Glossary · Networking

PoE (Power over Ethernet)

PoE delivers electrical power and data over a single Ethernet cable, powering devices such as IP cameras, phones and access points.

Updated October 6, 2026

PoE (Power over Ethernet) is a set of IEEE standards that deliver electrical power along the same twisted-pair cable that carries data. A PoE-capable switch or a small inline injector supplies power to a powered device (PD), removing the need for a separate power adapter and nearby outlet.

Why it matters

It simplifies installation of ceiling-mounted access points, IP cameras and VoIP phones, and allows central battery backup from one switch. Common standards are 802.3af (up to 15.4 W at the source, about 12.95 W at the device), 802.3at "PoE+" (30 W) and 802.3bt (60 W and 90 W). Switch and device negotiate power class automatically, so a non-PoE device normally is not damaged.

Example

A switch has a PoE budget of 120 W. Connecting four cameras that draw 7 W each uses 28 W and leaves 92 W for others. Adding a 25 W access point still fits; adding six more 15 W devices would exceed the budget, and some ports would be refused or shut down.

Common mistakes

  • Ignoring the total switch power budget, not only per-port limits.
  • Using cheap cable with copper-clad aluminium conductors, which loses more power and can overheat.
  • Forgetting the 100 m Ethernet length limit still applies.

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