PoE Power Budget Calculator (Watts)
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.
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