PoE explained: the number that decides how many cameras your switch can run

Power over Ethernet means a camera takes its power from the same cable that carries its video. One cable per camera instead of two, no socket at each position, and no separate adapter to fail. It is the main practical reason cabled systems moved to IP.

The two standards you will meet

• 802.3af (PoE) — up to about 15.4 W per port. Enough for almost any fixed bullet or dome camera.
• 802.3at (PoE+) — up to about 30 W per port. What you need for a motorised PTZ camera, or a camera with strong illuminators or a heater.

A PoE+ camera on an af switch may run and then fail when it tries to move or turn its lights on — which looks like an intermittent camera fault and is actually a power fault. Worth knowing before you spend an afternoon on it.

Power budget is the real limit

This is the number people miss. A switch has a total PoE budget shared across all its ports, and it is usually well below port count times the per-port maximum.

An 8-port PoE switch with a 63 W budget — like the Tenda TEF1110P — will happily run eight cameras drawing 6–7 W each. It will not run eight cameras drawing 12 W each, even though it has eight ports and each port is capable of it. Add up your cameras' actual consumption from the spec sheet and leave headroom.

Distance

100 metres from switch to camera, on proper cable. That is the standard and it is not negotiable by wishing. Beyond it you need a switch or a PoE extender in between.

"Proper cable" matters more than people expect: aluminium-cored cable sold as CAT6 has higher resistance, and the symptom is a camera that works at 40 m and not at 80 m. If a long run is unreliable, suspect the cable before the camera.

What to buy

For a camera system, buy the switch after you have chosen the cameras, add up the wattage, and pick a budget with room for one more camera than you are fitting. There is always one more camera. Browse PoE and network switches, and if you would rather not do the arithmetic, send us the camera models and we will do it.