PoE Budget and Run Distance
Power available at PD over Cat5e/6/6A given PoE class and run length.
Example
You enter
- PoE class at
- Cable category Cat6
- Run length (ft) 200
- Ambient temp (°C) 25
You get
- Pse (W) 30
- Pd min (W) 25.5
- Power available at PD 28.21
- Cable I²*R loss 1.79 W
- Status green
Checked against published worked examples from: IEEE.
Details, formula, and sources
Formula or tableI = pse_W / V_source; loop resistance R = R_per_100m × (L / 100m) × (1 + α × (T − 20°C)); P_loss = I² × R, with R halved for 802.3bt Type 3 / 4 (power on all four pairs, two pair-sets in parallel); V_source 44 V (af), 50 V (at, bt3), 52 V (bt4); PD power = pse_W − P_loss; flagged against IEEE 802.3 class minimums.
Source and editionIEEE 802.3bt-2018 by name; manufacturer category cable resistance (Belden / CommScope) attributed in shard.
Free accessIEEE 802.3 free at standards.ieee.org/getieee802. Cable specs free at each manufacturer site.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namespoe_class, category, run_length_ft, ambient_C, pse_W, pd_min_W, pd_available_W, cable_loss_W, flag
- Copper temperature coefficient α = 3.93 × 10⁻³ /K at 20°CNIST
- Class minimum PD power af 12.95 W / at 25.5 W / bt3 51 W / bt4 71.3 WIEEE 802.3bt-2018