Max: 15.4 W
Max: 30 W
Max: 60-100 W
How to Calculate PoE Power Budget
Calculating the Power over Ethernet (PoE) budget is a critical step in network planning. A "power budget" refers to the total amount of power a PoE switch can provide to all connected devices simultaneously. If the total power demand of your devices (IP cameras, VoIP phones, Access Points) exceeds the switch's budget, devices may reboot randomly or fail to power on.
Step-by-Step Guide
- Identify Device Class: Check the specification sheet of each device to find its PoE Class or maximum wattage (e.g., Class 2 is ~7W).
- Sum Total Wattage: Add up the maximum power consumption of all devices.
- Account for Cable Loss: Ethernet cables have resistance, which turns some power into heat. We recommend adding a 15% safety margin to your total calculation.
- Select the Right Switch: Choose a switch with a total PoE budget higher than your calculated requirement.
Common PoE Standards
- PoE (802.3af): Delivers up to 15.4W per port. Suitable for basic VoIP phones and static cameras.
- PoE+ (802.3at): Delivers up to 30W per port. Used for PTZ cameras, Wi-Fi 6 APs, and video phones.
- PoE++ (802.3bt): Delivers up to 60W (Type 3) or 100W (Type 4). Required for high-performance usage like digital signage or building automation.
Frequently Asked Questions
What happens if I exceed the PoE budget?
Most modern switches have a priority mechanism. They will cut power to low-priority ports (usually higher numbered ports) to keep high-priority devices running. This often manifests as cameras effectively "rebooting" at night when IR illuminators turn on and draw more power.
Why is cable loss important?
The standard allows for power loss over 100 meters of Cat5e/Cat6 cable. While the device gets what it needs, the switch must send more power to overcome resistance. A device needing 12W might require the switch to output 13-14W.
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