Warehouse PoE and Cabling Standard Mismatch
A warehouse is replacing 12 handheld-scanner access points. The new APs specify 802.3bt Type 3 (60 W at the PSE, 51 W at the PD), 2.5GBASE-T, and are mounted 85 m from the IDF along cable trays that share a conduit with forklift battery chargers. The existing access switch is a 24-port Gigabit model with 802.3af on all ports and two 10G SFP+ uplinks. A vendor proposes using the existing Cat5e cabling and adding a 24-port 802.3af PoE injector midspan. Facilities wants to avoid re-cabling; the network team is concerned about heat in the ceiling and future Wi-Fi 6E. Budget allows either new cable or new switches, not both. The pilot AP reboots under load, and the link negotiates at 1 Gbps, not 2.5 Gbps.
1. The vendor says the 802.3af midspan is sufficient because the AP average draw is 12 W. Is that compliant and safe? Identify the standard mismatch and the minimum power and cabling plan you would approve.
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No, the midspan is not compliant for this AP. 802.3af caps the PSE at 15.4 W and the PD at 12.95 W. The AP's 51 W PD requirement is nearly four times that limit; average draw is irrelevant because startup, radio transmit bursts, and PoE classification must fit the standard. A compliant plan needs an 802.3bt Type 3 PSE (60 W) or Type 4 (90 W) and a PD that advertises the correct class. The vendor's 802.3af midspan cannot negotiate 51 W and may cause repeated boots or port power denial.
For cabling, 85 m of Cat5e is within the 100 m channel for 2.5GBASE-T, but the shared conduit with battery chargers makes EMI and bundled-cable heating real risks: 12 ports at 60 W is 720 W of PoE. I would approve an 802.3bt switch with 2.5GBASE-T ports first, then require cable certification and CRC/error testing. If the Cat5e fails, shielded Cat6A or fiber is the fallback. Since budget allows only one major spend, replace the switch now and stage the cable remediation.
2. The pilot AP links at 1 Gbps and reboots. Explain the two independent causes and the measurements that would distinguish them.
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Two independent causes are in play. The 1 Gbps link is a speed-negotiation result: the AP is 2.5GBASE-T and the switch port is 1000BASE-T, so the highest common speed is 1 Gbps. That alone does not reboot the AP. The reboots point to power: the PSE offers 802.3af power while the AP needs 51 W at the PD. Under load the AP may brown out or reset when the radio draws peak current.
To separate them, measure the actual PoE class and wattage at the PSE and at the PD, for example with an inline PoE tester or the switch power-via-MDI/LLDP data. Then check the AP boot log for power-related resets. For the link, confirm the negotiated speed and the switch port capabilities; a 2.5GBASE-T port should show 2.5 Gbps. Also run cable certification for insertion loss, return loss, and CRC errors because the EMI environment can create errors that look like power resets. Fix power first, then speed.