Check whether one switch has enough total PoE capacity and ports, whether every port supports its device, how much power cable loss adds, and what voltage reaches each powered device. Plan class or LLDP allocation, simultaneous peak loads, and long cable runs in one place.
A 15–20% reserve is a planning starting point; increase it for uncertain peaks or future growth.
Actual draw estimates electrical load. Class mode reserves the negotiated PSE maximum. LLDP mode uses the editable per-port allocation.
Enter one or more device groups to estimate total source power and spare budget.
| Group | Qty | Per-port source W | PD voltage | Voltage drop | Loss per port | Total source W | Status |
|---|---|---|---|---|---|---|---|
| No calculation yet. | |||||||
The electrical estimate can model non-standard distances, but normal copper Ethernet channel planning remains 100 m (328 ft).
Temperature uses copper's approximate 0.393%/°C resistance coefficient; bundle derating is an extra user-selected resistance allowance.
Resistance presets are conservative 20°C planning values. Prefer the installed cable datasheet; see Fluke Networks on resistance and CCA and CommScope on PoE cable heat and bundles.
CCA cable has substantially higher resistance and is not compliant with structured-cabling standards for PoE. Use a separate verified datasheet value only for diagnosis, not as a design recommendation.
The single-link estimator solves a constant-power cable-drop model, which is more realistic than simply dividing watts by source voltage.
Use it when procuring a PoE switch, adding cameras or access-control devices, rolling out Wi-Fi access points, checking intercom or speaker loads, or troubleshooting a device that resets on a long cable. It is most useful before purchase and whenever night mode, PTZ movement, radios, heaters, or cold starts may overlap.
Values below use the same constant-power equations as the calculator and rounded results. They are transparent checks, not product ratings.
Inputs: 8 × 12 W maximum PD, Type 2, 80 m Cat6 (76 Ω/km), 50 V PSE, 15% reserve.
Per link: Reff = 76 × 0.080 = 6.08 Ω; I = 0.248 A; loss = 0.37 W; PSE = 12.37 W; PD voltage = 48.49 V.
Decision: actual PSE load ≈ 99.0 W; minimum 15%-reserve switch budget ≈ 116.5 W. A 120 W, 8-port switch is electrically close and leaves no spare port; a larger model is prudent.
Inputs: 12 × 22 W maximum PD, Type 2, 60 m Cat6A (72 Ω/km), 52 V PSE, 20% reserve.
Per link: Reff = 72 × 0.060 = 4.32 Ω; I ≈ 0.439 A; loss ≈ 0.83 W; PSE ≈ 22.83 W; PD voltage ≈ 50.10 V.
Decision: actual PSE load ≈ 274.0 W; required budget after reserve ≈ 342.5 W. Class-maximum accounting would reserve 360 W before reserve, so the switch policy changes the purchase decision.
Inputs: 55 W maximum plus 8 W heater allowance, Type 4, 150 ft (45.72 m) Cat6, 54 V PSE, 0.20 Ω connectors.
Per link: Reff = (76 × 0.04572) ÷ 2 + 0.20 = 1.94 Ω; I ≈ 1.22 A; loss ≈ 2.89 W; PSE ≈ 65.89 W; PD voltage ≈ 51.64 V.
Decision: within a 90 W Type 4 port, but simultaneously test heater, PTZ motion, IR, and cold-start demand. A Type 2 port cannot support it.
PoE planning has two separate constraints: the switch must have enough total budget across all powered ports, and each individual link must still leave enough voltage at the powered device after cable losses. This tool estimates both. The constant-power model includes conductor resistance, pair sharing, user-selected connector resistance, copper temperature adjustment, construction factor, and optional bundle derating. It excludes pair-to-pair resistance unbalance, converter efficiency changes, transient waveforms, contact aging, and data-signal limits.
Effective loop resistance
For one conductor, R_conductor (Ω) = r (Ω/km) × L (km). In two-pair PoE, two conductors in parallel carry positive current and two return it: R_conductor/2 + R_conductor/2 = R_conductor, so R_eff (Ω) = r × L.
Four-pair PoE doubles the parallel conductors in each direction: R_conductor/4 + R_conductor/4 = R_conductor/2, so R_eff (Ω) = (r × L) / 2. Connector allowance is then added in ohms.
Constant-power cable model
P_PD = V_PD x I
V_PD = V_source - I x R_eff
R_eff x I^2 - V_source x I + P_PD = 0
I = (V_source - sqrt(V_source^2 - 4 x R_eff x P_PD)) / (2 x R_eff)
P_source = V_source x I and P_loss = I^2 x R_eff
If the quadratic has no real solution, the requested powered-device wattage is not feasible for that cable resistance, length, and source voltage. In that case you need a shorter run, lower-loss cable, lower device power, or a different power architecture.
