Power over Ethernet, PoE technology transmits data and power simultaneously over a single Ethernet cable, simplifying network deployment and reducing costs.
Different devices need different amounts of power. So, it is important to pick a PoE injector that meets IEEE standards. (IEEE 802.3af/at/bt Guide: Choosing Compliant PoE Injectors)
This article will look at the main differences between the three key standards: IEEE 802.3af, 802.3at, and 802.3bt. It will also offer a guide to help you choose.
1. Analysis of IEEE 802.3af/at/bt standards
IEEE 802.3af (PoE)
Power and voltage: PSE output power is 15.4W, and the actual available power of the powered device is 12.95W. At this time, the voltage range is 44-57V, and the typical value is 48V.
Application scenarios: Suitable for low-power devices. Such as IP phones, basic surveillance cameras, and low-power wireless access points.
Power supply mode: Power is transmitted through two pairs of wires, compatible with Cat5 and above cables.
IEEE 802.3at (PoE+)
Power and voltage: PSE output power is 30W, PD can use 25.5W; voltage range is 50-57V.
Application scenarios: Support higher power devices, such as PTZ cameras, dual-band wireless APs, and digital signage.
Upgrade features: We are adding Class 4 classification. This will improve the current carrying capacity. It will also require using high-quality Cat5e or Cat6 cables.
IEEE 802.3bt (PoE++)
Power and voltage: Divided into Type 3 (60W PSE/51W PD) and Type 4 (90W PSE/71.3W PD), with a voltage range of 52-57V.
Application scenarios: Suitable for high-power devices, such as LED lighting systems, industrial IoT terminals, high-performance APs, and 4K monitoring equipment.
Power supply method: Four pairs of wires are used to transmit power, and Cat6a and above cables are required. Automatic classification and single/dual-feature PD topology are also supported.
2. Key factors for selecting a PoE power supply that meets the standard
Power demand matching
Choose the right standard based on the device's power: For example, CETUS's power supply supports the IEEE 802.3bt standard. It can provide up to 90W output for high-power devices.
Compatibility and classification mechanism
Detection and classification: The power supply must support PD detection and classification to ensure dynamic power allocation and avoid overload28.
Backward compatibility: High-standard power supplies should be compatible with low-power devices to achieve flexible deployment.
Cable and heat dissipation requirements
Cable specifications: 802.3bt needs four pairs of wires for power. Cat6a is recommended to lower resistance loss. 802.3af/at can use Cat5e, but you should think about voltage drop over long distances.
Heat dissipation design: High-power power supplies must improve the heat dissipation structure. This helps keep the cable bundle's temperature rise below 10℃, which is the limit recommended by IEEE.
Safety and management functions
Safety protection is important. Overcurrent and short-circuit protection help keep equipment and people safe. Electrical isolation is also essential for safety.
Remote management: Support remote monitoring, power cycling and real-time load adjustment to improve operation and maintenance efficiency67.
3. Application scenarios
Small and medium power scenarios (<30W)
Recommended standard: 802.3af/at: For example, when using IP phones or simple monitoring systems, CETUS's 802.3at power supply can meet the needs. It also leaves room for future expansion.
High power and complex environment
Recommended standard: 802.3bt: This is good for LED lights, industrial sensors, or data center equipment in smart buildings. It needs a four-pair power supply and a design that helps with heat dissipation.
Hybrid device deployment
Strategy: Choose a power supply that supports multiple standards. Such as models compatible with 802.3af/at/bt, to meet the power requirements of different devices.
4. Future trends
As IoT and AI technologies become more popular, PoE will grow in power and intelligence. The IEEE 802.3bt standard has paved the way for 90W power supply, and may support higher power levels in the future. When selecting a power supply, pay attention to the following trends:
Energy efficiency optimization: Combine Energy-Efficient Ethernet (EEE) to reduce standby power consumption.
Security enhancement: Integrated encryption protocol prevents malicious interference in the power supply link.
The selection of PoE power supply requires comprehensive consideration of power, compatibility, cable and management functions. We can create a reliable power supply network. This is done by matching device needs with standard features. One example is CETUS's support for multiple protocols.
