Understanding PoE Standards and Wattage

Updated on Mar 24, 2022 by

PoE (Power over Ethernet) technology allows PSE (Power Sourcing Equipment, such as a PoE switch) to use Ethernet cables to deliver both power and data simultaneously to PD (Powered Device, like IP cameras and VoIP phones), which can simplify cabling installation and save cost. Different PoE standards like IEEE802.3af,802.3at, and 802.3bt are released by IEEE (Institute of Electrical and Electronic Engineers) to regulate the amount of power delivered to those PDs. Then how much do you know about those PoE standards and PoE wattage? How many PDs can be connected to a PSE based on different PoE wattages? Here it offers a detailed explanation.

PoE Standards Introduction

PoE standards come in three types: IEEE 802.3af, IEEE 802.3at, and IEEE 802.3bt. These standards define the minimum power that Power Sourcing Equipment (PSE) can deliver and the maximum power that Powered Devices (PD) will expect to receive.

PoE Standards and PoE Wattage

Figure 1: IEEE 802.3af, IEEE 802.3at and IEEE 802.3bt Introduction

1. IEEE 802.3af (Standard PoE)

Operating within a voltage range of 44-57V and delivering a current of 10-350mA, IEEE 802.3af provides a maximum power output of 15.4W per port. Due to Ethernet cable power loss, the minimum guaranteed power available at the PD is 12.95W per port. This standard supports devices like VoIP phones and sensors.

2. IEEE 802.3at (PoE+)

As an updated standard, PoE+ is backward-compatible with IEEE 802.3af. It operates with a supply voltage ranging from 50V to 57V and a supply current of 10-600mA. PoE+ delivers up to 30W of power on each PSE port, ensuring a minimum power output of 25W per port. This standard is suitable for devices like wireless access points and video conferencing systems.

3. IEEE 802.3bt

IEEE 802.3bt is the latest PoE standard that defines two types of powering/wattage standards - Type 3 and Type 4. They will increase the maximum PoE power by delivering more power through two or more pairs of Ethernet cables. In Type 3 and Type 4 modes, PSEs will identify the PDs and allocate power based on the maximum power requirement of the PDs, resulting in an enhanced power delivery system. The standard will include support for 2.5GBASE-T, 5GBASE-T, and 10GBASE-T while existing standards have a maximum speed of 1-Gbps. It's designed for demanding applications such as laptops and LED lighting.

a. Type 3 (PoE++)

Type 3, also known as PoE++, can provide up to 60W per PoE port (ensuring a minimum of 51W on each PD port). It's suitable for powering devices such as video conferencing systems components.

b. Type 4 (Higher-Power PoE)

Type 4 offers a maximum power output of 100W per PoE port (with a minimum of 71W on each PD port). This level of power delivery is ideal for devices like laptops and TVs.

Both the two modes of IEEE 802.3bt are backward compatible with 802.3af and 802.3at. The following table concludes the specifications of the PoE standards, including PoE wattage.

Name IEEE  Standard PD Min. Power Per Port PSE Max. Power Per Port Cable Category Power Over Pairs Released Time
PoE IEEE 802.3af 12.95W 15.4W Cat5e 2 pairs 2003
PoE+ IEEE 802.3at 25W 30W Cat5e 2 pairs 2009
PoE++ IEEE 802.3bt 51W 60W Cat5e 2 pairs class0-4, 4 pairs class5-6 2018
PoE++ IEEE 802.3bt 71W 100W Cat5e 4 pairs class7-8 2018

Understanding PoE Wattage

As mentioned above, IEEE 802.3af delivers a maximum of 15.4W per port, while PoE+ supports up to 30W. The challenge arises when planning to connect multiple devices to a single PoE/PoE+ switch. It's essential to ensure that the total power requirements of these devices do not exceed the switch's maximum power wattage.

For example, let's take the FS S3400-24T4FP, a managed PoE+ switch with 24 RJ45 ports and 4 SFP ports. Compliant with IEEE 802.3af/at standards, this switch has a total power budget of 370W. This means it can concurrently power 24 devices compliant with PoE standards (15.4W x 24 = 369.6, which is less than 370W). It can also support 12 devices compliant with PoE+ standards (30W x 12 = 360W, which is again less than 370W).

Figure 2: Applications of FS PoE+ switches.

But there's no need to worry, modern network switches are intelligent. When a device is connected, they automatically detect whether it's compatible with PoE or PoE+. If it's a PoE-enabled device requiring 5W, the switch supplies precisely that. If the device demands 20W, the switch steps up. But if you connect a device without PoE capability, rest assured, the switch will deliver data only.

How Much PoE Wattages are Need?

The power needs of your devices depend on what you're connecting. Most devices, such as security cameras, IP phones and standard wireless APs, require no more than 30 watts.

However, some devices, like 802.11ac wireless APs with multiple USB ports and radios, need over 30 watts for peak performance. For these cases, PoE++ or PoH switches are the solution. Keep in mind that some devices can adapt to lower power availability by using fewer radios or disabling features.

FS Network Switches: Your PoE Solution

FS now offers PoE/PoE+/PoE++ switches that adhere to the PoE standards, providing enhanced security and improved capabilities. They are available in 8/16/24/48 port options. These switches support layer 2+ switching features like VLAN. They also offer advanced management like WEB, CLI, TELNET, and SNMP. FS PoE/PoE+ switches can power any 802.3af or 802.3at device on the market, offering flexibility and security. The following table lists the specifications of 4 FS PoE/PoE+/PoE++ switches.

Model PoE Standard  Port Switch Capacity Power Budget Forwarding Rate Fans AC/DC Power Supply


IEEE 802.3af/at 8x RJ45 | 2x SFP 20 Gbps 240W 15 Mpps With Fans AC


IEEE 802.3af/at 24x RJ45 | 2x SFP+, 2x RJ45/SFP 128 Gbps 740W 96 Mpps With Fans AC/DC


IEEE 802.3af/at/bt 24x Base-T | 4x SFP+, 4x SFP28 760 Gbps 740W 565 Mpps With Fans AC


Understanding PoE standards and wattage is crucial for efficient device connections. By matching your device's power requirements with the right PoE standard, you ensure seamless operation. PoE technology simplifies complex cabling and provides flexibility in power delivery.


Related Article: Demystifying PoE Network: Features, Standards, Types, and Common FAQs

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