All about PoE (Power over Ethernet)

Overview
With the growing proliferation of connected devices, ranging from traffic intersection cabinets to light poles, the demand for Power over Ethernet (PoE) has surged. PoE technology allows both data and power to be transmitted through a single Ethernet cable, reducing the need for separate power sources. This article explores the benefits, technical aspects, and common use cases of PoE, highlighting its increasing importance in modern infrastructure and IoT applications. Stay informed on how PoE is transforming connectivity across industries.
The Basics and Benefits of PoE
Power over Ethernet (PoE) technology enables both power and data transmission through a single Ethernet cable, eliminating the need for separate power wiring. This simplifies installation, especially in hard-to-reach areas, and allows businesses to use existing Cat5 to Cat6a cabling without infrastructure modifications. PoE’s efficiency streamlines network setups, reducing costs and improving connectivity for devices like security cameras, access points, and IoT devices. Below shows how a PoE connection would work compared to a non-PoE connection that uses separate power and data wiring.
In a PoE application, a PSE (power sourcing equipment) provides power to a PD (powered device). A common example would be an IP camera (PD) connected to a PoE switch (PSE).

Key Benefits of PoE
- Cost and Time Savings: No need for electricians or separate power wiring, reducing installation costs and time.
- Installation Flexibility: Devices can be placed up to 100 meters from the power source, allowing for versatile setups.
- Scalability: Easily add PoE devices as needed, powered directly through network cables.
PoE Markets and Applications
Various market trend data has shown that the PoE usage continues to grow year over year.
The rapid growth of Power over Ethernet (PoE) technology can be attributed to several key factors that are reshaping the way devices are powered and managed. One of the most significant drivers is the increasing number of PoE-compatible devices. Initially used for powering IP cameras, PoE now supports a wide array of devices, including access points, smart lighting, sensors, and more. This expanded compatibility has made PoE an essential solution for a variety of industries, providing a cost-effective and efficient way to deliver both power and data over a single cable.
Another major factor contributing to the rise of PoE is the significant increase in the power it can deliver. Over the past two decades, PoE power delivery has surged from just 4W to as much as 90W, opening up new possibilities for powering more complex devices. As data speeds continue to increase, more networked devices will incorporate PoE, making it an even more attractive option for businesses. The ability to power a wider range of devices, including those requiring higher wattages, is one of the reasons PoE has become integral to modern network infrastructure.
The growing adoption of PoE has also resulted in the convergence of multiple IP devices under centralized management systems. This shift enables businesses to control various systems, such as lighting, HVAC, access control, surveillance, sensors, digital signage, Wi-Fi, and VoIP, all from one unified platform. Centralized management offers enhanced efficiency, scalability, and cost savings, making PoE a key component of smart building solutions and IoT ecosystems. As PoE technology continues to evolve, its role in powering and managing modern infrastructure will only expand, offering businesses a future-proof solution for their networking needs.

Active PoE vs. Passive PoE
As mentioned previously, PoE provides power over the same cabling used for data. There are two types of PoE protocols – active and passive. Below is a comparison table of the differences between active and passive PoE.
Active PoE provides protection for non-PoE devices that get plugged into a PoE port. If a port is passive PoE, it will provide power to the device regardless of it being PoE-enabled or not.
PoE Process
So then, how does active PoE provide power to a device that is active PoE enabled?
- When a device (PD) is plugged in, the PSE will detect if the PD has the correct resistance value to correctly categorize it as a PoE device.
- The PD will be classified to determine its rated power consumption, based on its class signature.
- During startup, the PSE will limit the inrush current with the appropriate value based on the PD class.
- The PSE will periodically perform a keep alive function with the PD to maintain operation.
- When a PD is disconnected from the PSE, the PSE must remove voltage within 15-20ms of the cable being disconnected.

PoE Standards
In the Active vs. Passive comparison table above, Active PoE is referring to IEEE 802.3af/at/bt. These are standards defined by the IEEE organization. These standards are defined by types with the amount of power that’s provided allocated per class. There are 4 types, made up by 8 classes.
802.3af = Type 1, Class 1-3
802.3at = Type 2, Class 4
802.3bt = Types 3&4, Class 5-8
The chart below shows the power that the PSE can provide along with the minimum power that the PD receives, per class.

