How Much Power Does PoE Supply? A Comprehensive Guide

Power over Ethernet (PoE) technology has revolutionized the way network devices are powered and connected. By delivering both data and electrical power over a single Ethernet cable, PoE simplifies installation, reduces clutter, and enhances flexibility. But one of the most common questions users and IT professionals ask is: how much power does PoE supply? In this article, we will explore the power capabilities of PoE, break down the different standards, and explain what factors influence the power delivered to devices.

What is Power over Ethernet (PoE)?

PoE is a technology that enables Ethernet cables to carry electrical power in addition to data signals. This eliminates the need for separate power supplies or outlets for network devices such as IP cameras, wireless access points, VoIP phones, and other PoE-enabled equipment. The power supplied via PoE is standardized to ensure compatibility and safety.

PoE Standards and Their Power Specifications

PoE power delivery is governed by IEEE standards, which define the maximum power that can be supplied over Ethernet cables:

IEEE 802.3af (PoE): The original PoE standard, ratified in 2003, delivers up to 15.4 watts of DC power per port. After accounting for power loss in the cable, about 12.95 watts is available to the powered device (PD).

IEEE 802.3at (PoE+): An enhanced standard introduced in 2009, PoE+ can supply up to 30 watts per port, with about 25.5 watts available to the PD.

IEEE 802.3bt (PoE++ or 4PPoE): The latest standard, ratified in 2018, comes in two types:

Type 3: Provides up to 60 watts per port.

Type 4: Delivers up to 90-100 watts per port.

Factors Affecting PoE Power Delivery

Several factors influence how much power is actually delivered to a device over PoE:

Cable Length and Quality: Longer cables lead to higher power loss due to resistance. High-quality, thicker cables (Cat6 or above) reduce this loss.

Number of Active Pairs: PoE uses either two or four twisted pairs in the cable to deliver power. More pairs mean higher power capacity and less voltage drop.

Device Power Requirements: Devices must be compatible with the PoE standard and have defined power classes to negotiate the correct amount of power.

Power Classes and Device Negotiation

PoE devices and power sourcing equipment (PSE) use a classification system to determine how much power is needed:

Classes range from 0 to 4 (and beyond with newer standards), each indicating a specific power range.

During the initial handshake, the PSE detects the PD’s class and supplies the appropriate power to avoid overloading the device or the network.

Real-World Applications and Power Needs

Different devices require varying levels of power:

VoIP Phones: Typically need 3 to 7 watts.

Wireless Access Points: Usually require 7 to 15 watts depending on the model.

IP Cameras: Can range from 5 watts for basic models to over 30 watts for PTZ (pan-tilt-zoom) cameras with heaters or IR lighting.

Thin Clients and Mini PCs: Some advanced devices require up to 60 watts or more, making PoE++ ideal.

Benefits of Higher Power PoE Standards

The evolution from 802.3af to 802.3bt has enabled new possibilities:

Powering devices like LED lighting, digital signage, and even laptops.

Simplifying installations by reducing the need for additional electrical wiring.

Supporting more powerful network devices and enhancing network flexibility.

Limitations and Safety Considerations

While PoE is versatile, there are limits:

The maximum power per port is capped by the standard to avoid cable overheating.

Using non-compliant cables or devices can cause power delivery issues.

Proper installation and certification are essential to maintain safety and performance.

Understanding how much power PoE supplies is crucial for designing efficient and reliable network infrastructures. The power capabilities have significantly increased with evolving standards, from 15.4 watts in IEEE 802.3af to up to 100 watts in IEEE 802.3bt. Factors such as cable quality, length, and device power requirements influence the actual power delivered. With these advancements, PoE continues to expand its role beyond simple network devices to powering a wide range of equipment, making it an indispensable technology in modern networking.

By selecting the right PoE standard and ensuring proper installation, businesses can enjoy simplified setups, reduced costs, and enhanced scalability for their network-powered devices.