PoE lets a network switch or injector deliver power to a device over the spare conductors or data pairs of an Ethernet cable. Successive standards raised the budget: 802.3af for low-power devices, 802.3at for more demanding equipment and 802.3bt for higher-power loads such as pan-tilt cameras, displays and LED lighting fixtures.
For IoT in buildings the attraction is practical: one cable, one installer, centralized power that can be backed by the switch’s UPS, and the ability to reboot a stuck device by cycling its port remotely. Security cameras, Wi-Fi access points, door controllers, room sensors and smart lighting are common loads. The trade-offs are cable length limits, heat in bundled cables at high power and the cost of PoE-capable switching, which can exceed that of the devices in small deployments.
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