Every IP camera, access point, phone, and sensor installed on a building network today requires two things: a data connection and a power connection. Before Power over Ethernet, that meant two cable runs to every device — a Cat5e/Cat6 data cable to the IDF room and a 240V mains circuit to the nearest electrical distribution board, with an electrician required for the latter. For a building with 500 IP cameras, 200 access points, and 300 VoIP handsets, that mains circuit installation represents a significant fraction of the total project cost and programme.
IEEE 802.3bt Type 4 — commonly called PoE++ — changes this calculation fundamentally. 90W over a single Cat6A cable is sufficient for every device that a data network port services, with the exception of desktop computers and monitors. The building's structured cabling plant becomes the power distribution network for every networked device in the building — and the IDF switch replaces the electrical distribution board as the point of power control, monitoring, and management for that entire device population.
IEEE 802.3 PoE Standards Comparison
| Standard | PSE Power | PD Power (at device) | Wire Pairs Used | Max Distance | Typical Powered Devices |
|---|---|---|---|---|---|
| IEEE 802.3af (PoE) | 15.4W | 12.95W | 2 pairs | 100m Cat5e+ | IP phones, basic IP cameras, small APs |
| IEEE 802.3at (PoE+) | 30W | 25.5W | 2 pairs | 100m Cat5e+ | PTZ cameras (small), 802.11n/ac APs, VoIP dect |
| IEEE 802.3bt Type 3 (PoE++) | 60W | 51W | 4 pairs | 100m Cat6A | Wi-Fi 6E APs, mid-range PTZ, LED controllers |
| IEEE 802.3bt Type 4 (PoE++) | 90W | 71.3W | 4 pairs | 100m Cat6A | PTZ+heater/wiper, Wi-Fi 7 APs, thin clients, digital signage |
PoE++ System Design Essentials
- Power budget calculation: Total PSE power budget = Σ (PD watts × simultaneous device count) + cable losses (≈20% of PSE output). A 48-port 802.3bt switch with 1440W total budget can supply: 16 cameras at 90W, or 36 Wi-Fi 7 APs at 40W, or mixed loads calculated to the total budget
- Cable thermal management: TIA-568.2-D PoE amendment mandates derating for bundled runs — Cat6A: no derating required for bundles up to 192 cables at 90W per cable at 45°C ambient; Cat6: derating required above 24 cables in a bundle at full load
- UPS sizing for PoE loads: IDF switch PoE loads must be included in UPS calculations — a fully loaded 48-port PoE++ switch draws 1440W from the switch power supply. UPS specifications must cover switch + PoE load, not just switch idle power
- LLDP MED power negotiation: Managed 802.3bt switches use LLDP MED (Media Endpoint Discovery) to negotiate per-device power allocation — allocating only the power class requested by each device rather than reserving 90W for every port regardless of device type
- 4-pair PSE mode: 802.3bt Type 3 and Type 4 use all four pairs of Cat6A for power delivery (dual-signature or single-signature modes) — requiring 4-pair PSE capability in the switch and 4-pair PD capability in the device. Legacy PoE injectors and midspans typically support only 2-pair power
- IEC 62368-1 safety: High-power PoE at 90W requires compliance with IEC 62368-1 (Audio/Video, Information and Communication Technology Equipment safety) which governs power source energy limits — devices and infrastructure must carry relevant safety certification
Multi-Gigabit PoE: 10G Data + 90W Power Over Cat6A Simultaneously
IEEE P802.3df (under development) will standardise multi-gigabit PoE — delivering 2.5G, 5G, and 10G data simultaneously with 90W PoE power over a single Cat6A cable. The current 802.3bt standard supports only 1G data alongside 90W power — a limitation becoming visible as Wi-Fi 7 access points with aggregate radio throughputs exceeding 5 Gbps require backhaul connections beyond 1G. P802.3df resolves this, enabling the LAN switch to deliver true 10G backhaul and 90W power to the most demanding future Wi-Fi 8 access points over the Cat6A cabling infrastructure already installed. As LED luminaires, occupancy sensors, and environmental monitors all converge on PoE connectivity, the structured cabling plant becomes the primary power distribution network for the intelligent building — with the LAN switch managing both data and power for the full device population.