PoE Standards for IoT Devices and Power Sourcing Equipment
In this Industry Article, we'll discuss PoE (Power over Ethernet) standards and power sourcing equipment (PSE), using office Internet of Things (IoT) devices as an example application.
The increase in the number of IoT devices has also increased the adoption of PoE.
Examples of PoE powered devices (PDs) include:
- Lighting and digital signage
- Computer displays and video conferencing systems
- Door access, security cameras, and fire alarm systems
- Telephones and phone charging stations
- PoS (point of sale) systems
- Internet access points
PoE IoT devices can be powered through LAN (local area network) cable so that no separate power supplies or power sources are required. LAN cables can safely provide both power and data for IoT devices without the need for long power cables.
PoE devices can be used anywhere where there is an Ethernet port. Other technologies, including USB, have significant signal and power losses over long cables. These limitations are less of a concern with PoE devices and cables.
PoE simplifies both the setup and usage of these IoT-powered devices.
Understanding PoE Standards and Cables
Understanding each of the PoE standards (see Table 1 below) is crucial to designing PoE applications. The Institute of Electrical and Electronics Engineers (IEEE), governs the PoE (IEEE 802.3af), PoE+ (IEEE 802.3at) and PoE++ (IEEE 802.3bt) standards.
Table 1. Institute of Electrical and Electronics Engineers (IEEE) PoE Standards
PoE PSE utilizes signal pairs within a Cat 3 or Cat 5 cable to provide power to PDs. The other pairs may be used for data or remain unused. PoE+ uses a Cat 5 or higher cable as it has four (4) twisted pair cables as compared to two (2) in a Cat 3 cable. This provides more power, data, and reliability to the PD.
For example, some PoE devices, such as a controlled lighting network, digital signage, and video conferencing applications demand higher power.
The PoE+ standard can provide significantly more power than PoE devices in some applications. This is done through standard Cat 5 or higher Ethernet cables with data rates of 10 Mbps, 100 Mbps, 2.5 Gbps, 5 Gbps, or 10 Gbps.
PoE++ provides even more power and data through Cat 5e and Cat 6 cables and is most often employed in PSE.
The 802.3bt PoE (PoE++) standard is designed for four pairs of cables to supply higher power devices with up to 60 W for Type 3 and 100 W for Type 4. As a result, it allows for nearly three times the power delivery over Ethernet cabling than previous standards and ten times the data transmission rates permitted by the 802.3af PoE standard, making it ideal for high power office applications such as video conferencing.
Applications for PoE Devices
Once the various PoE standards are understood, consider how individual devices will be utilized. In an office setting, many devices, including desktop equipment such as IP-based phones, will need to be moved frequently.
On the other hand, PoE lighting and access and security equipment must remain stationary but may need to transmit power over long cables in order to operate effectively. These use models and their unique requirements must be considered during the PoE system design and installation.
Powered Sourcing Equipment in PoE
The PDs listed above are but one category of PoE devices. The second category of devices is what powers PDs: PSE.
PSEs include network switches, injectors, repeaters, and extenders that provide data, electricity, and even hardware-based security encryption for PDs. Modems and routers may fall into both categories as they are end devices but can also provide the data, power, and security for other PDs.
PSE Injectors using the PoE+ standard can provide up to 30 W of power and 10 Gbps of data to PDs. Well-designed PoE injectors will have power surge protection and thermal management built into the device to protect against spikes in power, excessive heat, and to deliver consistent power to PDs. Many PoE switches incorporate these injectors into their design in order to expand the local area network. However, because long cables are used in most office applications, PoE extenders are needed to extend the power and data signal over greater distances, enabling PDs to operate as designed.
The PSE data and power rate dictates the length of the cable required within a PoE network. Due to both the length of cables and potential electrical interference, power and data losses may occur over longer cable runs. This can be addressed by calculating the power and data losses based on the power requirements, the number of network devices, and cable length.
PSEs should be chosen to supply the required amount of power to the PDs and not necessarily be designed to employ the maximum amount of power in order to save costs and protect equipment.
Protection in PoE Systems
Specialized PoE transformers are required to protect the network and devices each time power and data are increased. While older transformers use a toroidal-shaped core, newer transformers provide greater stability and flexibility for devices through a specialized winding process.
By their very nature, different PoE devices, such as lighting, digital signage, and telephones, have very different protection requirements (see Figure 1). However, non-PoE should not interfere with PoE devices and equipment within a network because they cannot transmit or relay power. It is likely that office users will use non-PoE devices within the network.
Figure 1. Power and Protection building blocks for PoE in power sourcing equipment and powered devices
As an example, an IP-based office phone has different protection requirements than an injector, as it consumes power rather than repeats or transmits it. Depending on the usage, it may or may not need any added hardware encryption. If the phone experiences data or power signal losses or low integrity, it will be of little use to the end-user. However, it may not require the same throughput of power and data, allowing for less expensive components in the design.
In some cases, encryption is needed on data lines, and as a result, security chipsets may be needed to meet the needs of the application. While expensive, this is an essential consideration for door access, security cameras, and other office security and safety devices.
Many engineers will not have PoE design and testing experience as they require specialized equipment and expertise. Most PoE vendors work closely with distribution partners to provide needed services to engineers and manufacturers.
PDs and PSEs should be tested to ensure they meet quality, safety, and other industry standards. Also, designs should be reviewed to ensure that the design is sound and that the parts used have the maximum protection with the most cost-efficient build of materials.
All images and tables used courtesy of TDK
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