What are the different PoE standards (IEEE 802.3af/at/bt)?

Power over Ethernet (PoE) standards define how power is delivered over Ethernet cables to power networked devices, such as IP cameras, VoIP phones, and wireless access points. The primary PoE standards are IEEE 802.3af, IEEE 802.3at, and IEEE 802.3bt. Each standard outlines the power levels, voltage, and maximum current that can be provided to devices. Here’s a breakdown of the different PoE standards:

1. IEEE 802.3af (PoE)

Introduced: 2003

Power Output per Port: Up to 15.4W at the switch

Available Power for Devices: Up to 12.95W (after accounting for power loss over the cable)

Voltage: 44-57V

Maximum Current: 350mA

Cable Type: Requires Cat5 or higher (Cat5e, Cat6, etc.)

Typical Devices Supported:

--- VoIP phones

--- Basic IP cameras (non-PTZ)

--- Low-power wireless access points

Overview: The IEEE 802.3af standard, commonly known as PoE, provides up to 15.4 watts of power per port. After considering power losses over the Ethernet cable, about 12.95W is available to power the device. This standard is sufficient for low-power devices such as VoIP phones and standard IP cameras but may not provide enough power for advanced devices with higher energy demands.

2. IEEE 802.3at (PoE+)

Introduced: 2009

Power Output per Port: Up to 30W at the switch

Available Power for Devices: Up to 25.5W

Voltage: 50-57V

Maximum Current: 600mA

Cable Type: Requires Cat5 or higher

Typical Devices Supported:

--- Wireless access points with multiple antennas

--- PTZ (Pan-Tilt-Zoom) IP cameras

--- Advanced IP phones with video

--- LED lighting

Overview: IEEE 802.3at, known as PoE+, significantly increased the power delivery capabilities over PoE, providing up to 30W per port, with 25.5W available for devices. This higher power budget makes PoE+ suitable for more demanding devices, such as advanced IP cameras (PTZ cameras), wireless access points, and devices that support video functionality.

3. IEEE 802.3bt (PoE++ or 4-Pair PoE)

Introduced: 2018

Power Output per Port (Type 3): Up to 60W at the switch

Available Power for Devices (Type 3): Up to 51W

Power Output per Port (Type 4): Up to 100W at the switch

Available Power for Devices (Type 4): Up to 71.3W

Voltage (Type 3): 50-57V

Voltage (Type 4): 52-57V

Maximum Current (Type 3): 600mA per pair

Maximum Current (Type 4): 960mA per pair

Cable Type: Requires Cat5e or higher for Type 3 and Cat6 or higher for Type 4 (for optimal performance)

Typical Devices Supported:

--- High-end wireless access points (Wi-Fi 6/6E)

--- High-power PTZ cameras

--- Digital signage

--- Building automation systems (e.g., smart lighting, HVAC controls)

--- Thin client workstations

--- POS (Point of Sale) systems

Overview: IEEE 802.3bt, also known as PoE++ or 4-Pair PoE, further expands the power capacity by using all four pairs of wires in an Ethernet cable to deliver power. This standard has two power levels: Type 3 (up to 60W) and Type 4 (up to 100W). PoE++ is designed to support high-power devices like large digital displays, high-performance wireless access points, and even IoT devices in smart buildings.

Summary of PoE Standards

Choosing the Right PoE Standard for Your Network

--- IEEE 802.3af (PoE): Ideal for networks with low-power devices such as VoIP phones, basic IP cameras, and simple access points.

--- IEEE 802.3at (PoE+): Best suited for medium-power devices like PTZ cameras, advanced access points, and devices requiring more than 15.4W.

--- IEEE 802.3bt (PoE++): Necessary for high-power devices such as Wi-Fi 6 access points, building automation systems, large LED lighting arrays, and other power-hungry equipment.

Make sure to assess the power needs of your connected devices and choose a PoE switch or injector that supports the appropriate standard. For future-proofing, opting for PoE+ or PoE++ switches ensures your network can handle more demanding devices as your infrastructure grows.