PoE switch pins

PoE delivers power over specific RJ45 pins: Mode A uses pins 1, 2, 3, and 6, while Mode B uses pins 4, 5, 7, and 8.

Overview of PoE Pinouts

Power over Ethernet (PoE) allows devices such as IP cameras, VoIP phones, and wireless access points to receive both data and electrical power over a single Ethernet cable. PoE operates under IEEE standards 802.3af (PoE), 802.3at (PoE+), and 802.3bt (PoE++), with voltage typically ranging from 44–57V DC depending on the standard .

RJ45 Pin Usage

An RJ45 connector has 8 pins corresponding to 4 twisted pairs of wires. PoE can deliver power in two main modes:

• Mode A (Alternative A): Power is transmitted over the same pairs used for data. Specifically, pins 1 and 2 carry positive voltage, and pins 3 and 6 carry negative voltage. This mode is most common in modern PoE devices .
• Mode B (Alternative B): Power is transmitted over the spare pairs not used for data. Pins 4 and 5 carry positive voltage, and pins 7 and 8 carry negative voltage. This mode is less common and may be found in legacy systems .

Cable and Standard Considerations

• Cable type: Cat5e, Cat6, or higher is recommended for PoE, especially for higher power levels. Cat3 can be used for lower power applications .
• Power levels:
  • IEEE 802.3af (PoE) – up to 15.4W
  • IEEE 802.3at (PoE+) – up to 30W
  • IEEE 802.3bt (PoE++/4PPoE) – up to 60–90W using all four pairs .

Practical Tips

• Ensure the PoE switch and powered device (PD) use the same mode (A or B) to avoid power delivery issues.
• Use Cat5e or higher cables for reliable power transmission, especially for longer runs or high-power devices.
• For higher power PoE++ devices, all four pairs may be used to deliver power, increasing efficiency and supporting more demanding equipment . Understanding the PoE pinout ensures proper wiring, safe power delivery, and compatibility between switches and devices.