How it works
PoE carries electrical power and network data through compatible Ethernet cabling. A switch or injector supplies power to a supported device such as an access point or camera. Standards-based systems identify and negotiate suitable power delivery; different PoE standards provide different capabilities, so the device and supply must match.
Important differences and limits
A port’s capability is separate from the total switch power budget. Several devices may exceed the available budget even when each port individually seems adequate. Non-standard passive power arrangements are not automatically compatible with negotiated PoE. Cable quality, length and environmental protection also affect a reliable installation.
A useful practical check
Check the exact powered device’s required standard and maximum demand. Verify both the per-port specification and combined power budget, including startup or optional functions. Use appropriate intact cabling and document which supply feeds each device. If a device repeatedly restarts, investigate power allocation and cabling rather than immediately blaming its network configuration.
An example in practice
For example, three devices requesting 25 watts each need 75 watts in total before other allowances are considered. A hypothetical 60-watt budget cannot supply that demand merely because every port supports one device. Calculate the combined requirement from the actual device specifications.