When to use: Verify a PoE switch's total power budget against the connected powered devices. The per-port figures (15.4 W af, 30 W at, 60/90 W bt) are the power sourced at the switch (PSE) and already include worst-case 100 m cable loss, so summing PSE watts gives the switch-side demand. Keep the total at or below the rated power budget with margin for simultaneous draw.
This calculator verifies whether a PoE switch's total power budget can support all connected powered devices across IEEE 802.3af, at, and bt PoE classes. It is used during network design to confirm switch selection and prevent power budget oversubscription.
A PoE switch allocates power to each port according to the PoE class negotiated during the IEEE 802.3af/at/bt handshake. The Power Sourcing Equipment (PSE) side of the switch must reserve the maximum class power per port: 15.4 W for 802.3af, 30 W for 802.3at (PoE+), 60 W for 802.3bt Type 3, and 90 W for 802.3bt Type 4.
The total PSE power drawn is the sum of all per-port allocations. This must not exceed the switch's rated PoE power budget. The PSE figures already include worst-case cable loss over a 100 m channel, so summing PSE watts directly gives the switch-side demand without needing separate cable loss calculations.
Most switches allow simultaneous full PoE delivery on all ports only if the total power budget is not exceeded. Many lower-cost switches have a total PoE budget (e.g. 370 W on a 24-port switch) that cannot power all ports simultaneously at full class wattage — this tool identifies that condition.
IEEE 802.3af (2003) defines PoE Type 1 at 15.4 W PSE / 12.95 W PD over two pairs. IEEE 802.3at (2009) defines PoE+ Type 2 at 30 W PSE / 25.5 W PD. IEEE 802.3bt (2018) defines PoE++ Type 3 (60 W PSE / 51 W PD over four pairs) and Type 4 (90 W PSE / 71.3 W PD). NFPA 731 addresses installation requirements for security systems including power supply reliability for PoE-powered security devices.
Maintain at least 10–20% headroom on the switch PoE budget for simultaneous peak draw and future device additions. Switches often limit the per-port power to the negotiated class allocation, which means a device drawing less than its class maximum still consumes the full class reservation on the switch budget.
For critical security applications such as cameras and access control, use a dedicated PoE switch on an uninterruptible power supply (UPS). If the total device load exceeds one switch's budget, split device groups across multiple switches or use PoE midspan injectors for the highest-draw devices. Verify that the switch backplane has sufficient non-blocking throughput for the aggregate camera bandwidth.
Enter the switch's total PoE power budget in watts (from the switch datasheet) and add each device type with its PoE class and quantity. The tool sums the PSE-side power allocation for all devices and checks it against the switch budget, showing utilization percentage, headroom in watts, and pass/fail status. If the result fails, either reduce the number of higher-class devices, split the load across a second switch, or specify a switch with a higher PoE budget.
Switch manufacturers design PoE budgets assuming not all ports will be simultaneously loaded at maximum class power. A 370 W budget on a 24-port PoE+ switch means the switch PSU can only deliver 370 W total across all ports simultaneously. If your devices require more, you must add a second switch or upgrade to a higher-budget model.
PSE (Power Sourcing Equipment) watts is the power the switch delivers at the port. PD (Powered Device) watts is what the device receives after resistive cable loss over the 100 m channel. For 802.3af: PSE = 15.4 W, PD = 12.95 W. For 802.3at: PSE = 30 W, PD = 25.5 W. Budget calculations must use PSE watts.
Yes. IEEE 802.3bt Type 3 and Type 4 switches are backward compatible with 802.3af and 802.3at devices. Each port negotiates the appropriate class during the handshake and delivers only the requested power. The switch reserves power per negotiated class, not per port maximum.
Most PTZ cameras with pan/tilt motors and zoom draw 15–30 W and require 802.3at (PoE+) class allocation. High-performance PTZ cameras with heaters or IR illuminators may require 802.3bt Type 3 (60 W PSE). Always verify the camera datasheet power consumption before specifying the switch class.
A PoE switch has an internal PSU that powers both the switch electronics and the PoE budget. The switch's rated PoE budget is the power available for PD devices only — the switch electronics consume additional power. Verify the switch's total power consumption (data + PoE) when sizing the UPS that supplies the switch.
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