Understand these 7 PoE issues and you will thoroughly understand Power over Ethernet

In today's "Internet of Everything" era, smart buildings, security surveillance, wireless networks, and IoT applications are ubiquitous. You'll find one thing in common: these devices require not only data but also power. Power over Ethernet (PoE) is a two-in-one solution that meets these two critical needs.

Many people still have misunderstandings about PoE: Is it unstable? Is the power too low? Is it uneconomical? Should I replace all my equipment with the new standard?

In this article, we'll thoroughly explain PoE by answering seven frequently asked questions, helping you fully understand this critical technology that has become deeply integrated into enterprise networks.

First, is PoE reliable?

Many people's initial impression of PoE is that it's "unreliable," wondering if power transmitted through network cables can be reliable.

In fact, PoE's reliability rivals traditional power supply methods.

There are three reasons for this:

1. The maturity of Ethernet technology. PoE is built on Ethernet, one of the world's most mature transmission technologies, with decades of proven stability.

2. Intelligent power control. Before powering a PD (powered device, such as a camera or access point), a Power Sourcing Equipment (PSE) (such as a PoE switch) performs a handshake to confirm whether the device supports PoE and its required power. Only after confirmation will power be supplied, significantly reducing risk.

3. Power redundancy and centralized management. If a PoE switch is connected to a UPS, power outage protection can be achieved. Compared to traditional AC-powered single-point power supplies, centralized PoE power supply with a UPS is actually more stable.

So, PoE isn't "unreliable"; on the contrary, it's a safer and smarter power supply method.

Second, is PoE cost-effective?

Many companies ask, "Is PoE more expensive than separate power supply?" when working on projects—the answer is often that it saves money overall.

• Reduced cabling and labor costs
No need to run separate power cables for each device; a single network cable handles both data and power. For many projects, cabling costs can even be cut in half.

• Simple installation and maintenance
PoE switches offer centralized management and support remote restart of PDs. For example, if a camera crashes, an engineer can restore it with a single click in the equipment room, eliminating the need to climb stairs.

• Energy saving and scheduling
Some high-end PoE switches support timed power on and off, for example, shutting down some APs at night to save on electricity.

• Improved reliability through integration with a UPS
Traditional power supplies require each outlet to be connected to a separate UPS, while PoE only requires a UPS connection on the switch itself, resulting in lower costs.

So, from a CAPEX (capacity expenditure) + OPEX (operation and maintenance expenditure) perspective, PoE is cost-effective.

Third, is PoE power limited?
This is probably the most common misconception. Many people believe that PoE can only power low-power devices, such as phones.

The truth is: PoE power standards are constantly evolving:

• IEEE 802.3af (PoE): Maximum power of 15.4W, commonly used for VoIP phones and wireless access points.
• IEEE 802.3at (PoE+): Maximum power of 30W, suitable for PTZ cameras and dual-band Wi-Fi access points.
• IEEE 802.3bt (PoE++): Maximum power of 90W, capable of driving large-screen displays, conference tablets, and even some small industrial control equipment.

At the same time, with the advancement of semiconductor energy-saving technology, many devices are consuming increasingly lower power. For example, early WiFi 5 APs may have required 20W, while now WiFi 6 APs often require only 15W, achieving even greater efficiency.

Thus, PoE isn't just about "low power," but rather its power consumption is constantly increasing, extending its scope of application.

Fourth, is PoE suitable for the building sector?

Some people wonder, "Will using PoE be a hassle with so many devices in a building?" The answer is that PoE is highly suitable for building deployments and has even become a "standard" feature in smart buildings.

• Surveillance systems: IP cameras are often installed in locations with inconvenient power supply, and PoE is a perfect solution.

• Wireless networks: APs offer flexible deployment locations, unrestricted by outlets.

• Smart lighting: Many LED lamps now support PoE, enabling both dimming and energy savings.

• Access control and security: Access controllers, sensors, and more can all be powered by PoE.

A typical example: Some "smart buildings" even use PoE to power the entire floor's lighting system, which is then centrally controlled by a switch, reducing energy consumption by over 30% compared to traditional lighting systems.

Fifth, is PoE suitable for the Internet of Things?

With the explosion of the Internet of Things (IoT), millions of sensors and endpoints need to be connected to the network. Many people assume that these small devices rely on batteries, but PoE actually offers significant advantages in the IoT:

1. Eliminate battery replacements
If large-scale sensors rely on batteries, maintenance costs are extremely high. PoE allows sensors to be always online, eliminating the need for frequent battery replacements.

2. Improved security
Wireless connections are susceptible to interference and attacks, while PoE provides a wired connection that is stable and difficult to hack.

3. Support for edge computing
IoT gateways typically consume a lot of power, which PoE+ or PoE++ can fully meet.

4. Typical applications
• Smart parking sensors
• Industrial IoT monitoring
• Smart home gateways
It can be said that PoE is the "hidden hero" in the implementation of the IoT.

Sixth, will PoE consume a lot of power?
Many engineers worry about PoE's "high losses." In fact, energy efficiency was considered when the IEEE standard was developed:

• Power Cable Pairs
PoE initially used two twisted-pair cables, but the PoE++ standard now uses four pairs, reducing resistance and losses.

• Cable Specifications
Category 5 or higher is required, with a maximum transmission distance of 100 meters. Within this range, loss control is perfectly acceptable.

• Upper Resistance Limit
The standard stipulates that the DC loop resistance must not exceed 12.5Ω to ensure power efficiency.

In other words, as long as qualified network cables are used and the wiring is done properly, PoE power loss is not a problem at all.

Seventh, Do I need to replace my equipment with the new standard?
A final common misconception is: With the release of PoE++ (IEEE 802.3bt), does that mean I need to replace all my old equipment?

In fact, there's no need to worry. The PoE standard is backward-compatible:

• PoE++ switches can power both PoE and PoE+ devices;
• Devices that don't support PoE won't be "hard-powered" because the PSE will first confirm the handshake;
• Devices with different standards can coexist on the network.

Therefore, when enterprises upgrade their PoE switches, they don't need to completely rebuild; instead, they can proceed gradually and with compatibility.