In a cat5 or cat6 cable, there are 4 pairs of wires.
802.3af and 802.3at operate over 2 pairs of the wires. There are 2 possible modes (A and B) for the pinouts. In both modes, 4 wires are not utilized for the power portion. The diagram below shows the pinouts for both modes.

802.3bt operates over 4 pairs of wires. In this case, all 4 pairs are used to deliver power. There are 4 main improvements made in 802.3bt, compared to 802.3af/at:
- Support for Type 3 (60W) and Type 4 (90W)
- Support for dual-signature PDs. This means that a device can have two separate detection and classification circuits. This would come in useful for a device such as an IP camera with a heater.
- Lower standby power – minimum standby power is 20mW, which is 10 times lower than the value for 802.3at, which is at 200mW. This can save a lot of energy, especially in PoE LED lighting.
- Autoclass – a minimum of 71W is delivered to the PD, but the PSE can automatically detect the actual max power drawn by the PD and adjust accordingly.
Additional Notes
Below are important factors to know:
- PD power – Make sure to refer to the power that is delivered to the PD, rather than the power that is output from the PSE. For example, if a camera needs 28W of power, it will not be sufficient to power the camera with 802.3at, which outputs 30W from the PSE, but only 25.5W is delivered to the PD.
- Voltage – for PSE devices that require a DC input to power up, be aware of the input voltage range of the different standards. For example, Type 4 requires a voltage range of 52 – 57VDC. 48VDC power supplies are very common, which means that the power supply needs to be able to be cranked up to 52V at a minimum to be able to power up an 802.3bt PD. Below is a table of the voltage ranges needed for each Type:
- Proprietary protocols – before 802.3bt was ratified by IEEE, there were devices that required more power than what 802.3at (30W) could provide. There were several proprietary protocols that were developed at that time to handle this issue. This was implemented mostly in the form of an injector. The basic mechanism of the operation was that the protocol would be negotiated to be 802.3at, but instead of delivering power over 2 pairs, it would deliver power over 4 pairs, allowing the power to be higher than 30W out of the PSE.
- Backward compatibility – all IEEE PoE standards/protocols are backward compatible. A device classified as an 802.3af PD will still work without any issue on an 802.3bt PSE.
Type 1 | Type 2 | Type 3 | Type 4 | |
PSE Voltage | 44-57VDC | 50-57VDC | 50-57VDC | 52-57VDC |
Managed PoE Switch Features
One of the most common Power Sourcing Equipment (PSE) types is the PoE switch, with managed PoE switches offering more advanced features compared to unmanaged switches. While an unmanaged PoE switch is essentially a plug-and-play device, a managed PoE switch provides the ability to configure both the network and the switch itself. A managed PoE switch from EtherWAN Systems, for example, offers additional configuration options specifically designed to optimize PoE functionality.
- PoE scheduling – Managed PoE switches enable advanced PoE scheduling, allowing users to configure individual PoE ports to provide power on specific days and times. This scheduling flexibility helps organizations optimize power usage and reduce energy consumption by powering devices only when needed.
- Proprietary mode – this allows high-power Powered Devices (PDs) to be powered by PoE ports at greater than 30W, while still being negotiated as 802.3at. This feature is ideal for devices that require higher power, ensuring efficient and reliable performance.
- PoE watchdog and recovery – The PoE watchdog and recovery feature allows individual PoE ports to be configured to ping connected PoE devices. If a device fails to respond within a specified time, the port will automatically reboot, effectively power cycling the device. This self-healing capability can recover devices without the need for manual intervention, significantly reducing downtime and minimizing maintenance costs, such as the need for truck rolls.
Conclusion
As PoE standards continue to expand, there will be new devices and applications to take advantage of the new technologies. PoE will steadily become more widespread than ever. EtherWAN’s range of hardened-grade PoE switches provide power to handle the latest 802.3bt standard, uninterrupted operation even in extreme temperatures (-40F to 167F ambient), and quality of life features such as proprietary mode and PoE watchdog. EtherWAN’s unmatched quality is backed by a limited lifetime warranty for hardened PoE switches.
Go here for more information: Hardened PoE Switches