Intro lesson
Why Won’t My Access Point or Camera Power Up?
Understand Power over Ethernet, check the right limits and work through a simple power-budget example.
Reviewed September 2026 · 3 minute read
One cable can carry data and power
Power over Ethernet (PoE) supplies power over compatible network cabling. The switch or injector supplies it; the access point, camera or phone receives it. A port can support data without supplying PoE.
Compatibility
Match the device’s required PoE type with the exact switch port or injector. A connector that fits is not enough.
One port
Each port has its own power limit. A large switch budget cannot make an unsuitable port power a demanding device.
Whole switch
The total PoE budget is shared. Empty sockets do not necessarily mean spare watts.
IEEE PoE types and passive power products are different. Do not try an unidentified injector on equipment. Confirm the required voltage, power method and manufacturer compatibility first.
Four APs and two cameras
Worked example
A 120 W switch budget
| Planned allocation at the switch | Quantity | Total |
|---|---|---|
| AP allocation: 20 W each | 4 | 80 W |
| Camera allocation: 10 W each | 2 | 20 W |
| Total planned allocation | 6 devices | 100 W |
| Remaining budget | 120 − 100 | 20 W |
These are assumed switch-side allocations for practice, not specifications for named products. A new device needing 25 W at the switch would exceed the remaining budget. It also needs a compatible port.
For a real design, distinguish power supplied at the port from power delivered to the device, allow for cable loss and the switch’s allocation method, and plan headroom for startup, peak features and growth.
What to record before changing anything
- Record the device model, switch or injector model and port number.
- Check whether that specific port provides the required power type.
- Note power errors, recent additions and whether failure happens at startup or when a feature turns on.
- Have an authorized technician compare the cable, compatible source and device one item at a time.
A device that boots but cannot reach the network has passed a different milestone from one that stays completely dark. Treat those as separate symptoms.
Make the purchasing check
For one planned device, make a row with its required PoE type, maximum requirement, selected port, switch-side allocation and remaining budget. Mark any unknowns before ordering.
The switch has eight free ports but only 10 W left. Is another 20 W allocation okay?
No. Port count and power capacity are separate limits. Revise the power plan and verify the individual port and device requirements.
Put it into practice
Check what you learned
Choose an answer for each question, then check your understanding. Your answers stay in this browser.
Read the answers and explanations
- No; revise the power plan.
The stated allocation exceeds the remaining budget. Cable length does not change that arithmetic.
- Both the port compatibility and the total budget.
A suitable system must satisfy both limits.
- The models, port, power events, load changes and cable path.
Specific power and equipment information helps isolate the cause without guessing.
Sources and further reading
- Ubiquiti: PoE availability and modes
Shows why both the individual port and the switch power budget matter. Check your exact models.
Keep your momentum
Ready for the next step?
If you can explain the example and your answer, try the next lesson. Revisit the feedback whenever you need it.
FryAVSI · Updated September 10, 2026
Reference this lesson or use a section’s direct link for a particular chart or example. How to cite an example.
FryAVSI · Northeast Ohio and beyond
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