https://knightli.com/en/tags/poe-power/ Recent content in Poe-Power on KnightLi Blog Hugo -- gohugo.io en Sat, 28 Mar 2026 00:00:00 +0000 https://knightli.com/en/2026/03/28/ieee-802-3af-at-bt-poe-differences/ Sat, 28 Mar 2026 00:00:00 +0000 https://knightli.com/en/2026/03/28/ieee-802-3af-at-bt-poe-differences/ <p>IEEE 802.3af, 802.3at, and 802.3bt are the three mainstream PoE (Power over Ethernet) standards. Their key differences are power budget, number of wire pairs used for power delivery, and target device types.</p> <h2 id="quick-takeaways">Quick Takeaways </h2><ul> <li><code>802.3af (PoE)</code>: Lower maximum power (15.4W), suitable for basic devices.</li> <li><code>802.3at (PoE+)</code>: Increased power up to 30W, suitable for medium-power devices.</li> <li><code>802.3bt (PoE++ / 4PPoE)</code>: Highest power level (Type 3 up to 60W, Type 4 up to 90W-100W), suitable for high-power devices.</li> </ul> <h2 id="detailed-comparison">Detailed Comparison </h2><table> <thead> <tr> <th>Standard</th> <th>Common Name</th> <th>Max PSE Output</th> <th>Usable PD Power (Approx.)</th> <th>Powered Pairs</th> <th>Typical Use Cases</th> </tr> </thead> <tbody> <tr> <td>IEEE 802.3af</td> <td>PoE</td> <td>15.4W</td> <td>12.95W</td> <td>2 pairs</td> <td>Standard VoIP phones, basic cameras</td> </tr> <tr> <td>IEEE 802.3at</td> <td>PoE+</td> <td>30W</td> <td>25.5W</td> <td>2 pairs</td> <td>HD IP cameras, advanced network endpoints</td> </tr> <tr> <td>IEEE 802.3bt</td> <td>PoE++ / 4PPoE</td> <td>Type 3: 60W; Type 4: 90W-100W</td> <td>Higher (depends on type)</td> <td>4 pairs</td> <td>Wi-Fi 6/6E APs, video conferencing endpoints, building automation</td> </tr> </tbody> </table> <h2 id="standard-by-standard-notes">Standard-by-Standard Notes </h2><h3 id="ieee-8023af-poe">IEEE 802.3af (PoE) </h3><ul> <li>Max output power: 15.4W (about 12.95W available at PD)</li> <li>Pair usage: 2 out of 4 twisted pairs</li> <li>Typical scenarios: legacy cameras, standard VoIP phones</li> </ul> <h3 id="ieee-8023at-poe">IEEE 802.3at (PoE+) </h3><ul> <li>Max output power: 30W (about 25.5W available at PD)</li> <li>Pair usage: 2 out of 4 twisted pairs</li> <li>Typical scenarios: HD IP cameras, higher-end network surveillance endpoints</li> </ul> <h3 id="ieee-8023bt-poe--4ppoe">IEEE 802.3bt (PoE++ / 4PPoE) </h3><ul> <li>Max output power: up to 60W for Type 3, up to 90W-100W for Type 4</li> <li>Pair usage: all 4 pairs for power delivery, enabling higher power capacity</li> <li>Typical scenarios: high-power wireless APs, building automation, video conferencing systems</li> </ul> <h2 id="compatibility">Compatibility </h2><p>All three standards are backward compatible:</p> <ul> <li><code>802.3bt</code> is compatible with <code>802.3at</code> and <code>802.3af</code></li> <li><code>802.3at</code> is compatible with <code>802.3af</code></li> </ul> <p>As standards evolve, available power increases significantly, supporting a wider range of high-power terminal devices.</p>