How LAN Cables Support Power over Ethernet (PoE) Devices

Power over Ethernet (PoE) technology has revolutionized the way devices are powered in various applications, including network infrastructure, security systems, and IoT devices. By leveraging LAN cables, PoE provides both data and power over a single Ethernet cable, eliminating the need for separate power cables. This article explores the inner workings of LAN cables and how they facilitate PoE.

Power Transmission over LAN Cables

LAN (Local Area Network) cables are typically used for data transmission. They consist of four pairs of twisted copper wires, each pair designed to transmit data signals. PoE cables, however, are specially designed to carry both data and power. They employ a specific wiring scheme that allows the unused pairs of wires to be dedicated to power transmission.

Types of PoE LAN Cables

There are different types of LAN cables that support PoE, each with its own maximum power output capability. The most common types include:

– Category 5e (Cat5e): Rated for a maximum power output of 15.4 watts (W).

– Category 6 (Cat6): Rated for a maximum power output of 30W.

– Category 6A (Cat6A): Rated for a maximum power output of 60W.

Power Injection Methods

There are two main methods of injecting power into PoE LAN cables:

– Active PoE: Uses an external power injector that inserts power into the Ethernet cable.

– Passive PoE: Draws power directly from the power supply unit (PSU) of the PoE-enabled device.

PoE Pin Configuration

The pin configuration of a PoE-enabled LAN cable is crucial for ensuring proper power transmission. The two pairs of wires used for power transmission are typically designated as “spare” pairs (pins 4 and 5, and pins 7 and 8). The power source (either the power injector or the PSU) applies a voltage (typically 48V) between these pairs.

Limitations of LAN Cables for PoE

While LAN cables provide a convenient solution for PoE, they have certain limitations:

– Distance: The maximum distance over which PoE can be transmitted effectively depends on the cable type and power requirements of the device.

– Cable Quality: The quality of the LAN cable can affect the efficiency of power transmission. Inferior cables may experience power loss or interference.

– Power Capacity: The power output capability of LAN cables is limited, which may restrict the types of devices that can be powered over Ethernet.