Field note · 7 min
How to budget PoE power for security cameras
PoE design has two gates: each port must support its camera, and the switch must deliver the sum of all active loads. A port count alone proves neither.
Start from worst configured device state
A camera that uses modest power in daylight may draw more when IR LEDs, white light, a heater, a wiper, audio, or an accessory activates. Use the exact model’s maximum specification for the features that will be enabled. Typical consumption is useful for energy estimates, not for proving capacity.
For mixed cameras, total each group separately. A few high-power PTZ or heated cameras can dominate a switch that otherwise looks comfortable.
Pass both the port and total tests
The per-port test asks whether one port and its PoE standard/class can supply one device. The total test sums all planned device loads and compares that with the switch’s PoE budget. Add a visible project margin rather than silently inflating camera wattage.
- Device requirement and supported PoE standard
- Port-specific watt/class capability
- Total switch PoE budget
- Power-supply and temperature derating
- Cable length, conductor size, and installation conditions
- Startup, sequencing, and future expansion
Why a nominal 150 W switch is not a 150 W camera system
The published PoE budget is the relevant output figure; the switch’s AC input or power-supply nameplate is not interchangeable. Some switches offer different budgets depending on the power supply, redundancy mode, or ambient temperature. Certain port groups may share constraints.
If planned camera draw with headroom exceeds the available budget, options include a larger power supply, an additional switch, a compliant midspan/injector design, or redistributing high-power devices. The right answer depends on the system architecture.
Bring the UPS into the same conversation
Keeping cameras powered while the recorder or uplink is down may not meet the operational goal. Estimate runtime using the AC load of the whole critical path and the UPS manufacturer’s runtime curve, not only the sum of PoE device watts.
Document which devices must survive an outage and for how long. Test graceful shutdown and power recovery. Power budget proves capacity; it does not prove resilience.
Sources and further reading
The article distinguishes arithmetic from professional design judgment. Primary and technical sources:
IEEE 802.3bt-2018 ↗
Primary PoE standard reference.
Ethernet Alliance PoE resources ↗
Interoperability and certification context.