PoE Budget Calculator
Size switch wattage, port usage, and cable margin for cameras, access points, phones, and other powered endpoints.
Full Breakdown
| Standard | PD Max | PSE Max | Typical Use |
|---|---|---|---|
| 802.3af | 12.95 W | 15.4 W | Cams |
| 802.3at | 25.5 W | 30 W | APs |
| 802.3bt Type 3 | 51 W | 60 W | PTZ |
| 802.3bt Type 4 | 71.3 W | 90 W | Mini PCs |
| Cable | Ohm/100m | Max Run | Note |
|---|---|---|---|
| Cat5e 24AWG | 8.2 | 100m | Budget safe |
| Cat6 23AWG | 6.5 | 100m | Best balance |
| Cat6A 23AWG | 5.5 | 100m | Lower drop |
| CCA Cat5e | 13.5 | 60m | Avoid if able |
| Device | Avg W | Peak W | Note |
|---|---|---|---|
| 1080p Cam | 5 | 8 | IR on |
| Wi-Fi AP | 10 | 16 | Ceiling |
| VoIP Phone | 3 | 6 | Desk use |
| PTZ Cam | 18 | 28 | Heater load |
| Scenario | Devices | Budget | Note |
|---|---|---|---|
| Small camera wall | 4 | 120 W | Safe headroom |
| 6 AP cluster | 6 | 180 W | Near limit |
| Mixed office edge | 20 | 300 W | Watch reserve |
| PoE++ mini PC | 1 | 90 W | Use bt4 |
Power over Ethernet (PoE) allow both data and power to travel along a single Ethernet cable. Implementing PoE technology require planning to ensure that the power budget of the PoE switch can meet the power demands of the networked devices. Many people make a mistake of calculating the power budget of a PoE switch based off the average power consumption of the devices connect to the switch.
However, the power budget of a PoE switch must be calculated according to the peak power consumption of the devices. The peak power consumption of a device is the amount of power the device use during a task that requires the most power from that device. Devices that reach their peak power consumption will drain the power budget of the PoE switch too quick.
How to Plan Power for a PoE Network
For example, a pan tilt zoom (PTZ) camera will use more power when it is moving than when it is not moving. Thus, the power budget for a PTZ camera must account for the power that it require to move. The type of Ethernet cable that is used in a PoE installation can also affect the power that reach the networked devices.
If the Ethernet cable has thinner conductors, the electrical resistance within the cable will increase. As a result, some of the power will be lost as heat along the length of the cable. The voltage of the data signal will drop along the cable, and the device at the end of the cable may not recieve enough voltage to function correct.
For these reasons, high quality Cat6 cabling is the best choice for PoE networks. Cat6 cabling can handle the power that the cable delivers to the networked devices more efficient than cheaper alternatives, such as copper clad aluminum (CCA) cabling. Because copper clad aluminum (CCA) cabling has higher resistance than Cat6 cabling, it is more likely to cause voltage drops along the length of the cable.
Another factor to consider in the implementation of a PoE network is including a reserve margin in the power budget of the PoE switch. The reserve margin is extra power that a PoE switch allocate for its devices that it does not use. A PoE switch should include a reserve margin of 15 to 20 percent of its total power budget.
By including a reserve margin, a PoE network can be expanded in the future by adding new network device to the network without exceeding the total power budget of the PoE switch. If there is no reserve margin in the power budget of a PoE switch, adding even a single device to the network will likely cause the switch to exceed its power budget. Should the device exceed the power budget of a PoE switch, the device will lose power or fail to function altogether.
The data sheets for PoE device will list the power that the device will use when it is idle. However, the power that a device consume when it is idle isnt the same as the power that the device will use when it is performing its tasks. Thus, the power consumption of a device from the data sheet is not the power that should of been used to calculate the power budget for a PoE switch.
Furthermore, the PoE switch (Power Sourcing Equipment or PSE) must provide more power than the data sheet for the networked device (Powered Device or PD) indicate will be used in operation because some of that power will be lost to heat within the Ethernet cabling. Thus, if the power loss in the cabling is ignored when calculating the total power that the PoE switch should provide to the devices, the calculation will be inaccurate; inaccurate calculation will lead to power failures in the devices. Finally, it is essential to track the total wattage of the PoE switch and the total number of available port on the PoE switch.
A PoE switch may have enough total wattage to power the number of devices that are currently connected to the switch; however, the PoE switch may not have enough available ports for those device. Alternatively, a PoE switch may have many available ports that are empty of devices; however, the PoE switch may not have enough total wattage to power any additional device that may be added to the network. Thus, it is essential to account for both the total wattage and the total number of available ports on a PoE switch to ensure that the PoE switch can support the device that are to be part of the PoE network.
