may lead to a reboot of the systems and adversely affect the system-based activities. Consequent to errors in the power, the system may appear shut down and stop functioning altogether.

Defects in Cabling – Perfect cabling is mandatory for the PoE to perform continuously. The defects in cabling, including short circuit, open cabling, or split pairs can disrupt the functioning.

Eliminate Unwanted Power Factors – Filtering out the factors that can hamper the operation of PoE is essential. Induced power problems from attached devices can falter the system. Or any external impulse such as a thunderstorm can overload the servers and can result in cascading effect/ complete failure.

Improper Installation and Non-compliance of Laid Down Standards – Some manufacturers may consider following the standards derived by them. They may not consider the standard formulated by IEEE. It may turn problematic for your network/ power systems. Moreover, improper configuration/ installation and unproven system spec can affect the functioning.

Overheating Issues – The power requirements have increased largely over a period. It has become more than double, from the maximum limit of 30W earlier. Consequently, four pairs of cables have to be used in place of two, causing overheating of the cables.  This will adversely affect performance, besides being a safety hazard.  However, this problem could be resolved by observing the following measures

Safety

The PSE must not damage the existing cabling infrastructure or the connected unpowered devices, so it must only be powered when a PoE-enabled endpoint is detected and must be terminated quickly. After physical disconnection, the PoE system must be protected from overload and short circuit. PSE ports must be protected from cross-connection to adjacent ports. In addition, thermal protection should be provided to avoid ignition.

Distance

In accordance with ANSI/TIA/EIA standards for Category 5E (CAT5E) (TIA568.2D) cabling, the maximum length for the cable section is 100 m (328 ft). The PSE Power Injector is especially mid-span. The distance of the data network should not be increased. For example, the wiring of the peripheral signal exceeds the cable length limitation.

Figure 16. Shows the UTP wiring distance limit under PoE.

A common solution to overcome the distance and bandwidth limitations of copper cables is to use fiber optic cables. Due to the inability to deliver DC power over fiber, a PoE Media Converter, acting as a PSE, is used to power the RJ-45 port, PoE Media Converter converts fiber to copper and delivers DC power to the PD via UTP cable.

Figure 17. using Fiber Optic switch port with PoE Media Converter to overcome distance limitation.

Summary

CCA cable is not suitable in any way for PoE (Power Over Ethernet) due to the conductors themselves heating up and potentially starting a fire (called DC resistance), or damaging a PoE device on the other end due to the inability to supply enough current. 

Link's signals such as CAT5E, CAT6, CAT6A are designed and manufactured to Complies with ANSI/TIA standards and tested by UL Institute. Suitable for PoE application, whether installing CCTV or Wireless Access Point without affecting or damaging the network equipment. or harm the users