Separate three ratings first
- Device maximum input W: find it in the camera or AP data sheet.
- Maximum output per port: verify the required PoE type.
- Total switch PoE budget: the total available across all ports.
An eight-port switch rated 30 W per port does not necessarily provide 240 W total. Check the product’s separate total PoE budget.
Power by standard type
| Type | Standard | PSE max output | Minimum at PD |
|---|---|---|---|
| Type 1 | 802.3af | 15.4 W | 12.95 W |
| Type 2 | 802.3at | 30 W | 25.5 W |
| Type 3 | 802.3bt | 60 W | 51 W |
| Type 4 | 802.3bt | 90 W | 71.3 W |
Cable loss makes PSE output different from guaranteed power at the PD. The calculator compares device input with PD limits.
Practical checklist
- List maximum W and quantity for each device.
- Add design headroom such as 20%.
- Check total PoE budget and port count separately.
- Verify that each port supports the device PoE type.
- Be more conservative for near-100 m runs, hot bundles and heated outdoor cameras.
PoE compatibility alone does not guarantee installation quality. Check cable category, run length, connectors and ambient temperature.
Sources
- Cisco, What Is Power over Ethernet (PoE)? — evolution of 802.3af/at/bt, PSE output and cable loss.
- Ethernet Alliance, Overview of 802.3bt — 13 W, 25.5 W and 71.3 W available at the PD, plus an 802.3bt overview.
- Microchip, Next-Generation PoE — Type 4 comparison of 90 W at the PSE and 71.3 W at the PD.