PoE Injector for Security Camera: Power Over Ethernet Without PoE Switch

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  The PoE power budget for the switch has been exceeded

  Why this is correct

  The PoE power budget for the switch has been exceeded is the correct explanation. A PoE switch has a finite total wattage it can deliver across all ports. When that budget is fully allocated to existing powered devices, any newly connected IP phone will not receive power, even though the port is administratively up and data link may be established. The phone appears 'not powered' because the switch cannot supply power to that port — no individual port failure, just exhausted capacity.

• ✗

  The patch cable is a crossover cable

  Why it's wrong here

  A crossover cable is not the cause because modern Ethernet interfaces use auto-MDI/X to automatically detect and correct for straight-through/crossover wiring, so link will come up regardless of the patch cable type. More importantly, PoE operates at the physical layer by injecting power onto the data pairs (or spare pairs), and this is unaffected by whether the conductors are crossed between the two ends. Since the switch can still perform PoE detection and power a device even with a crossover cable, this cannot explain a 'not powered' condition.

• ✗

  The IP phone requires a higher PoE standard than the switch supports

  Why it's wrong here

  If an IP phone requires a higher PoE standard than the switch provides (e.g., 802.3at PoE+ vs. 802.3af PoE), the switch would typically still detect the device via its PoE signature and attempt to classify it into a power class. If the requested power is beyond the port's capability, the switch would either supply the lower class power (which may cause the phone to fail to boot or to behave erratically) or mark the port as 'insufficient power'—but it would not simply show 'not powered.' Thus, this mismatch would produce a different diagnostic indication, not a complete absence of power.

• ✗

  The port is administratively disabled

  Why it's wrong here

  If a port is administratively disabled (shutdown), the correct status would be 'down' or 'disabled,' reflecting the Layer 2 interface state, not a PoE-specific status. On managed PoE switches, PoE configuration is independent of the port admin state; a port can be shut while still providing PoE power (if configured) or up but with PoE disabled. Therefore, an administrative shutdown would not present as 'not powered' in the PoE status; you would see a link-down condition instead.