How much power does a PoE switch need per port?

Q: How far can I run Cat 6 for PoE?

PoE distance is bounded by the same 100 m Ethernet channel, but power delivery also depends on resistive loss over that run. This calculator estimates I²R loss from the conductor gauge and length, then adds it to the device draw to find the PSE port power. Longer runs and thinner conductors raise loss, so 4-pair 802.3bt at 23 or 22 AWG carries high-wattage loads farther than 2-pair 802.3af on 24 AWG.

Q: Why does 802.3bt deliver more power than 802.3af?

IEEE 802.3af and 802.3at carry power on 2 pairs, while 802.3bt Type 3 and Type 4 parallel all 4 pairs, halving the loop resistance and cutting cable loss. This calculator models that by computing loop resistance as ρ×L for 2-pair types and ρ×L/2 for 4-pair types. Lower loss plus higher PSE limits is why Type 4 reaches 90 W per port.

Question

How much power does a PoE switch need per port?

Accepted Answer

The PSE port must source the device draw plus the resistive cable loss, so per-port PSE power equals PD watts plus I²R loss in the channel. IEEE 802.3af allows up to 15.4 W per port, 802.3at up to 30 W, and 802.3bt Type 3 and Type 4 up to 60 W and 90 W. The tool also confirms the device draw stays within each standard's PD class maximum.

How much power does a PoE switch need per port?

Answers