[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"article-poe-power-classes-0-8-explained":3},{"id":4,"slug":5,"title":6,"category":7,"summary":8,"tags":9,"publishTime":15,"views":16,"seoTitle":17,"seoDescription":18,"seoKeywords":19,"content":20},14,"poe-power-classes-0-8-explained","PoE Power Classes 0 to 8 Explained","standards","What each PoE class means at the PSE and at the PD, how physical-layer classification works, and why LLDP negotiation and Autoclass change your power budget.",[10,11,12,13,14],"PoE class","classification","LLDP","power budget","PSE","2026-07-05",12,"PoE Power Classes 0-8 Explained: PSE and PD Power Levels","A complete PoE class reference: classes 0 through 8, PSE and PD power for each, how 1-event, 2-event and multi-event classification work, and when LLDP takes over.","PoE class, PoE classes 0-8, class 4 PoE, class 8 PoE, PoE classification, LLDP power negotiation, PSE PD power, Autoclass","\u003Cp>Every standardized PoE link begins with a negotiation in which the powered device tells the power sourcing equipment how much power it needs. That negotiation resolves to a class number between 0 and 8. The class determines how much power the PSE reserves from its budget, which in turn determines how many devices a switch can actually run. Understanding classes is the difference between a power budget that works on paper and one that works in the rack.\u003C\u002Fp>\u003Cimg src=\"\u002Fbrand\u002Fnet\u002Fethernet-switch.jpg\" alt=\"managed ethernet switch ports\" loading=\"lazy\" \u002F>\n\u003Ch2>Detection Comes First\u003C\u002Fh2>\n\u003Cp>Before classification, the PSE must confirm that something safe to power is attached. It applies a low probing voltage, typically between 2.8 V and 10 V, and looks for the characteristic 25 kΩ signature resistance that every compliant PD presents. Only when a valid signature is found does the PSE proceed. This step is why you can safely plug a laptop or a non-PoE printer into a PoE port: without the signature, no operating voltage is ever applied.\u003C\u002Fp>\n\u003Ch2>The Class Table\u003C\u002Fh2>\n\u003Cp>Classification happens next, in the 15.5 V to 20.5 V window. The PD draws a specific current and the PSE reads that current as a class. The PSE-side figure is what the switch subtracts from its budget; the PD-side figure is what the device is guaranteed to receive at the far end of a worst-case 100 m channel.\u003C\u002Fp>\n\u003Ctable>\u003Cthead>\u003Ctr>\u003Cth>Class\u003C\u002Fth>\u003Cth>PSE reserves\u003C\u002Fth>\u003Cth>Guaranteed at PD\u003C\u002Fth>\u003Cth>Type\u003C\u002Fth>\u003Cth>Typical devices\u003C\u002Fth>\u003C\u002Ftr>\u003C\u002Fthead>\u003Ctbody>\n\u003Ctr>\u003Ctd>0\u003C\u002Ftd>\u003Ctd>15.4 W\u003C\u002Ftd>\u003Ctd>0.44-12.95 W\u003C\u002Ftd>\u003Ctd>1\u003C\u002Ftd>\u003Ctd>Legacy and unclassified PDs\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>1\u003C\u002Ftd>\u003Ctd>4.0 W\u003C\u002Ftd>\u003Ctd>3.84 W\u003C\u002Ftd>\u003Ctd>1\u003C\u002Ftd>\u003Ctd>VoIP handsets, sensors\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>2\u003C\u002Ftd>\u003Ctd>7.0 W\u003C\u002Ftd>\u003Ctd>6.49 W\u003C\u002Ftd>\u003Ctd>1\u003C\u002Ftd>\u003Ctd>Fixed IP cameras, simple APs\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>3\u003C\u002Ftd>\u003Ctd>15.4 W\u003C\u002Ftd>\u003Ctd>12.95 W\u003C\u002Ftd>\u003Ctd>1\u003C\u002Ftd>\u003Ctd>Dome cameras, single-radio APs\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>4\u003C\u002Ftd>\u003Ctd>30 W\u003C\u002Ftd>\u003Ctd>25.5 