CompTIA Network+ (N10-009)Network TroubleshootingMedium
A company recently added several new VoIP phones and Wi-Fi access points to a PoE switch that already powers existing devices. Shortly afterward, some devices begin randomly losing power and rebooting, especially during peak usage. Cable testing shows no faults. What is the most likely cause?
- AA VLAN misconfiguration on the new ports
- BThe switch's total PoE power budget has been exceeded
- CFaulty Cat 6 cabling to the new devices
- DDuplex mismatch on the switch ports
Show answer & explanationAnswer & explanation
Correct answer: B. The switch's total PoE power budget has been exceeded
PoE switches have a finite total power budget shared among all connected powered devices (PDs). Adding more PoE devices can exceed this budget, causing the switch to cut power to some ports, especially under peak load. Cable testing already ruled out physical faults.
Why the other options are wrong
- A. VLAN misconfiguration affects traffic segmentation, not power delivery.
- C. Cable testing already confirmed the cabling is fine.
- D. Duplex mismatch causes performance degradation, not power loss.
PoE Power Budget
The total wattage a PoE switch can supply across all its ports; exceeding it causes the switch to shed power from some ports.
- Each PoE switch has a maximum total power budget (e.g., 370W).
- Adding high-draw devices like PoE+ APs or phones can exceed the budget.
- Symptoms include random device reboots or power loss under load.
Memory trick: 'Too many mouths, not enough power pie.'