Hardware & Endpoints
PoE (Power over Ethernet)
By Myroslav Orshak · operates licensed carrier infrastructure · Updated September 2026
PoE (Power over Ethernet) delivers electrical power through the same network cable that carries data, so a desk phone, camera or access point needs only one cable instead of a network lead plus a power adapter.
How it works
A PoE-capable network switch puts a small voltage onto spare capacity in the Ethernet cable. The device at the other end draws what it needs, and the switch negotiates with it first, so plugging in something that does not want power is harmless. One cable to each desk carries both the call and the electricity to run the phone.
The standards differ mainly in how much power they deliver: the original 802.3af provides up to about 15 watts per port, 802.3at (often called PoE+) about 30, and 802.3bt more again for demanding devices. Desk phones are undemanding — most sit comfortably inside the original standard, which is why almost any PoE switch will run an office full of them.
Choosing a PoE switch comes down to three numbers. Count the devices you need to power, multiply by the wattage each draws (the phone's spec sheet lists it; 5 to 7 watts is typical for a desk phone), and add about a fifth for headroom. That total is the power budget to look for. Then check that the port count covers every device, plus a couple spare. Finally, decide whether you need a managed or smart switch. You do if you plan to put phones on their own network segment (a voice VLAN), so calls don't wait behind file downloads.
Why it matters
For a business installing phones, PoE removes a power adapter and a spare socket at every desk. That sounds minor until you are wiring twenty desks, at which point it decides how tidy the installation is and how much electrical work it needs.
It also makes it simpler to keep phones running in a power outage: put one UPS on the switch and every phone it feeds stays up, instead of buying twenty small ones. The trade-off is that the switch becomes a single point of failure — if it goes down, so does every phone attached to it.
IP desk phones typically draw 3–7 watts each, well inside 802.3af's ~15 W per port. What limits you is the switch's total power budget, not the per-port rating: a switch rated 65 W total cannot power 24 phones at once regardless of how many PoE ports it has.
Related terms
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Compare phone systems and their hardware →Frequently asked questions
Do I need PoE for VoIP phones?
No — every IP desk phone can run from a power adapter instead. PoE just removes one cable and one socket per desk. For a handful of phones it barely matters; for a full office it is the difference between a tidy installation and twenty power bricks under twenty desks.
Which PoE standard do I need for desk phones?
The original 802.3af is enough for essentially all of them, since phones draw only a few watts. Buying a PoE+ (802.3at) switch is still sensible if the same switch might later power Wi-Fi access points or cameras, which are much hungrier.
How many phones can one PoE switch power?
Look at the switch's total power budget rather than its port count — that is the number people get wrong. At roughly 5 watts per phone, a switch with a 65 W budget comfortably runs a dozen phones but not twenty-four, even if it has twenty-four PoE ports.
Will my phones work in a power outage?
Only if the switch has power, since it is what feeds them. That is actually convenient: one UPS on the switch keeps every attached phone alive. Your internet connection needs backup power too, or the phones will be powered but unable to reach the outside world.
What PoE switch do I need for ten desk phones?
Ten phones at around 6 watts each is 60 watts; add a fifth for headroom and look for a switch with at least 72 watts of total PoE budget and ten or more PoE ports. A 16-port model leaves room to grow. If you want phones on their own voice network segment, choose a smart or managed switch rather than an unmanaged one.
Managed or unmanaged?
Unmanaged is fine for a handful of phones on a quiet network. Once the office also runs video calls, backups and cloud sync, a managed or smart switch lets you give voice its own segment and priority, which is the cheapest reliable fix for choppy calls. The price difference for a small office is usually modest.