A well-planned PoE scheme runs for years; a badly planned one drops channels on winter nights.

1. Know the standards: 802.3af delivers 15.4 W per port (about 12.95 W usable), 802.3at delivers 30 W (about 25.5 W usable). PTZ heads, heaters and high-power illumination usually need at or bt.
2. Budget on peak draw: IR LEDs and pan-tilt movement draw far more than the idle figure. Plan for at least 1.3 times the rated consumption per device, and leave a further 20% of switch capacity in reserve.
3. Account for voltage drop: the longer the PoE run, the greater the drop. Keep single runs under 90 metres, and near that limit use heavier-gauge oxygen-free copper cable.
4. Do not oversubscribe: once a switch's total PoE budget is exhausted, new devices cycle on and off and channels drop randomly. Reallocate ports by priority.
5. Thermal design: PoE switches run hot at full load. Cabinets need real ventilation so thermal protection does not take the whole rack down.

A planning tip: list each position's model and consumption in a table and add them up item by item before choosing a switch. It is far more reliable than estimating by feel.