A PoE switch is a network switch that sends electrical power down the same Ethernet cable that carries data. Plug an IP camera into it and the camera gets its network connection and its power from one cable, with no power adapter at the camera end.
That’s the whole idea, and it’s why almost every IP camera system installed in Oman in the last decade runs on one. The part people get wrong isn’t what a PoE switch is. It’s how much power it can actually give out, and that’s what drops cameras offline at 2 a.m.
How Power over Ethernet works
A Cat5e or Cat6 cable has eight wires. Data uses four of them on older gigabit links and all eight on newer ones. PoE puts a DC voltage, around 48 to 54 volts, onto pairs of those wires at the switch end. The camera has a circuit that takes that voltage off and uses it as its power supply.
Before the switch sends any power, it checks that the device at the other end wants it. A laptop plugged into a PoE port gets data only. A camera gets data and power. That negotiation is why PoE is safe to mix with ordinary devices on the same switch.
The switch doing the powering is called the PSE (power sourcing equipment). The camera is the PD (powered device). Those two terms turn up on every datasheet.
PoE, PoE+ and PoE++
There are three standards, and the difference is how much power each port can deliver.
| Standard | IEEE name | Power at the switch port | Power at the device after cable loss | Typical use |
|---|---|---|---|---|
| PoE | 802.3af | 15.4 W | 12.95 W | Fixed dome and bullet cameras, VoIP phones, small access points |
| PoE+ | 802.3at | 30 W | 25.5 W | Cameras with heaters or strong IR, PTZ cameras with lighter motors, Wi-Fi 6 access points |
| PoE++ | 802.3bt | 60 W or 90 W | 51 W or 71 W | Outdoor PTZ with heater and wiper, LED signage, thin clients |
A PoE+ switch will power a PoE device. A PoE switch will not power a PoE+ device fully; the camera may boot, then drop out when the IR lights or heater switch on. That’s the most common "camera goes offline at night" fault we hear about.
Check the camera datasheet for its maximum consumption and the standard it needs. A Dahua fixed IP camera is usually under 7 W. A full-size outdoor PTZ can be 60 W or more and needs PoE++ or its own 24 V supply.
The power budget
Every PoE switch has two numbers that matter: the power per port and the total power budget for the whole switch. The second one is the trap.
An 8-port PoE+ switch can give 30 W on any single port. It doesn’t follow that it can give 30 W on all eight at once. The total budget might be 120 W, which is 15 W per port if every port is loaded. Fill it with eight cameras drawing 18 W each and the switch will start refusing power to the last ones that connect, or shedding ports when the total goes over.
The sizing is simple arithmetic.
Add up the maximum power draw of every device that will hang off the switch. Use the datasheet maximum, not the typical figure, because the maximum is what the camera pulls when IR and heater are on at the same time. Add 20 percent for cable losses on long runs and for headroom. That’s the minimum budget the switch needs.
Worked example for a small warehouse: twelve fixed bullet cameras at 6.5 W, two turret cameras with active deterrence at 12 W, one PTZ at 25 W.
Twelve times 6.5 is 78 W. Two times 12 is 24 W. One PTZ is 25 W. Total 127 W. Add 20 percent and you need a switch with at least 155 W of PoE budget across 15 ports. A 16-port switch with a 250 W budget covers it with room for the two cameras the client will add next year. A 16-port switch with a 130 W budget looks fine on the port count and will fail in summer.
Managed or unmanaged
An unmanaged PoE switch is plug and play. Cameras in, uplink to the recorder, done. For a single-switch site with cameras only, that’s enough.
A managed switch lets you log in and configure it. For a camera network that matters in three cases: VLANs to separate camera traffic from the office network, per-port power control so a frozen camera can be rebooted remotely by cycling its PoE, and monitoring so you can see which port is drawing what. On any site with more than one switch or a shared network, managed is the right call and the price gap is small.
Ruijie’s Reyee range, which we carry, covers both. The PoE switch range lists the port counts and budgets.
Distance
PoE and data both run 100 m on copper. That’s the standard limit for one Ethernet segment, cable included, and it applies whether or not power is involved.
For a camera 180 m away, you have three options. Put a PoE switch somewhere in the middle. Use a PoE extender, which is a small powered repeater that adds another 100 m. Or run fibre to a small switch near the camera and power the camera locally. Some Dahua cameras and Ruijie switches also support an extended-range PoE mode that stretches to 250 m at lower speed, which is fine for a camera stream.
What you can’t do is run 180 m of Cat6 and hope. The camera may link but drop packets, and the power loss over that length will starve it.
Cabling that makes PoE fail
Copper-clad aluminium cable. It’s cheaper, it’s sold as Cat6, and its resistance is much higher than solid copper. Power loss over 60 m is enough to drop a PoE+ camera. Specify solid copper and reject CCA on delivery.
Long runs of thin cable. Cat5e works for PoE, but Cat6 with its thicker conductors loses less power over distance. On runs past 70 m, use Cat6.
Unterminated or badly crimped ends. A single bad pair can carry data but not power on some switches.
Cable bundles in hot roof voids. PoE cable warms up under load. Thirty cables bundled in a 50 degree ceiling space derate the power they can carry. Spread them or use conduit with airflow.
PoE from the recorder or from a switch
Most Dahua NVRs come with built-in PoE ports, 4, 8 or 16. For a small site, that’s the switch; the cameras plug into the back of the recorder.
Those ports have a total PoE budget too, and it’s often lower than a dedicated switch. An 8-port PoE NVR may carry 80 W to 100 W total. Check it against the camera list exactly as you would a switch.
For anything past 16 cameras, for PTZs, or for cameras spread across a building, use a dedicated PoE switch and uplink it to the recorder. The NVR vs DVR guide covers how the recorder side fits together.
PoE switches and IP cameras for projects in Oman
Elite Infotech supplies Ruijie PoE switches alongside Dahua IP cameras and recorders to system integrators across Oman, with stock in Muscat, Ruwi, Sohar and Salalah.
Call +968 9690 9419 or see the Ruijie PoE switch range.