Power over Ethernet (PoE) & Cabling Infrastructure Flashcards
7 cards from real CWT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Power over Ethernet (PoE) & Cabling Infrastructure flashcards as text
What is the maximum PSE power output per port defined by IEEE 802.3bt Type 4 (Class 8)?
Answer: 90 watts
IEEE 802.3bt Type 4 delivers up to 90W at the PSE using all four wire pairs, enabling high-power devices like multi-radio access points and PTZ cameras.
In IEEE 802.3af/at Alternative A power delivery mode, which wire pairs carry the power signal?
Answer: The data-carrying pairs (pins 1, 2, 3, 6)
Alternative A delivers power on the same pairs used for data transmission by superimposing a DC offset, while Alternative B uses the spare pairs.
What is the function of PoE PD power classification?
Answer: To allow a PD to signal its maximum power requirement to the PSE
PoE classification allows a PD to communicate its power class (0–8) to the PSE so the switch can allocate the correct wattage and manage its total power budget efficiently.
A wireless access point is PoE Class 3 under IEEE 802.3af. What is its maximum allowable power draw at the device?
Answer: 12.95 watts
Under IEEE 802.3af, a Class 3 PD can draw a maximum of 12.95W at the device after cable losses, making it the highest class under the original PoE standard.
What is the primary purpose of a PoE splitter?
Answer: To separate power from data so non-PoE devices can use PoE infrastructure
A PoE splitter separates the DC power from the data signal on an Ethernet cable, providing a standard data port and a separate DC power connector for non-PoE-capable devices.
Which physical factor most significantly causes power loss across a PoE cable run?
Answer: Conductor resistance of the cable
Conductor resistance causes power loss proportional to the square of the current (P = I²R), which is why wire gauge (AWG) and cable quality directly impact PoE efficiency.
What best practice should be followed when planning power budgets for a PoE switch in a wireless deployment?
Answer: Sum device power requirements by class and add 20–25% headroom
Summing per-device class power requirements and adding 20–25% headroom prevents power budget exhaustion, accommodating startup surges and future device additions.