How do I calculate the power requirements for a 24-port PoE switch?

Calculating the power requirements for a 24-port PoE (Power over Ethernet) switch involves assessing the total power budget based on the PoE standard, the number of active ports, and any additional power demands of the switch itself. Here's a step-by-step guide:

1. Understand the PoE Standards

Different PoE standards provide varying power levels per port. Here are the common standards:

The "Power Drawn from Switch" includes some overhead due to inefficiency in power delivery.

2. Determine Device Power Requirements

Each connected device (e.g., IP cameras, VoIP phones, wireless access points) has specific power needs. Check the power requirements of all connected devices and match them with the PoE standard.

--- For example, if you are powering 12 IP cameras that require 15.4W each and 12 VoIP phones that need 7W each, your device power requirements will be:

（12×15.4W）+（12×7W）= 184.8W+84W = 268.8W

3. Factor in the Maximum Simultaneous Power

Not all ports might be used simultaneously, but if they are, you need to calculate for maximum usage.

For a fully utilized switch:

Total Power Required = Power per Port (PSE) × Number × Number of Ports

For example, if all 24 ports deliver 15.4W (PoE):

24 × 15.4W = 369.6W

4. Include the Switch's Own Power Consumption

The switch itself consumes some power for its internal operations (non-PoE functions). This is typically mentioned in the switch's specifications. For example, if the switch requires 50W to operate:

Total Power Requirement = PoE Power Requirement + Switch Power Consumption

For the example above:

369.6W + 50W = 419.6W

5. Check the Switch's Power Budget

PoE switches have a defined power budget (e.g., 400W, 500W, 600W). Make sure your calculated power requirement doesn't exceed the switch's budget. If it does, you might:

--- Use fewer active PoE ports.

--- Opt for a switch with a higher power budget.

--- Deploy a midspan injector for additional power delivery.

6. Consider Efficiency and Headroom

It's good practice to leave a 10–20% margin to account for efficiency losses and unexpected power spikes. For example:

Recommended Power Supply Rating = Total Power Requirement × 1.2

For a 419.6W requirement:

419.6W × 1.2 = 503.5W

Example Summary

If you are powering 24 devices (12 requiring 15.4W and 12 requiring 7W), plus a switch consuming 50W:

--- PoE Power Requirement: 268.8W

--- Switch Power Consumption: 50W

--- Total: 318.8W

--- Add 20% margin: 318.8W × 1.2 = 382.56W

Choose a power supply or PoE switch with a power budget of 400W or more.

Conclusion

To calculate the power requirements for a 24 port PoE switch:

1. Determine the PoE standard and power per port.

2. Sum the power requirements for all connected devices.

3. Add the switch's own power consumption.

4. Ensure the total power requirement is within the switch's budget.

5. Add a safety margin to account for efficiency and unexpected load.