PoE Budget Exceeded After Camera Addition
A 24-port PoE+ access switch has a 370 W PoE budget. Currently 18 ports are in use: 12 VoIP phones (Class 4, ~7 W each), 4 802.11ac APs (Class 4, ~13 W each), and 2 PoE cameras (Class 4, ~12 W each). The facilities team wants to add 6 more PoE cameras of the same model. The switch reports PoE usage near 200 W at peak. The customer also wants to add a second uplink 'for redundancy' using a spare copper port. Ports 23-24 are currently the only free ports besides the new camera drops.
1. Determine whether the PoE budget supports the additional cameras and show the arithmetic.
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Current draw: 12×7 = 84 W; 4×13 = 52 W; 2×12 = 24 W → 160 W allocated, with ~200 W peak reported (allocation vs. actual can differ; use the higher figure for planning).
Adding 6 cameras at ~12 W = 72 W. New allocation: 160 + 72 = 232 W; peak could approach 200 + 72 = 272 W.
Against a 370 W budget, 272 W leaves ~98 W headroom, so the budget itself supports the cameras - but only if the switch's per-port and total allocation logic allows it and if the peak estimate holds. The judgement call: PoE power is sufficient, but the port count and uplink plan are the real constraints, and the peak figure should be re-measured after install rather than assumed.
2. The customer asks to use ports 23-24 for the new cameras and the spare copper port for a redundant uplink. Evaluate this plan.
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The plan is internally inconsistent and should be rejected as stated:
- 6 new cameras need 6 free ports, but only ports 23-24 are free (2 ports). The plan cannot physically accommodate the cameras without freeing ports or adding a switch.
- Using the last free copper port for a 'redundant' uplink gives two uplinks with no LACP or spanning-tree design stated; a naive second link can create a loop or an unmanaged active/standby that provides no real redundancy. Redundancy requires LACP (active/active) or STP with a defined root/blocking behavior.
- PoE-wise the cameras fit, but only after port capacity is solved.
Recommended: add a second PoE switch (stack or uplink) for the cameras, or reclaim ports by moving phones to a non-PoE switch if they are locally powered; design the uplink as an LACP bundle with the distribution switch rather than an ad hoc second cable.