What’s PoE

Q&A of functional explanation or specification parameters
Updated 10-25-2022 06:53:05 AM 21552

Here are some questions about PoE (Power Over Ethernet).

Q1: What is PoE?

Power over Ethernet (PoE) is a technology that allows network switches to transmit both power and data through an Ethernet cable simultaneously. It has two types: Active(Standard) PoE and Passive PoE.

Q2: What is the difference between Active(Standard) PoE and Passive PoE?

Active PoE: Also known as standard PoE, refers to any type of PoE in which the appropriate voltage is negotiated between Power Sourcing Equipment (PSE) and Powered Device(PD). Active PoE switches are standard PoE-compatible devices, so they are also called standard PoE switches. Before powering up, active PoE switches will check to ensure the electrical power is compatible between the switch and the powered device. If it isn’t, the active PoE switch will not supply power to the device, avoiding damage to the device.

Passive PoE: A non-standard form of PoE. It can also be used to power over the Ethernet cable, but no negotiation or communication process is required. Passive PoE doesn’t conform to any IEEE standards. When using a passive PoE switch/adapter in a network, the power supply is "always on", which means that regardless of whether the end device supports PoE or not, it always sends current through the Ethernet cable at a certain voltage. Therefore, using a passive PoE switch/adapter that exceeds the voltage supported by the end device may burn the end device.

Q3: What are the standards of Active PoE?

  1. IEEE802.3af standard

IEEE802.3af standard defines the maximum output power from a single port to be 15.4W, and it can supply power to devices under 12.95W (such as IP cameras) through an Ethernet cable.

  1. IEEE802.3at standard

IEEE802.3at standard is based on IEEE802.3af and can be regarded as the enhanced version of the IEEE802.3af. The power from a single port is up to 30W, and it can supply power to devices under 25W, which can meet the requirement of higher-power devices such as video Phones, PTZ devices and etc.

  1. IEEE802.3bt standard

802.3bt is one of the newest standards and can provide up to 60W from a single port, and it can supply power to devices under 51W. It is usually used to power a device that requires high power.

IEEE PoE standards have backward compatibility. The latest standard, IEEE 802.3bt, is fully backward compatible with the older IEEE 802.3af and IEEE 802.3at standards.

Q4: Does Passive PoE have any standards?

Passive PoE does not adhere to any IEEE standard. Passive PoE switches/adapters are mainly divided into 12V, 24V, and 48V according to the output voltage provided. When purchasing a passive PoE switch/adapter, you need to consider its voltage according to the voltage of the powered device. Connecting the wrong voltage may cause permanent electrical damage to the powered device.

Q5: What PoE products does TP-Link have?

PoE switch

Omada EAP

Deco PoE

Where can I learn more about the PoE standard?

Please refer to it here.

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