PoE Splitter: One Cable, Two Outputs
Quick answer / TL;DR: Short answer: choose an active PoE splitter that negotiates 802.3af or at, and set its output voltage to match the device. Passive splitters apply voltage without negotiation and can damage non-PoE equipment, so use them only where both ends are known to be compatible. Check the device's current draw against the splitter's rating, and remember that the splitter consumes a few watts itself. For 802.3bt devices, use a bt-rated splitter.
Three PoE adapters: injector adds power, splitter removes it, midspan sits in the run.A PoE splitter takes a powered Ethernet connection and separates it into a data connection and a DC output. It lets a device that has no PoE support, such as a small router, a non-PoE camera or a thin client, be powered from the same cable that carries its network link.
The splitter negotiates with the switch or injector, then converts the PoE voltage to whatever the device expects. Both halves of that sentence matter: a splitter that does not negotiate can damage equipment, and one that outputs the wrong voltage will not run the device.
What It Does
The splitter presents a valid powered-device signature to the switch or injector, receives power, and outputs DC on a barrel jack or terminal while passing the data through on an RJ45.
| Standard | Max at source | Max at device | Splitter output options |
|---|
| 802.3af | 15.4 W | 12.95 W | 5 V, 9 V, 12 V | 802.3at | 30 W | 25.5 W | 12 V, 19 V, 24 V | 802.3bt Type 3 | 60 W | 51 W | 12 V to 24 V | 802.3bt Type 4 | 90 W | 71 W | higher voltages |
The voltage options exist because devices differ. A small router may want 12 V, a thin client 19 V, and a camera 5 V, and the splitter has to be set to the right one before connection.
Active and Passive
The distinction is not marketing. An active splitter implements the detection and classification handshake; a passive one simply passes whatever voltage appears on the cable.
- Active: negotiates, safe with standard PoE equipment, preferred
- Passive: no negotiation, used in some proprietary systems including passive 24 V injectors
- Passive splitters can destroy non-PoE equipment if the source is a standard switch
- Check which type the whole system expects before mixing parts
- Confirm the splitter's own consumption, typically 1 to 3 W
Real-World Applications
Non-PoE camera on a PoE switch
A camera with a 12 V barrel jack and no PoE support can run from a splitter at the camera end, using one cable for both power and data. This is the most common use.
Small access point or router in a ceiling
Devices that expect a wall adapter can be relocated to where only a network cable reaches. Confirm the voltage and the current draw before setting the splitter.
Digital signage player
A player at 12 V or 19 V can be powered over the network cable, avoiding a local mains outlet. Check the total power budget on the switch port, because a bt port shared with other loads may not deliver what is needed.
Where a splitter is a poor choice
High-power devices above the splitter's rating, and any situation where the switch has a limited power budget. Adding a splitter increases the load on that budget rather than creating capacity.
Related reading: PoE classes compared — blogs/news/poe-af-at-bt
Related reading: Cable selection for PoE — blogs/news/poe-cable
Standards and Verification
PoE is defined in IEEE 802.3, with 802.3af for Type 1, 802.3at for Type 2 and 802.3bt for Types 3 and 4. The standard defines detection, classification and the power available at source and device, which is why active splitters interoperate without configuration.
Verify by checking the power class the switch reports for that port and confirming the device runs under full load without resetting. A device that boots and then cycles is drawing more than the splitter or the class provides.
Measure the DC output before connecting an expensive device. A splitter set to the wrong voltage is indistinguishable from a faulty device until the output is checked.
Label the voltage setting on the splitter permanently. The switch is small and easily disturbed, and a device rated for 12 V connected to a 19 V output will fail immediately.
Frequently Asked Questions
What does a PoE splitter do?
It separates a powered Ethernet connection into data and DC power, letting a non-PoE device run from one cable.
What is the difference between active and passive splitters?
Active splitters negotiate PoE properly and are safe with standard equipment. Passive ones pass voltage without negotiation and can damage devices.
How do I choose the output voltage?
Match the device's rating exactly, typically 5, 12, 19 or 24 V. Check before connecting.
Can I power a 12 V camera from a PoE switch?
Yes, with an active splitter set to 12 V, provided the camera's current draw is within the splitter's rating.
Does the splitter reduce available power?
It consumes a few watts itself, so the device receives slightly less than the port provides.
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