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NETWORKING · POWER

PoE Mode A vs Mode B: What Is the Difference?

PoE Mode A (endspan) carries power on the data pairs, pins 1, 2, 3 and 6; Mode B (midspan) uses the spare pairs, 4, 5, 7 and 8. IEEE-compliant powered devices must accept either, and 802.3bt uses all four pairs.

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The Short Answer

Mode A and Mode B describe which pairs in the cable carry the power. Mode A (endspan) puts power on the same pairs as the data; Mode B (midspan) uses the two spare pairs. The data is unaffected either way, and a compliant device must accept power on either set.

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    Mode A (endspan) Power on pins 1, 2, 3, 6, shared with data.
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    Mode B (midspan) Power on pins 4, 5, 7, 8, the spare pairs.
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    PD requirement IEEE 802.3af/at/bt devices accept either mode.
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    802.3bt Uses all four pairs together for the highest power.