— PoE Budget · Networking
Office floor closet — 38 PoE devices, 416 W pool
Problem. A single office floor's comms closet has to power a mix of Wi-Fi 6 access points, fixed cameras and desk phones from one PoE switch. The question is not whether any single port can drive its device — they all sit inside PoE+ limits — but whether one switch's shared power pool can carry the whole floor at once.
Answer. Six Wi-Fi 6 APs at 18 W, twelve fixed cameras at 6 W and twenty VoIP phones at 7 W total 320 W of device draw; with the tool's 30% design headroom that becomes 416 W, which clears the 380 W single-24-port budget and lands on a 48-port L2 managed PoE+ switch (740 W pool). The tier here is set by the aggregate pool, not by any one hungry port.
02 / In depth
How this preset reads — the engineering view.
PoE sizing has two independent floors. The per-port floor asks what IEEE class the single hungriest device needs at the powered-device (PD) end — 802.3af at or below 12.95 W, PoE+ at or below 25.5 W, 802.3bt Type 3 at or below 51 W, Type 4 at or below 71 W. The aggregate floor asks whether the switch's shared power pool covers the sum of every device plus a 30% design margin. The recommended tier is the higher of the two, because a switch that fails either test cannot run the floor.
For this closet the device load is 6×18 + 12×6 + 20×7 = 108 + 72 + 140 = 320 W. Adding 30% headroom gives 416 W. The hungriest device is an 18 W Wi-Fi 6 AP, which sits inside the 25.5 W PoE+ PD ceiling, so the per-port floor is only PoE+ and does not push the tier up. The 416 W pool, however, exceeds the 380 W that a 24-port PoE+ switch offers, so the aggregate floor selects the 48-port L2 managed PoE+ class with a 740 W shared pool across 38 powered devices.
The result moves with total wattage: add more APs, cameras or phones and the 416 W figure climbs monotonically toward the 740 W ceiling and eventually into a higher tier. Swapping a fixed camera for an IR or PTZ head raises both the per-device draw and, if the largest device crosses 25.5 W or 51 W, the per-port class floor as well. Nothing you add lowers the requirement — the pool only grows.
The tool sizes the power pool and the port class; it deliberately does not lay out cabling runs, model Cat6a distance derating, size uplinks or redundancy, or account for simultaneous-peak versus average draw beyond the flat 30% margin. It assumes one logical switch stage — real floors may split load across stacked units or distribution closets, and standby PoE for critical devices is a design choice made outside this estimate.
What this preset deliberately does not solve
- Models a single shared power pool, not multi-switch stacks or uplink sizing.
- The 30% headroom is a flat design margin, not a measured peak-versus-average profile.
- Device wattages are conservative typicals; verify each PD against its own datasheet.
How this preset differs from its siblings
This preset is aggregate-driven: every device sits inside PoE+, so the tier is set purely by the summed 416 W pool. Its sibling, the perimeter PTZ drop, is the opposite case — a small total load whose single 55 W heated PTZ forces a Type 4 tier on the per-port floor. Use this one to reason about how many devices a shared pool can carry; use the perimeter preset to see how one demanding device dictates the switch class.
03 / Hydrated calculator
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