Power over Ethernet: How Much Power Can PoE Deliver?

Power over Ethernet can deliver anywhere from 15.4 watts to 90 watts per port, depending on the PoE standard being used. That range is one of the reasons PoE has expanded far beyond its early use with devices such as IP phones.

Higher-power PoE can now support wireless access points, cameras, building sensors, LED lighting, controls and other connected equipment.

There is an important distinction, however, between the maximum power a PoE source can provide and the amount of power that reaches the connected device.

What Is the Maximum Wattage for PoE?

The maximum power available depends on the PoE Type and IEEE standard.

The PSE, or Power Sourcing Equipment, is the equipment supplying power to the Ethernet connection. A PoE network switch is a common example. The receiving equipment is called the Powered Device (PD).

For a closer comparison of the standards themselves, see PoE vs. PoE+ vs. PoE++: What’s the Difference?

Why Does a 90W PoE Port Not Deliver 90W to the Device?

Some electrical power is lost as it travels through the Ethernet cable. This is why the IEEE specifications distinguish between power supplied by the PSE and power that must be available at the powered device.

For example, IEEE Type 4 PoE allows the PSE to provide up to 90 watts. The standard accounts for cable losses so that up to approximately 71 watts can be available at the powered device.

Cable length, conductor resistance, cable construction and operating conditions can all affect power loss.

This distinction is particularly important when designing systems with devices that have higher power requirements. The rating of the PoE port alone does not tell you how much usable power will necessarily be available at the other end of the cable.

Does a PoE Port Always Use Its Maximum Wattage?

No. A 90W PoE port does not continuously send 90 watts to every connected device.

Standards-based PoE equipment determines whether a compatible powered device is connected and establishes the appropriate power level. The connected device then draws the power it requires within the capabilities of the PoE connection.

A device requiring 20 watts, for example, does not suddenly consume 90 watts simply because it is connected to a 90W-capable port.

This allows devices with different power requirements to operate on the same PoE network when the equipment is properly designed and compatible.

How Much PoE Power Does a Device Need?

The required wattage depends on the device.

Small sensors and other low-power electronics may require only a few watts. Wireless access points, cameras and control devices can require more. Equipment such as LED lighting and motorized building devices may require considerably higher power.

The important number when selecting PoE equipment is the device’s maximum power requirement, not simply its typical operating consumption.

A system should be designed so that sufficient power is available when the device is operating at its maximum specified demand.

What Is 90W PoE Used For?

The introduction of IEEE 802.3bt significantly increased the amount of power that could be carried over standards-based Ethernet.

Type 4 PoE can supply as much as 90 watts at the PSE. That makes Ethernet practical for equipment that would have exceeded the limits of earlier PoE standards.

In intelligent buildings, higher-power PoE can be used to support devices such as LED lighting, automated controls and other connected building equipment.

We’ll cover 90W PoE and IEEE 802.3bt in greater detail in their own technical resources rather than expanding those subjects here.

What Is a PoE Power Budget?

Individual port capacity is only part of the equation.

A PoE switch may have multiple ports capable of supplying relatively high wattage while still having a limit on the total amount of PoE power available across the switch. This is known as the PoE power budget.

For example, the combined power demand of all connected devices must remain within the power capacity available from the switch or other power source.

This becomes increasingly important in larger deployments where dozens of devices may receive power from the same network infrastructure.

See How Do You Calculate a PoE Power Budget? for a dedicated explanation of sizing power across multiple PoE devices.

How Much PoE Power Is Available Over Longer Cable Runs?

Ethernet cable resistance causes some power loss between the PSE and the powered device. IEEE PoE standards account for this loss when defining how much power must be available to the device.

Distance is therefore an important consideration when planning a PoE system, particularly for higher-power equipment.

The standard Ethernet channel is generally limited to 100 meters, or 328 feet. Cable category, conductor size and installation conditions can also matter when delivering higher levels of power.

For the distance question specifically, see How Far Can Power over Ethernet Run?