The most common commissioning fault we see is not a bad camera — it is a switch quietly running out of power. PoE budgets fail at the worst time: cold nights, when IR arrays and heaters all draw at once.
Add up worst-case, not nameplate-average
A varifocal bullet that idles at 6 W can pull double that with IR on and the lens motor running. Budget every port at its class maximum — 802.3af ports at 15.4 W, 802.3at at 30 W — and the winter surprise disappears.
Keep a quarter in reserve
Design the load to 75% of the switch’s stated budget. The margin absorbs firmware changes, replacement cameras with hungrier IR, and the PTZ someone adds next year.
Long runs change the math
Extend mode and long cable runs lose real watts to resistance. Past 100 meters, assume 10–15% of the power never arrives, and prefer a mid-span injector over pushing a marginal run.
One budget line per closet
Write the per-port draw into the camera schedule and total it per switch. The document takes ten minutes and turns every future fault call into a checklist instead of a mystery.
