PoE Design Guide for IP Camera Systems

Video surveillance is the application that made PoE mainstream, and it remains the one where power design most often goes wrong. A camera system is not a constant load: it draws far more at night than during the day, more in winter than in summer, and more during a pan-tilt movement than at rest. Designing for the datasheet's typical figure produces a system that works perfectly during commissioning in September and starts dropping cameras in January.

What Cameras Actually Draw

Camera power falls into three bands. A fixed indoor camera with no illumination is a class 2 or class 3 device drawing 4 W to 12 W. An outdoor bullet or dome with infrared illumination and a heater sits in class 4 territory, and can approach the full 25.5 W when the IR array and the heater run together. A PTZ camera adds motor loads and larger heaters, placing it in class 5 or class 6 and occasionally class 7 for units with wipers and long-range illuminators.

Camera type	Typical class	Idle draw	Worst case
Fixed indoor, no IR	2	3-5 W	6.5 W
Indoor dome with IR	3	5-8 W	12.95 W
Outdoor bullet, IR + heater	4	7-10 W	25.5 W
PTZ, heater and wiper	6	12-20 W	51 W
Multi-sensor panoramic	5-6	15-25 W	40-51 W

Budget for the Worst Case, Not the Typical

The coincident worst case for an outdoor system is a cold night: every heater on, every IR array at full output, simultaneously across the whole site. That is the number the switch must survive, and it frequently doubles the summer daytime figure. Size the switch's PoE budget against the sum of class reservations for all populated ports, and verify that the switch sheds load gracefully rather than rebooting if the budget is ever exceeded.

Distance and the Far Camera

Conduction loss scales with the square of the current, so the high-draw cameras are exactly the ones that suffer most on long runs. A class 4 camera at 95 m on 24 AWG cable can arrive with several volts less than one at 10 m, and if the camera's input regulator has a narrow window, that is the unit that resets under heater load. Where a run is both long and high-power, either move up a class at the source, use 23 AWG Cat6, or place a PoE extender or a local injector nearer the camera.

Switch Placement and Uplinks

Bandwidth planning is the other half. A 4K camera at 20 fps with H.265 will average somewhere in the 8 to 16 Mbps range and spike well above it during scene changes; twenty-four such cameras can saturate a gigabit uplink during a storm when every frame is full of moving foliage. Specify a 10 Gbps uplink for any edge switch carrying more than roughly sixteen 4K streams, and keep the recorder on the same aggregation layer so video does not traverse the core unnecessarily.

Redundancy and UPS Runtime

A surveillance system that dies with the mains is of limited value in exactly the circumstances it exists for. Calculate UPS runtime against the winter worst-case load rather than the idle figure, and consider whether heaters can be shed on battery - many cameras will run for hours on battery if the heater is disabled, and minutes if it is not. Managed switches with per-port priority make this practical: mark the critical camera ports high priority and let the rest drop.

Commissioning Checks

Before handover, force the failure conditions rather than waiting for them. Enable every heater and IR array simultaneously and confirm the switch holds. Measure delivered voltage at the two or three longest runs under that load. Power-cycle the switch and verify every camera returns without manual intervention, since inrush at simultaneous restart is its own stress case. Record per-port consumption from the switch as a baseline; a camera whose draw drifts upward over months is usually a failing heater or an ingress problem, and catching it from the switch statistics is far cheaper than a lift hire.

Common Failure Patterns

Three recur across sites. Cameras that reboot only at night are power-starved by IR load. Cameras that fail only in winter are heater-related and almost always a class or distance problem. And a whole branch dropping simultaneously points at a shared extender, injector or switch that is running at its budget limit rather than at any individual camera.