What is the difference between active and passive PoE?

Active PoE and Passive PoE are two methods of delivering power over Ethernet cables, but they differ significantly in terms of functionality, safety, and compatibility.

1. Active PoE

Active PoE adheres to official standards, such as IEEE 802.3af, 802.3at (PoE+), and 802.3bt (PoE++). It involves intelligent communication between the power source (PoE switch or injector) and the powered device (e.g., IP camera or access point) to determine if the device is PoE-compatible and how much power is needed.

Key Characteristics of Active PoE:

--- Standards-Based: Follows IEEE standards (802.3af/at/bt).

--- Power Negotiation: The PoE switch or injector communicates with the device to deliver the correct amount of power, preventing damage to non-PoE devices.

--- Voltage: Commonly 44-57V for IEEE 802.3af/at and up to 57V for IEEE 802.3bt.

--- Compatibility: Ensures safe operation with any IEEE-compliant PoE device, including backward compatibility with previous PoE versions.

--- Safety: Built-in detection mechanisms to avoid delivering power to non-PoE devices, reducing the risk of over-voltage damage.

Applications:

--- Commonly used in enterprise-grade networks where safety, reliability, and standard compliance are critical.

--- Powers devices like VoIP phones, IP cameras, wireless access points, and other networked devices.

2. Passive PoE

Passive PoE does not follow any specific standard and does not include any form of power negotiation. It sends a fixed voltage over the Ethernet cable, regardless of whether the connected device is PoE-capable or not.

Key Characteristics of Passive PoE:

--- No Power Negotiation: Delivers power without checking whether the device is PoE-compatible.

--- Fixed Voltage: Typically operates at a fixed voltage, usually 24V or 48V, depending on the system.

--- Compatibility Issues: Requires devices to be specifically designed to work with the fixed voltage. Connecting a non-PoE device or a device with incompatible power requirements may result in damage.

--- Less Safe: Since there is no detection mechanism, it is easier to damage non-PoE devices by accidentally supplying power to them.

Applications:

--- Often used in small or specialized networks, such as wireless ISP equipment or specific home networking setups, where cost is a factor, and power negotiation isn't needed.

--- Powers devices like some proprietary wireless access points, cameras, and outdoor networking gear that is designed for Passive PoE.

Key Differences:

Which One to Choose?

Active PoE is the better option for most scenarios, especially in enterprise networks, as it ensures compatibility, safety, and scalability.

Passive PoE is more cost-effective but should only be used with devices specifically designed for it. It’s more common in niche applications or smaller network setups where cost is a priority, and users are aware of the risks.

If you are unsure about the device’s compatibility, Active PoE is the safer choice.