Power over Ethernet (PoE) Power Standards Reference

The short answer

Power over Ethernet is defined by IEEE 802.3, and each revision sets two numbers that matter: the watts the Power Sourcing Equipment (PSE, usually a switch) puts onto the cable, and the smaller number the Powered Device (PD) is guaranteed to receive after loss over up to 100 meters. 802.3af (Type 1, "PoE") sources 15.4W and delivers about 12.95W to the PD. 802.3at (Type 2, "PoE+") sources 30W and delivers about 25.5W. 802.3bt Type 3 ("PoE++") sources 60W for roughly 51W at the PD, and Type 4 sources 90W for about 71.3W. All operate on 44-57V DC. Type 1 and Type 2 energize two of the four twisted pairs; 802.3bt Type 3 and Type 4 use all four pairs to carry more current at lower heat.

The gap between the source and device numbers is not marketing rounding: it is resistive (I²R) loss in the copper. A PSE guarantees its output, but the standard specifies what a PD must still see at the far end of a worst-case 100m channel, so the PD rating is deliberately lower. Devices announce their appetite through a classification handshake (a signature resistance plus a class current, refined by LLDP on Type 2 and later), which maps to power classes 0-8. To size a switch you add up the class draw of every connected device plus headroom, and check that figure against the switch's total power budget, which is almost always smaller than ports times per-port maximum. Below, each standard, class, cable, and device category is broken out with the real published figures.

Which PoE Type Powers Your Device

Start from the device, not the switch. Every PD carries a rating in watts, and the standard you need is the one whose PD-side delivery meets or exceeds that draw with a little margin. A single-band IP phone or a fixed-lens indoor camera typically draws under 13W, so 802.3af (Type 1, 12.95W at the PD) is sufficient. A Wi-Fi 6 access point, a pan-tilt-zoom (PTZ) camera, or a camera with an integrated heater usually lands between 15W and 25W, which is 802.3at (Type 2, 25.5W at the PD) territory. Multi-radio Wi-Fi 6E/7 access points, PTZ domes with heaters and blowers, and PoE LED lighting can exceed 30W and require 802.3bt Type 3 (51W) or Type 4 (71.3W).

Two mistakes cause most field problems. First, reading the PSE number instead of the PD number: a "30W" switch port delivers 25.5W to the device, so a 26W PD is out of spec on Type 2. Second, ignoring the switch's total budget. A port that can each supply 30W does not mean every port can at once; the shared power supply caps the sum. When a device's nameplate says "802.3at/bt" or lists a class, match that exactly. When it only lists watts, pick the first type whose PD delivery clears the draw, then confirm the switch budget covers all ports together.

• Under ~13W (VoIP phones, fixed IP cameras, sensors): 802.3af Type 1 delivers 12.95W at the PD.
• ~13-25W (Wi-Fi 5/6 APs, PTZ without heater, video doorbells): 802.3at Type 2 delivers 25.5W at the PD.
• ~25-51W (Wi-Fi 6E/7 APs, heated PTZ, thin clients): 802.3bt Type 3 delivers 51W at the PD.
• ~51-71W (multi-radio APs, PoE lighting, small displays, kiosks): 802.3bt Type 4 delivers 71.3W at the PD.
• Always compare the device draw to the PD (device-side) figure, never the PSE (switch-side) figure.
• Confirm the switch's total power budget covers the sum of all connected PDs, not just one port.

The Four PoE Types, Side by Side

The four IEEE designations map to a common nickname and a fixed pair of wattage numbers. 802.3af, ratified in 2003, is Type 1 ("PoE"): the PSE sources 15.4W, the PD is guaranteed 12.95W, over two pairs. 802.3at, ratified in 2009, is Type 2 ("PoE+"): 30W at the PSE, 25.5W at the PD, still two pairs. 802.3bt, ratified in 2018, added Type 3 and Type 4 and moved to all four pairs. Type 3 ("PoE++" / "4PPoE") sources 60W for 51W at the PD; Type 4 sources 90W for 71.3W at the PD. 802.3bt also formalized 10GBASE-T PoE and downward compatibility, so a Type 4 PSE still powers a Type 1 phone.

Voltage is DC. Type 1 PSE output sits in the 44-57V window with the PD guaranteed at least ~37V after cable loss; Type 2, Type 3, and Type 4 PSEs operate at 50-57V, with PD minimums near 42.5V (Type 2) and ~41.1V (Type 4). Two-pair standards can place power on the data pairs (Alternative A) or the spare pairs (Alternative B); a PD must accept either and either polarity. Four-pair 802.3bt energizes all eight conductors, which is what unlocks the higher wattage without overheating any single pair.

