Plug the wrong device into the wrong PoE port and you either get nothing, or you get a dead radio. Here is what actually separates 48 V active PoE from 24 V passive PoE, and how to tell which one your gear needs.
Both put DC power down the same Ethernet cable as your data. The difference is whether anything checks the device before the power turns on.
48 V active PoE (IEEE 802.3af/at/bt). Almost every modern IP camera, Wi-Fi access point, IP intercom and VoIP phone expects it, whatever the brand.
Older outdoor radios and point-to-point links, plus some solar or battery sites that run straight off a 24 V bank. It is not a standard, so it only works with matching gear.
Not safely. At best the device won’t power up. At worst, 24 V goes into a port that was never designed for it. Use a converter, or a switch that supports both.
Active PoE has a short conversation with the device first. Passive PoE just sends 24 V down the cable and hopes the right thing is on the other end.
An active switch is a careful electrician. A passive injector is a live wire with a plug on it.
| 48 V active PoE | 24 V passive PoE | |
|---|---|---|
| Voltage | 44–57 V (nominally 48 V) | Fixed, about 24 V |
| Safety check | Detects and classifies the device before powering it | None. The cable is always live |
| Power per port | 15.4 W (af), 30 W (at), 60–90 W (bt) | Usually 12–24 W, depending on the injector |
| Cable reach | 100 m on Cat5e or better | Shorter under load, because voltage drop bites much sooner |
| Compatibility | Any brand that follows the IEEE standard | Only the matching vendor’s gear and pin-out |
| Typical gear | IP cameras, access points, IP intercoms, VoIP phones | Legacy outdoor radios and CPEs, some solar sites |
Each newer standard is backward compatible, so a PoE+ switch will happily power an older 802.3af camera. The figure that matters is what reaches the device.
The big number on each card is the power guaranteed at the device. The switch sends a little more, because some is always lost as heat in the cable.
For the same wattage, halving the voltage doubles the current. Cable loss rises with the square of the current, so 24 V wastes far more power in the same cable.
That is why passive links often work fine on the bench, then reboot at random once the radio is on a pole 80 m away and its heater kicks in on a cold morning.
Push a 24 V link much past 15 W over 100 m and no amount of regulation will save it: the cable simply can’t deliver it. The same cable at 48 V can carry about four times as much.
Avoid copper-clad aluminium (CCA) cable for any PoE. Its higher resistance makes every number here worse.
This is where most problems come from. Check this before you plug anything in.
| Power source | Device | What happens |
|---|---|---|
| 48 V active switch | 802.3af/at device | WorksExactly as designed. |
| 48 V active switch | 24 V passive device | No powerThe switch finds no signature and leaves the port off. Safe, but it won’t run. Use an 802.3af-to-24 V converter such as the Ubiquiti INS-3AF-I-G, or a switch with a 24 V mode. |
| 24 V passive injector | 802.3af/at device | Won’t startThe voltage is too low for a standard device. It may not boot, or may boot-loop. |
| 24 V passive port | Non-PoE device laptop, router, NVR | Risk of damage24 V goes straight into an Ethernet port that was never built for it. |
| 48 V passive injector | 24 V passive device | Likely destroyedDouble the rated voltage, with nothing to stop it. |
Label every passive port. Put a sticker on each 24 V injector and switch port, and on the cable at both ends. Passive brands also use different pin-outs, so check the manual before mixing vendors.
Most current outdoor radios now accept standard 802.3af/at. When legacy gear reaches end of life, standardise on active PoE.
Including one switch that can still feed 24 V passive devices while you migrate.
Runs bothFour PoE ports that can output standard PoE or 24 V passive. One switch for new and legacy gear while you migrate.
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Safe default802.3af/at on all eight ports. The everyday choice for cameras, access points and intercoms.
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Single runAdds standard 802.3at power to one cable when your existing switch has no PoE.
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Solar & batteryRuns straight off a 12–48 V battery or solar bank and outputs standard PoE+.
View product →Browse all network switches or PoE injectors and adaptors. Wiring up an IP intercom? Read What is SIP?
PoE+ is 802.3at, one of the 48 V active standards. It runs at 50–57 V and delivers up to 30 W per port. Plain “PoE” (802.3af) delivers up to 15.4 W.
No. An 802.3af/at/bt switch only sends power after it detects a PoE device, so laptops, routers and NVRs on the same switch are safe. Passive PoE gives you no such protection.
Check the datasheet or the label near the Ethernet port. “802.3af”, “802.3at”, “PoE+” or “PoE++” means active. “24V passive”, or a bundled injector marked 24 V, means passive.
Yes. An 802.3af-to-24 V passive converter lets a standard switch power a legacy passive device. Going the other way, a PoE switch with a DC input can run standard devices from a battery or solar supply.
A little. Cat6 conductors are usually slightly thicker, so they lose less power and run cooler in large bundles. The bigger win is using solid pure-copper cable rather than copper-clad aluminium.
Send us the model numbers and we’ll tell you which switch or injector will run it safely.
Information is provided in good faith and may change. Always confirm voltage, power and pin-out requirements with the device manufacturer before connecting power.
