A PTZ camera is three loads wearing one housing: a camera, a motorised head, and — on outdoor models — a heater, blower and infrared array. Each load peaks at a different moment, and the sum at the worst moment is what the power supply must deliver. This is why PTZ cameras break more PoE designs than any other common device, and why 'it worked on the bench' is not evidence: the bench test rarely runs the heater at −10 °C with the head slewing and the IR at full power. Sizing an injector for a PTZ is an exercise in worst cases.
Start from the camera's maximum, not its typical
Camera datasheets quote power several ways, and the marketing line is never the one to design to. Look for the maximum consumption figure — often stated with heater on — and design to that. A camera quoted at '12W typical, 25W max (heater)' is a 25W load. Add the physics of the cable: the powered device must receive its power after the cable's own losses, which is why the standards define power at the PSE with headroom over what the PD is guaranteed. The injector classes in a modern catalogue — 30W (802.3at), then 60W, 90W and 100W in the 802.3bt family — exist in steps; the correct step is the first one that covers the camera's maximum with margin, not the one that covers its idle draw.
When the camera is a bt device, the injector must be one too
High-end PTZs increasingly specify 802.3bt (PoE++) outright, because their worst case exceeds the 30W that 802.3at can guarantee at the device. An at-class injector cannot negotiate a bt device into its high-power mode; the camera will either refuse, run derated, or — worst of all — run until the heater cuts in on the coldest night of the year. The injector families built for this class document it plainly: 802.3bt models at 60W, 90W, 95W and 100W, including AI Smart Managed units with LED-screen readouts and mini industrial models with voltage boosters. If the camera's datasheet says bt, the injector conversation starts on that shelf.
The input side is where outdoor PTZ designs actually fail
A PTZ on a pole or a cabinet is rarely fed from a mains rack. Its injector is fed from the site's DC plant — 12V or 24V batteries, a vehicle system, a solar-charged bank — whose voltage swings with charge state and temperature. Two injector disciplines follow. First, the input window: industrial injector families document wide windows (12–48V is the common printed pattern) precisely so the unit rides the plant's real swing. Second, the voltage booster: PoE++ delivery needs a higher rail than a 12/24V plant provides, and booster-equipped models raise it internally. An injector chosen only on its output class, fed from a plant outside its window, is a mis-specification waiting for winter.
Rate: the camera's port is part of the power decision
Modern PTZs and the multi-sensor cameras joining them can carry gigabit and multi-gig ports. The injector sits in the data path and passes only what it is rated for: a gigabit injector caps a 2.5G camera at 1G forever. The industrial families document 2.5G, 5G and 10G injector models for exactly this reason. Match the injector's rate to the camera's port, or consciously accept the cap — but do not discover it at commissioning.
Placement and the worked example
Place the injector where the power is: in the cabinet at the pole base, beside the DC plant, with the Ethernet run from injector to camera inside the standard 100 m channel. If the camera is beyond 100 m from the cabinet, the design changes species — an extender chain (budgeting power across hops) or a fiber spine with local power at the camera's cluster. Worked example, with illustrative figures: a PTZ documented at 51W maximum with heater, on a 24V battery plant, 60 m from its cabinet. The class decision: the first step above 51W with margin is the 90W bt class (60W leaves little room for cable loss and ageing). The input decision: an industrial bt model whose window covers the plant's swing, with a booster if the window's top is below delivery voltage. The rate decision: gigabit, unless the camera's port says otherwise. Three decisions, each forced by a fact about the camera or the site — that is the whole method.
Close the loop the way professionals do: the inquiry names the camera model, the plant voltage range and the distance. The quotation then confirms the injector model and class against the camera in writing. PTZ power is unforgiving of approximation, but it is entirely deterministic once the worst case is admitted.
The cold-night test, and one more failure mode
Commissioning engineers who inherit PTZ estates develop one ritual: test at the worst case, deliberately. Heater forced on, IR at full, head slewing continuously, for an hour — while watching the camera's reported input voltage if it offers one. It is a boring hour that retires a whole category of January phone calls. The related failure mode to know is the borderline negotiation: a camera that draws just inside its class at room temperature can, as cable resistance and device behaviour shift with temperature, renegotiate or brown-out at extremes. Margin is not waste in PTZ power; it is the difference between a specification and a hope. When the quotation confirms the injector against the named camera, that margin is part of what is being confirmed — ask for it by name.
Reading a PTZ datasheet like a power engineer
The datasheet's electrical section rewards a slow read. Find the input specification first: the standards it claims (af/at/bt) tell you the negotiation it expects. Then the consumption lines, plural — manufacturers often print separate figures for the camera alone, with IR, and with heater, and the largest is the design number. Then the environmental section, because the heater's duty is temperature-driven and a camera rated for −40 °C deployments is telling you its worst case lives there. Finally the port: its rate (gigabit or multi-gig) sizes the injector's data side. Four numbers — standard, maximum draw, temperature floor, port rate — and the injector specification is fully determined. Every PTZ power failure in the field can be traced to one of the four being read hopefully instead of literally.
One last placement note belongs in every PTZ power design: the injector's own environment. An injector in a sealed pole cabinet at 45 °C ambient lives a different life from its rack-mounted twin, and electronic life shortens with heat. The industrial families exist for this reason — hardened design, wide input windows, cabinet form factors — and the specification conversation should include the cabinet's thermal reality alongside its voltage. Power, rate, class, input, environment: five facts, all knowable before order, and together they are the difference between an injector that is furniture and one that is a recurring character in the maintenance log.