W\u003C\u002Ftd>\u003Ctd>2\u003C\u002Ftd>\u003Ctd>Wi-Fi 6 APs, cameras with heaters\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>5\u003C\u002Ftd>\u003Ctd>45 W\u003C\u002Ftd>\u003Ctd>40 W\u003C\u002Ftd>\u003Ctd>3\u003C\u002Ftd>\u003Ctd>Multi-radio APs, small displays\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>6\u003C\u002Ftd>\u003Ctd>60 W\u003C\u002Ftd>\u003Ctd>51 W\u003C\u002Ftd>\u003Ctd>3\u003C\u002Ftd>\u003Ctd>PTZ cameras, thin clients\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>7\u003C\u002Ftd>\u003Ctd>75 W\u003C\u002Ftd>\u003Ctd>62 W\u003C\u002Ftd>\u003Ctd>4\u003C\u002Ftd>\u003Ctd>PoE lighting, video bars\u003C\u002Ftd>\u003C\u002Ftr>\n\u003Ctr>\u003Ctd>8\u003C\u002Ftd>\u003Ctd>90 W\u003C\u002Ftd>\u003Ctd>71.3 W\u003C\u002Ftd>\u003Ctd>4\u003C\u002Ftd>\u003Ctd>Laptops, digital signage\u003C\u002Ftd>\u003C\u002Ftr>\n\u003C\u002Ftbody>\u003C\u002Ftable>\n\u003Ch2>Class 0 and the Cost of Not Classifying\u003C\u002Fh2>\n\u003Cp>Class 0 is the default a PSE assigns when a device presents a valid detection signature but no meaningful classification current. The PSE has no information, so it assumes the worst and reserves the full 15.4 W. A rack full of class 0 devices that each draw 4 W will exhaust a switch's budget at roughly a quarter of its real capacity. If you are designing a PD, implementing proper classification costs almost nothing and pays for itself the first time a customer fills a switch.\u003C\u002Fp>\n\u003Ch2>One Event, Two Events, Many Events\u003C\u002Fh2>\n\u003Cp>802.3af used a single classification event. 802.3at introduced 2-event classification: the PSE repeats the classification pulse, and a Type 2 PD that observes the second event knows it is attached to a PSE capable of 30 W, while a Type 1 PD simply ignores the repetition. 802.3bt extends this with longer sequences that let the PSE and PD converge on classes 5 through 8 and establish whether the PD is single- or dual-signature. The mechanism is deliberately layered so each generation degrades gracefully against older equipment.\u003C\u002Fp>\n\u003Ch2>When LLDP Takes Over\u003C\u002Fh2>\n\u003Cp>Physical-layer classification is coarse. Link Layer Discovery Protocol power negotiation runs at layer 2 once the link is up and lets the PD request a precise wattage in 0.1 W steps, then renegotiate as its needs change. An access point can boot conservatively, bring up its radios, and ask for more only if a second radio is enabled. The catch is timing: LLDP cannot run until the link is established, so the PD must survive on its physical-layer allocation long enough to get there. A device that requests class 4 and then negotiates 19.5 W over LLDP returns 10.5 W to the switch budget, but only where LLDP power management is enabled - on many switches it is off by default.\u003C\u002Fp>\n\u003Ch2>Budgeting With Classes\u003C\u002Fh2>\n\u003Cp>To size a switch, add the PSE-side reservation for every port you intend to populate, not the PD-side figure and not the measured draw. Then compare that total with the switch's system power budget, which is almost always lower than the sum of its per-port maximums. A 24-port switch rated class 4 on every port would need 720 W of PoE budget to deliver on that promise; most 24-port models ship with 370 W to 400 W, which is ample for a realistic mix but not for twenty-four simultaneous 30 W loads. Where the mix is uncertain, Autoclass or LLDP is what turns a theoretical shortfall into a working installation.\u003C\u002Fp>"]