What is “PoE?”

I know what you’re thinking, PoE is a 19th century horror writer best known for “The Raven?” What, you’re not thinking that? Perhaps you’re not a high school English teacher. After all, there are a limited number of them.

PoE is an acronym standing for Power over Ethernet. Don’t ask me why the “o” in “over” isn’t capitalized, let’s be honest I’m having a hard enough time keeping on topic here.

Power over Ethernet is a way that access points, cameras and other devices can work without being near a power outlet. The Ethernet cable itself carries power on two wires which would otherwise not be used. Therefore, a device that’s plugged into a PoE cable doesn’t need a separate power cord. This makes installation easier and means that something like a security camera can be placed almost anywhere that a single Ethernet cable can reach. The voltage is very low – typically 24 volts – so that there is little danger in running cable through any space. 24 volts shouldn’t generate excess heat or create any problems in an otherwise safe installation.

PoE usually requires a “PoE injector” which plugs into an outlet. An Ethernet cable goes to the router or switch, and another Ethernet cable, containing power, goes out to the device that needs it. We have a decent selection of them here, and you can also buy industrial routers and switches that have this feature built in.

It’s always best to make sure that a PoE line is not used for a regular Ethernet connection. While most PoE injectors will only power the line if it is needed, there is always a possibility that a device will receive 24 volts over the Ethernet cable when it doesn’t need it. For that reason you should always make the effort to tag PoE cables so someone working with your system in the future will know that they are there.

About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 9,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.