UK What a PoE switch does
A PoE switch is an Ethernet switch with Power over Ethernet built into some or all of its ports. Like any switch, it forwards data between the devices plugged into it. On top of that, each PoE port can inject DC power onto the same twisted-pair cable, so a camera, access point or sensor runs from one cable with no mains socket or power supply at the device.
In PoE terms the switch is the power sourcing equipment (PSE) and the device it powers is the powered device (PD). Ports on a PoE switch follow one of the IEEE 802.3 standards: 802.3af (PoE, about 15 W), 802.3at (PoE+, about 30 W) or 802.3bt (PoE++, 60 W or 90 W). Our guide to what PoE is covers the technology itself.
Every PoE switch has two limits that matter: the maximum power per port, set by the standard it supports, and a total power budget shared across all its ports. Choosing one means checking both against the devices you plan to connect.
How a PoE switch powers a device
A standards-based PoE switch never sends full power down a cable blindly. Each port goes through a short sequence when something is plugged in.
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Detection. The port applies a low voltage, between about 2.7 and 10 V, and looks for the 25 kΩ signature resistor a PoE device presents. A laptop or printer without that signature gets data only, never power.
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Classification. The device signals its power class, so the switch knows how much to reserve for that port. PoE+ and PoE++ devices can refine this later over LLDP.
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Power on. The switch applies around 48 V DC, typically 44 to 57 V depending on the standard, and keeps monitoring the current. If the device is unplugged or draws too much, the port shuts off.
PoE budget and port limits
The PoE budget is the total wattage the switch’s power supply can share across its PoE ports. An 8-port PoE+ switch with a 120 W budget can run four 30 W devices at full power, or eight devices that draw 15 W each, but not eight at 30 W. Add up what each device draws at its worst case, such as a camera with IR and heaters on at night, then leave around 20 to 30% headroom. Budgets are often smaller than ports multiplied by the per-port maximum, so a 16-port PoE+ switch may have a 300 W budget rather than 480 W. Devices that draw a surge at start-up, such as PTZ motors or heaters, also need margin. Our PoE power budgeting guide works through a full example.
| Option | What it does | Best for | Limits |
|---|---|---|---|
| Unmanaged PoE switch | Powers and switches, no settings | Small fixed camera or sensor groups | No per-port control or monitoring |
| Managed PoE switch | Adds per-port power control, VLANs and monitoring | Sites that need remote reboot, scheduling and segmentation | Needs configuring |
| PoE injector | Adds power to one cable from a normal switch | One or two PoE devices | One more box and power point per device |
| PoE computer | Edge computer with built-in PoE ports | Cameras feeding local processing | Fewer ports than a switch |
Managed vs unmanaged PoE switches
An unmanaged PoE switch is plug-and-play: it detects, classifies and powers devices automatically, but you cannot see or change anything. A managed PoE switch adds control over each port. You can see how many watts each device is drawing, set port priorities so critical devices keep power if the budget runs short, schedule power off overnight, and power-cycle a frozen camera from a remote site. Many managed models also run a watchdog that pings each device and restarts its port if it stops answering. Our explainer on managed switches covers VLANs, QoS and redundancy.
What industrial PoE switches add
Office PoE switches assume a clean, cooled room and an AC socket. Industrial versions are built for cabinets, trackside enclosures and vehicles. Typical features are fanless metal housings for DIN-rail or panel mounting, wide operating temperatures such as −40 to 75 °C, dual redundant DC power inputs, and a wide DC input range with a boost converter so a 12 or 24 V supply can still deliver 48 V PoE. Some add M12 connectors for vibration, ring redundancy for fast failover, and 802.3bt ports for heated outdoor cameras. Our industrial PoE switches cover managed and unmanaged builds from 4 to 24 PoE ports, many with SFP fibre uplinks for runs beyond 100 m back to the control room, and our guide to PoE in surveillance and NVR systems shows how they fit a camera network.
Quick answers on PoE switches
PoE switches: common questions
What is the difference between a PoE switch and a regular switch?
Power on the ports. Both forward data the same way. A PoE switch also supplies DC power over the cable to devices that request it, and has a larger power supply to do so.
Can a PoE switch damage a non-PoE device?
Not a standards-based one. An 802.3af, at or bt switch only powers a port after detecting a PoE signature, so laptops and printers receive data only. Passive PoE equipment does not check, so it can.
What is a managed PoE switch?
A PoE switch you can configure. It adds per-port power monitoring, priorities, scheduling and remote power-cycling, plus normal managed features such as VLANs and QoS.
Do PoE switches need special cable?
No. Standard Cat5e or better carries PoE up to 100 m. For 90 W PoE++, all four pairs must be wired, and Cat6 or Cat6A runs cooler in large bundles.
Do I need a PoE switch for PoE cameras?
You need a PoE source, not necessarily a switch. A PoE switch, an NVR with PoE ports, a PoE computer or an injector will all power a PoE camera.
We supply industrial PoE switches and PoE computers sized to the site’s device list and power budget, integrated with the rest of the system as standard. Send us your device list and power input, and we will specify the ports and budget to match.