Power over Ethernet is a standard that allows network cables to carry both data and electrical power simultaneously. This means a single Cat5e or Cat6 Ethernet cable can connect a device and power it, rather than requiring a separate mains cable or power adapter.
How it works: PoE injects low-voltage DC power (typically 48V) into unused wire pairs within the Ethernet cable. A PoE injector or PoE-enabled network switch supplies the power, whilst the receiving device (the powered device) draws what it needs.
Common use cases:
- IP security cameras in difficult-to-wire locations
- Wireless access points on ceilings or walls
- VoIP phones
- Network switches and hubs
- Smart lighting and environmental sensors
Power standards to know: PoE (IEEE 802.3af) provides up to 15.4W, adequate for most cameras and access points. PoE+ (802.3at) offers up to 30W. High-power variants like PoE++ (802.3bt) deliver up to 90W, suited to devices like powered video displays.
Practical benefits: Reduces installation costs by avoiding dedicated power circuits. Simplifies cable runs through walls and cable trays. Allows centralised power management from the network switch, and many switches support power scheduling or failover.
Common gotchas: Cable length matters. PoE performance degrades over distances beyond 100 metres, the standard Ethernet limit. Passive PoE injectors lack power negotiation and can damage unprepared devices. Always check your device's power requirements match the available PoE standard.