Quick answer: A PoE powered fiber converter draws its supply from the copper Ethernet port, so no mains outlet is needed at the far end. It needs a PoE injector or PoE switch on the copper side, a converter rated for the class it will receive, and a fiber pair to the rest of the network. Budget 4 to 13 W depending on the model and the copper device behind it.
Media converters used to require a mains socket and a small power brick at each end. That single requirement often decided the architecture, because the useful place for a converter is usually a ceiling, a pole or a cabinet with no power. PoE removes that constraint and adds a power budget you have to respect.
How the power path works
Power enters on the copper port as a common mode voltage, either on the spare pairs or superimposed on the data pairs. The converter extracts it, regulates it, and uses it for its own electronics and, on some models, for a downstream PoE passthrough port.
Which side has the injector
Put the injector or PoE switch on the copper side. The fiber side cannot carry power, so a converter fed from fiber would need a separate supply. In a typical link, the switch is indoors with mains power and the converter is outdoors or on a mast.
Class and wattage
802.3af provides up to 15.4 W at the source and about 12.95 W at the device. 802.3at provides 30 W and 25.5 W. A converter itself usually needs 3 to 6 W; the rest is only relevant if it passes power through to a camera or access point.
Power classes against converter types
| Converter type | Draw | PoE class needed | Typical use | Passthrough |
|---|
| 100M single fiber | 3 W | af | Legacy camera link | No |
| Gigabit duplex fiber | 4 W | af | Outdoor access point | No |
| Gigabit with PoE out | 5 W plus load | at | Camera on a mast | Yes, one port |
| 2.5G fiber converter | 6 W | at | Wi-Fi 6 access point | Sometimes |
| Industrial hardened | 7 W | at | Plant floor cabinet | No |
Designing the link so it survives a reboot
Negotiation order
The converter boots first, then brings up the copper link, then the fiber link. A PoE switch port that powers down when the link is lost can create a loop where the converter never finishes booting. Enable PoE power policing without link based shutdown, or use a dedicated injector.
Cable loss matters more than usual
PoE over 100 m of Cat5e loses several watts to resistance. The converter sees a lower voltage than the switch delivers, and a marginal class budget becomes a reboot loop under load. Use 23 AWG solid cable and keep the copper run under 80 m where possible.
Surge and grounding
An outdoor converter on a mast is a lightning target through both the fiber and the copper. Use a shielded enclosure, a properly bonded ground, and a fiber type that does not carry a metallic strength member to the equipment.
Temperature, enclosure and long term behaviour
A converter in a sealed outdoor box runs 15 to 20 C above ambient. The switching regulator inside is the hottest part, and its efficiency falls as temperature rises, which pushes current up and temperature higher. Choose a hardened model rated to 65 C rather than a commercial one rated to 50 C, and leave the box vented or shaded.
Practical scenarios
- Gate camera 180 m from the building: fiber from the switch to a PoE converter at the gate, injector indoors, single mode for the distance.
- Warehouse ceiling access point: PoE converter in a ceiling box, fiber back to the core, no mains feed in the ceiling void.
- Temporary event network: converter and injector in a flight case, multimode patch to the venue fiber, gigabit copper to the access point.
- Industrial cabinet: hardened converter on DIN rail, 802.3at from a PoE switch, fiber to the control room.
FAQ
Can I power the converter from the fiber side?
No. Fiber carries light only. Power always arrives on the copper port or from a local supply.
Does a PoE converter need a PoE switch?
It needs a PSE, which can be a PoE switch port or a single port injector. An injector is cheaper when only one link needs power.
What happens if the injector fails?
The converter loses power and the fiber link drops. For critical links, use a switch with dual power supplies rather than a single injector.
Next step
Size the power budget before the converter. Add up the converter draw and anything it passes through, then choose af or at. The fiber to RJ45 converter covers the data side of the same link, the PoE adapter buying guide explains injector selection, and the fiber connector types page confirms the polish and connector you need at each end.
