What is PoE Budget and How Much Do I Really Need?

When using a Switch or Power Sourcing Equipment (PSE), the PSE needs to meet the power requirements of Powered Devices (PDs). Examples of PDs include IP surveillance cameras, Voice over IP (VoIP), and Wireless Access Points (WAPs).

All PSEs have a PoE Budget - This is the total amount of power PSEs can supply to PDs at one time, measured in watts.
In this article, we will explain why the budget is often over-estimated.

Various Types of PoE

Listed below are the different types of PoE:

• 802.3af – Intelligent PoE providing a maximum of 15.4W of power per port
• 802.3at – Intelligent PoE providing a maximum of 30W of power per port
• 802.3bt – Intelligent PoE providing a maximum of 60W of power per port
• Passive PoE – Power budget is determined by the Power Supply

If your PD supports 802.3af PoE, this doesn't automatically mean that it requires the full 15.4W. Every product should display the Maximum Power Consumption on its datasheet. This is the maximum power that the device could draw, not necessarily the power it will require, even when functioning at full capacity.

Max Power Consumption

When referring to PoE budget, you're only referring to the required power of the connected devices (PDs) and not the power needed for the PSE to function.

It is standard practice to use the maximum power consumption to assist with the calculation of your required PoE budget, however, this often causes an over-spec on the required PoE budget. The maximum power consumption supplied by manufacturers is the power consumption of the unit at maximum capacity, and in reality, will likely never be achieved.

The below shows a UAP-AC-LR set to high output power, servicing 4 clients. As you can see, the power consumption is only half of the anticipated maximum consumption. Even if we were to serve an additional 40 simultaneous client connections, it is unlikely we would reach the 6.5W reported on the datasheet.



Maximum Power Consumption as indicated on datasheets is a fail-safe. It provides an indication reference for budgeting purposes. It's always a good idea to make provision for potential growth, however, it's not necessary to waste money on purchasing switches with massive PoE budgets.

In reality, very few products actually need over 8W. There are exceptions with things like PTZ cameras or high-power access points that go above and beyond 8W, but these are not a common occurrence.

The below example shows a US24-250 UniFi Switch, fully-populated, running 19 cameras (a mixture of UVC-G3DOME & UVC-G3B) as well as 4x UniFi Access Points (3x UAP-AC-LR & 1x UAP-AC-NHD).

According to the Max Power Consumption listed on these products' datasheets, we would require a PoE budget of 106W. As shown below, the total consumption is only 61.96W.



Maximum consumption figures are provided to assist you when calculating your PoE budget but should not be the only factor considered. The number of concurrent clients, bandwidth requirements and usage times all factor into the maximum consumption at any one time.

Ubiquiti's range of USW UniFi Switches provides a comprehensive solution with slightly lower PoE budgets, a variety of ports including 802.3af/at/bt as well as SFP and SFP+ uplink options. 

If you need any assistance in planing your PoE budget or deciding on a PoE switch for your installation, feel free to contact one of our three branches for assistance.