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PoE budgets are consumed by class allocation rather than measured draw on many switches, so 36 Type 3 devices can reserve 2,160 W even if they actually use 60 percent of that. Where LLDP power negotiation is supported, allocation tracks real demand more closely — but a switch that reserves by class will refuse power at boot once the budget is committed.
PoE sizing
worst case = devices x class maximum; expected = worst case x average draw share; devices supported = floor(budget / class maximum)
Because it must guarantee power if the device demands it. LLDP-based negotiation allows a finer allocation, but not all powered devices support it.
Yes. The standard accounts for up to 15 to 20 percent loss in a 100 m run, which is why port power at the switch exceeds the power available at the device.