PoE Budget Exhaustion After Adding Wi-Fi 6 APs

Start with the existing state. Forty APs at the 30 W maximum is 1,200 W. Eight cameras at 12.5 W is 100 W, so worst-case existing load is 1,300 W. At the AP typical value of 18 W, forty APs draw 720 W, plus 100 W for cameras, for 820 W. Both numbers already exceed the 740 W budget, which explains why the switch is logging power denied events even before the ten new APs are considered. The existing system may have survived only because some APs negotiated 15.4 W and because not all APs drew their maximum simultaneously. Now add ten APs. At 30 W maximum, fifty APs draw 1,500 W, plus 100 W cameras, for 1,600 W. At 18 W typical, fifty APs draw 900 W, plus 100 W cameras, for 1,000 W. Even if every AP negotiated only 15.4 W, fifty APs draw 770 W, plus 100 W cameras, for 870 W. There is no realistic configuration in which fifty APs plus eight cameras fit within 740 W. Adding the APs is not safe. The reboots are not a firmware bug; they are the switch shedding or denying power when the budget is exceeded. The LLDP value of 15.4 W is a symptom: the switch is advertising or granting 802.3af-level power, so APs may be underpowered or falling back.

LLDP power negotiation depends on both sides. The switch advertises its available power and power class through LLDP-MED or 802.3at LLDP extensions, and the AP requests a power level. If the switch port is configured for 802.3af, if LLDP is disabled, if the power budget is exhausted, or if the switch caps the port to a lower class, the AP may receive 15.4 W instead of 25.5 W. Some APs also fall back to a lower power mode when they do not receive the expected LLDP grant. The team should check the per-port PoE status, the advertised and requested power in LLDP, the port power limit, and whether the switch is using Class 4 or Type 2 negotiation. They should confirm that the AP supports LLDP and that LLDP is enabled on the port. They should also check whether the switch is in a static power mode rather than dynamic negotiation. However, fixing LLDP alone will not solve the problem because the total budget is already insufficient. Raising ports to 25.5 W would increase the shortfall. The team must first add power capacity, then verify that APs negotiate the intended class. If the AP can operate with reduced features at 15.4 W, that may be a temporary measure, but it should be validated against the AP datasheet and the required radio configuration.

The first priority is to stop adding APs and prevent random reboots. Remove the ten new APs or move them to another switch with available budget. The second priority is to add power capacity. If the switch supports a second 740 W supply, install it and verify that the combined budget is actually available for PoE, not just for system power. A second supply may bring the budget to 1,480 W, which covers the 1,000 W typical load but not the 1,600 W worst case. For a production design, size for worst case or for a documented diversity case with margin. If the switch does not support a second supply or the combined budget is still insufficient, split the APs and cameras across two switches or replace the switch with a higher-budget PoE platform. The third priority is to configure per-port power priority so APs are critical and cameras are lower priority, but understand that priority does not create watts; it only decides who loses power last. Fourth, validate LLDP and 802.3at negotiation on every AP port and record actual draw. Fifth, add monitoring for PoE budget utilization, power denied traps, and per-port power. Sixth, obtain UPS capacity data and size the UPS for the switch, APs, and cameras at the new load. A UPS that cannot carry the PoE load will fail at the worst time. Finally, document the power budget in the change-management process so future AP additions are checked before they are connected.