• 802.3af (Type 1, PoE, 2003): 15.4W PSE / 12.95W PD, 2 pairs, PSE 44-57V, ~350mA per pair.
• 802.3at (Type 2, PoE+, 2009): 30W PSE / 25.5W PD, 2 pairs, PSE 50-57V, up to ~600mA per pair.
• 802.3bt Type 3 (PoE++, 2018): 60W PSE / 51W PD, 4 pairs, 50-57V, up to ~600mA per pair.
• 802.3bt Type 4 (2018): 90W PSE / 71.3W PD, 4 pairs, 50-57V, up to ~960mA per pair.
• Two-pair power uses Alternative A (data pairs 1-2/3-6) or Alternative B (spare pairs 4-5/7-8); PDs accept either.
• All types share detection and classification, so higher-type PSEs remain backward compatible with lower-type PDs.

Power Classes 0-8 and the Handshake

Before a PSE applies 50-plus volts, it verifies a real PD is attached and learns how much power to allocate. Detection: the PSE probes at a low voltage (about 2.7-10.1V) and looks for the PD's signature, a 25kΩ resistance. Classification: the PSE then measures a class current the PD presents, sorting it into a class that reserves the right power budget. Type 2 and later can refine this with a second classification event and with LLDP (Link Layer Discovery Protocol) data-link negotiation, so a switch and device can agree on an exact allocation rather than a coarse class.

The classes and their PD maximum power are fixed. Class 0 is the default/unspecified bucket (up to 12.95W, reserving 15.4W at the PSE). Class 1 is 3.84W, Class 2 is 6.49W, Class 3 is 13W - all served by Type 1 or Type 2 PSEs. Class 4 (25.5W) is the Type 2 ceiling. 802.3bt added Class 5 (40W) and Class 6 (51W) for Type 3, and Class 7 (62W) and Class 8 (71.3W) for Type 4. The PSE reserves more than the PD rating for each class (for example, 90W reserved for a Class 8 71.3W device) precisely to cover cable loss. Under-classing wastes capacity; over-classing risks a port shutting the device off.

• Class 0: PD up to 12.95W, PSE allocates 15.4W (default when no valid class is presented).
• Class 1: 3.84W PD / ~4.0W PSE. Class 2: 6.49W PD / ~7.0W PSE. Class 3: 13W PD / 15.4W PSE.
• Class 4: 25.5W PD / 30W PSE (802.3at Type 2 maximum).
• Class 5: 40W PD / 45W PSE. Class 6: 51W PD / 60W PSE (802.3bt Type 3).
• Class 7: 62W PD / 75W PSE. Class 8: 71.3W PD / 90W PSE (802.3bt Type 4).
• Detection uses a 25kΩ signature resistor; Type 2+ can negotiate a precise allocation over LLDP instead of a fixed class.

Why the PD Gets Less: Cable Loss and Heat

The device always receives less than the switch sends because copper has resistance, and current through resistance dissipates power as heat (P = I²R). ANSI/TIA-568 permits a 100m channel, and balanced twisted-pair has a specified maximum DC loop resistance per pair, so the standard sizes the PD's guaranteed voltage for the worst case: a long, warm, thin-gauge run. That is why 15.4W at the PSE becomes 12.95W at the PD - roughly 2.45W is budgeted as loss. Because loss scales with the square of current, pushing more amps down a pair heats it disproportionately. This is the core reason 802.3bt spreads Type 3 and Type 4 across all four pairs: halving the current in each conductor cuts that conductor's heating to about a quarter.

Bundling compounds the effect. Cables packed in a conduit or tray cannot shed heat as easily, so the center of a large bundle runs hotter, and higher temperature raises copper resistance, which raises loss further. TIA's TSB-184-A addresses this with guidance on bundle sizes and cable selection for high-power PoE. Practical mitigations: prefer Cat6/6A with larger 23AWG conductors over 24AWG Cat5e for Type 3/4 runs, keep bundles modest, respect the cable's temperature rating (commonly 60°C or 75°C), and avoid running full-length high-wattage circuits through hot, unventilated spaces. Solid-conductor cable and clean terminations also reduce contact resistance at the connector, a frequent hidden source of loss and heat.

• Loss is resistive (P = I²R): the PD figure is set for a worst-case 100m ANSI/TIA-568 channel, hence PD < PSE.
• 802.3af: ~2.45W is budgeted for cable loss (15.4W PSE to 12.95W PD).
• Four-pair 802.3bt halves per-conductor current versus two-pair, cutting each conductor's heating to roughly a quarter for the same power.
• TIA TSB-184-A gives bundle-size and cable guidance for high-power PoE heat rise.
• Prefer 23AWG (Cat6/6A) over 24AWG (Cat5e) for Type 3/4; larger copper means lower resistance and less heat.
• Respect the jacket temperature rating (often 60-75°C) and keep large bundles out of hot, unventilated runs.

