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PoE switch to Ethernet cable transmission

Fiber and communications infrastructure knowledge brief Published 06 Dec 2024

Prepared for preliminary research by the ROGER FIBRE knowledge desk. Confirm optical interfaces, port or core capacity, electrical input and output, enclosure protection, thermal design and installation limits against current standards and product documentation.

A PoE switch transmits both electrical power and data over a single Ethernet cable, allowing devices like IP cameras and access points to operate without separate power sources.

How Po

E Works

Power over Ethernet (PoE) allows a switch, known as a Power Sourcing Equipment (PSE), to deliver DC power along with Ethernet data to a Powered Device (PD), such as an IP camera, VoIP phone, or Wi-Fi access point, using standard twisted-pair Ethernet cables like Cat5e or Cat6. The switch detects whether the connected device is PoE-compatible and negotiates the appropriate power level according to the standard (802. 3af, 802.

3at, or 802. 3bt),.

Cable and Pin Configuration

Ethernet cables typically have four twisted pairs of copper wires.

Po

E can transmit power using different methods: Alternative A (Mode A): Power is sent over the same pairs used for data (pins 1, 2, 3, and 6 for 10/100 Mbps Ethernet),. Alternative B (Mode B): Power is sent over the spare pairs (pins 4, 5, 7, and 8), separating power and data for easier troubleshooting. 4PPoE (4-pair mode): Uses all four pairs to deliver higher power levels, suitable for PoE++ devices.

For standard RJ45 connectors, pins 1, 2, 3, and 6 carry data, while pins 4, 5, 7, and 8 are used for power in Mode B. Gigabit Ethernet uses all four pairs for data, so power is overlaid on the same wires using a technique similar to phantom power, which does not interfere with data transmission.

Po

E Standards and Power Levels802. 3af (PoE): Up to 15. 4 W from the switch, 12.

95 W at the device. 802. 3at (PoE+): Up to 30 W from the switch, 25.

5 W at the device. 802. 3bt (PoE++): Up to 60 W or 90 W, supporting high-power devices like 4K cameras or LED lighting.

The switch automatically detects the PD and supplies the correct voltage and current, ensuring safe operation and preventing damage to non-PoE devices.

Benefits of Po

E Transmission

Simplified installation: Only one cable is needed for both power and data. Flexible device placement: Devices can be installed up to 100 meters from the switch without separate power outlets. Cost efficiency: Reduces the need for electrical wiring and outlets, lowering infrastructure costs.

Scalability: Additional PoE devices can be added easily without modifying existing power infrastructure. In summary, a PoE switch efficiently combines data and power transmission over Ethernet cables, using specific pin configurations and standards to safely power networked devices while maintaining high-speed data communication.

PoE switch to Ethernet cable transmission - ROGER FIBRE ATELIER [PDF]

PoE switch to Ethernet cable transmission

What is Power over Ethernet (PoE)?

Power over Ethernet (PoE) is a technique for delivering DC power to devices over copper Ethernet cabling, eliminating the need for separate power supplies and

Power over Ethernet

OverviewStandard implementationTechniquesStandards developmentUsesTerminologyPower management features and integrationNon-standard implementations

Standards-based Power over Ethernet is implemented following the specifications in IEEE 802.3af-2003 (which was later incorporated as Clause 33 into IEEE 802.3-2005) or the 2009 update, IEEE 802.3at. The standards require Category 5 cable or better for high power levels but allow using Category 3 cable if less power is required. In multi-pair cases, PoE supplies power as a common-mode signal over two or more of the differential pairs

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Technical note

This reference is intended for preliminary fiber and communications infrastructure research. Optical interface, fiber type, port or core capacity, electrical input and output, enclosure protection, cooling, installation limits and applicable standards must be verified for the specific project.

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