Validation checks: the implementation also rejects PD voltage below the entered minimum, total current above the type limit, per-port PSE or PD power above the selected type, and impossible quadratic operating points. At 100 m and the conservative Cat5e value of 93.8 Ω/km, the two-pair loop is 9.38 Ω; with four-pair delivery it is 4.69 Ω before connectors and derating. These boundary resistances are the intended cross-check.
| IEEE type | Common name | Classes | Powered pairs | Maximum PSE power | Maximum power available at PD | Planning voltage range | Common applications |
|---|---|---|---|---|---|---|---|
| 802.3af Type 1 | PoE | 0–3 | 2 | 15.4 W | 12.95 W max at PD | PSE 44–57 V; PD 37–57 V | VoIP phones, basic cameras, sensors |
| 802.3at Type 2 | PoE+ | 4 | 2 | 30 W | 25.5 W max at PD | PSE 50–57 V; PD 42.5–57 V | Access points, intercoms, PTZ cameras |
| 802.3bt Type 3 | PoE++ / 4PPoE | 5–6 (also lower classes) | 4 | 60 W | 51 W max at PD | PSE 50–57 V; PD 42.5–57 V | Multi-radio APs, displays, building controls |
| 802.3bt Type 4 | Higher-power PoE++ / 4PPoE | 7–8 | 4 | 90 W | 71.3 W max at PD | PSE 52–57 V; PD 41.1–57 V | Heated cameras, lighting, speakers, terminals |
PSE is the power sourcing equipment—the switch or injector. PD is the powered device. PoE+ is Type 2; PoE++ is commonly used for Types 3 and 4; 4PPoE means power over all four pairs. Physical-layer class allocation lets the PSE reserve a defined maximum. LLDP is a data-link negotiation that compatible equipment may use to request and allocate a more specific value.
Add the maximum powered-device demand for every port, include cable loss, compare the switch's actual or allocated PSE load with its usable budget after reserve, and confirm that enough PoE ports are available.
Yes. Actual-draw mode solves a constant-power link model and adds estimated resistive cable and connector loss to each device's PD demand. Class allocation remains a separate switch-accounting value.
A 15 to 20 percent reserve is a practical planning starting point, but use the switch vendor's guidance and increase it for uncertain loads, cold starts, heaters, future additions, or shared power supplies.
Behavior is vendor- and configuration-specific: the switch may deny power to a new port, remove power from a lower-priority port, or report an allocation fault. Do not rely on overload behavior as capacity planning.
PD watts are available at the device input. PSE watts leave the switch or injector and therefore include cable loss; PSE power is always at least the PD power in this model.
Actual draw estimates what the PSE electrically supplies. Class allocation is the maximum power the switch may reserve after classification; LLDP or a manufacturer value can let a compatible switch reserve a more specific amount.
Only if the device supports a lower-power fallback mode within the Type 2 limit. A device that requires Type 3 or Type 4 power will not gain that power from a PoE+ port.
A standards-compliant injector can provide the required type on selected runs and remove that load from the switch's PoE budget. It does not add switch data ports, and cable voltage and distance checks still apply.
No. It controls which ports keep power when allocation is scarce. Size the switch for all loads that must operate simultaneously.
Those loads can overlap—for example a cold camera can start its heater while IR is on and PTZ motors move. Use manufacturer maximums and add allowances only for loads not already included.
A normal balanced-copper Ethernet channel is planned to 100 m (328 ft). The range result answers an electrical PoE question only; a longer electrical result does not extend Ethernet's data-channel limit.
Always treat passive PoE separately unless its exact voltage, polarity, conductor use, current limit, and device input range match your custom model. Passive systems do not provide IEEE detection and classification protection.
Validation note: checked against 100 m loop-resistance boundaries, the published IEEE-style PSE/PD limits above, zero-length conservation, and representative two-pair and four-pair cases. Presets are conservative planning examples, not a substitute for the installed cable datasheet or field certification.
Known limitations: this is a steady-state DC planning model, not an IEEE compliance test or safety sign-off. It does not simulate transient waveforms, pair imbalance, conversion-efficiency curves, cable aging, data insertion loss, or proprietary passive PoE. Confirm switch allocation policy, power-supply sharing, port priority, cable temperature rating, local code, PD minimum voltage, and all manufacturer maximums.