Budgeting a PoE Switch

A PoE switch has two independent limits: a per-port maximum (the highest type/class any one port supports) and a total power budget (what the internal supply can deliver across all ports at once). The total is almost always less than ports multiplied by the per-port maximum. A common 8-port PoE+ switch might support 30W on any port but carry a shared budget near 120-130W - enough for four ports at full PoE+, not eight. Budget on the PSE side: sum the power each port must source (the class-reserved figure, not the PD figure), because that reserved wattage is what the supply must hold in reserve.

Build the calculation as a table: list each device, its class or negotiated draw, and the PSE-side allocation, then total them and add headroom - a common practice is planning to about 80% of the budget so simultaneous peaks do not trip protection. Account for worst-case coincident load: PTZ cameras spike when heaters and motors run together, and access points draw more under full radio and client load. Also confirm the switch actually implements the type you need; many "PoE+" switches are Type 2 only and will not power a Type 3/4 device. Finally, verify the number of ports that can hit the high power simultaneously, since some switches allocate high-wattage ports from a smaller sub-pool.

For a fast first pass on real device lists, the internal tool below tallies class draw against a switch budget so you can see headroom before ordering hardware.

• Per-port max and total budget are separate limits; the budget is usually far below ports times per-port max.
• Budget using the PSE-side (class-reserved) wattage, since that is what the power supply must hold available.
• Plan to roughly 80% of the total budget so coincident peaks (heaters, motors, full AP load) stay within protection limits.
• PTZ cameras and multi-radio APs can spike well above their idle draw; size for worst-case simultaneous load.
• Confirm the switch's actual type: many "PoE+" switches are Type 2 only and cannot power Type 3/4 (51-71W) devices.
• Estimate a project quickly with the /tools/poe-budget calculator before finalizing switch selection.

What Powers What: Cameras, APs, Phones, PTZ

Mapping common devices to types keeps designs honest. VoIP desk phones are typically Class 1-2 (3.84-6.49W), comfortably powered by 802.3af Type 1. Fixed indoor IP cameras with fixed or motorized lenses usually fall in Class 2-3 (6.49-13W), also Type 1, though models with strong infrared illuminators can climb into Type 2. Outdoor bullet and turret cameras with heaters, and most PTZ domes, land in Class 4 (25.5W) and need 802.3at Type 2; large PTZ units with heaters and wipers can require 802.3bt Type 3 (up to 51W). Read the datasheet's peak figure, not the idle figure, because the heater and motor draw appears only in cold or moving conditions.

Wireless access points have climbed with each Wi-Fi generation. Many Wi-Fi 5 (802.11ac) APs run within Type 1 or low Type 2. Wi-Fi 6 (802.11ax) APs commonly want the full 25.5W of Type 2, and an AP starved on Type 1 may disable a radio, a USB port, or a second Ethernet port rather than fail outright - a subtle symptom worth checking. Wi-Fi 6E and Wi-Fi 7 multi-radio APs increasingly specify 802.3bt Type 3, and some high-density models Type 4. Emerging PoE loads - LED luminaires, small signage displays, access-control controllers, and thin clients - are designed around Type 3/4 (51-71.3W). When a device lists a class or an IEEE type, follow it exactly; when it lists only watts, size to the first type whose PD delivery clears the peak.

Getting the standard, cable grade, and switch budget aligned across a full building is where a low-voltage installer earns their keep. If you are wiring cameras, access points, or PoE lighting across a Houston-area site - or troubleshooting devices that boot, then reset or drop a radio under load - a professional install verifies the whole chain end to end: PSE type and budget, cable gauge and length, terminations, and heat in the bundle. EVOTECH IT LLC handles that design and installation work; a short conversation about device counts and run lengths is usually enough to scope it.

• VoIP phones: Class 1-2 (3.84-6.49W), 802.3af Type 1 is sufficient.
• Fixed IP cameras: Class 2-3 (6.49-13W), Type 1; add Type 2 headroom for strong IR or motorized lenses.
• PTZ / heated outdoor cameras: Class 4 (25.5W) Type 2, up to Type 3 (51W) for heaters, wipers, and blowers - size to peak, not idle.
• Wi-Fi 6 APs: usually full Type 2 (25.5W); on Type 1 they may disable a radio or port instead of failing.
• Wi-Fi 6E/7 multi-radio APs: often 802.3bt Type 3 (51W), some Type 4 (71.3W).
• PoE lighting, displays, door controllers, thin clients: designed around 802.3bt Type 3/4 (51-71.3W).

Frequently asked questions