Planning tool
PoE budget calculator
A switch has a total PoE budget as well as a port count. This checks you will not run out of power before you run out of ports.
Result
Connected load
502W
Load with cable and surge allowance
552W
+10% for cable loss and start-up
PoE budget to buy
663W
Includes 20% headroom, split over all switches
PoE ports
50
3 switch(es) of 24 ports
Port standard needed
802.3at
Up to 30 W per port from the switch
- Problem:Over budget: the devices need 552 W and the switch gives 370 W. Some devices would not power up.
- Check:50 devices need 3 switches of 24 ports. Split the budget across them: the total above is shared, not per switch.
| Device | Qty | Each | Total |
|---|---|---|---|
| Fixed cameras | 16 | 10 W | 160 W |
| PTZ cameras (IR, heater) | 2 | 25 W | 50 W |
| Wi-Fi access points | 8 | 20 W | 160 W |
| IP phones | 20 | 5 W | 100 W |
| Door controllers and readers | 4 | 8 W | 32 W |
Method
How the numbers are worked out
Total, not per port
Each switch has a total PoE power budget shared by its ports. A 24-port switch with a 190 W budget cannot run 24 cameras at 10 W each, however many ports it has.
Allowance and headroom
The load is raised by an allowance for cable loss and start-up surges, then by headroom, so cameras with infrared and heaters can peak together.
Which PoE standard
The most demanding device sets the port type: 802.3af gives up to 12.95 W at the device, 802.3at 25.5 W, and 802.3bt up to 51 W (Type 3) or 71.3 W (Type 4).
Assumptions and limits
- Power at the device is lower than at the switch port because of cable loss; the allowance covers this for runs up to 100 m.
- Typical device figures are starting points. Use the data sheet of the model you will buy.
- Cameras with IR, heaters or PTZ motors draw most in cold, dark conditions.
Related
Nothing you type here leaves your device unless you choose to send it to us. These are planning estimates; a survey or the equipment data sheet confirms the final figures.
Want an engineer to check it?
Send us what you worked out and we will come back with a design based on the real site.