Wire Gauge for 30A at 25 ft on 240V — NEC Calculator
For 30A at 25 ft on 240V, use 10 AWG copper. Voltage drop: 0.78%. Per NEC 2023 Table 310.16.
▸ Advanced options — derating, breaker & conduit
10 AWGcopper
Ampacity OKVD 0.78%
10 AWG selected by ampacity (30A ≥ 30A).
30A
Ampacity
at 60°C
0.78%
Voltage drop
1.86V
238.1V
At load
receiving end
10,380
Circular mils
5.26 mm²
Min for ampacity ← governs
10 AWG
10,380 CM
Min for ≤3% VD
14 AWG
4,110 CM
30A
Breaker size
NEC 240.6(A)
~$36
Wire cost est.
50 ft THHN
3/4" EMT
Conduit size
3 conductors
10 AWG Cu
Ground wire (EGC)
NEC 250.122
54W
Power loss
~$66.22/yr
Copper vs Aluminum (for 30A at 25 ft on 240V)
Copper
10 AWG
VD: 0.8% · 5.26 mm²
Aluminum
8 AWG
VD: 0.8% · 8.37 mm²
What wire gauge for 30A at 25 ft on 240V?
For a 30A circuit at 25 ft on 240V, use 10 AWG copper conductor.
10 AWG (30A ampacity) satisfies both the 30A load and 3% voltage drop limit at 25 ft.
Recommended wire gauge
Ampacity governs
10 AWG copper
30A ampacity | 0.78% VD | 238.1V at load
Minimum wire by constraint
Required CMs: 2,688 CM. Formula: CM = (2 × K × I × L) / (V × 3%)
Wire size by run distance
Distance sensitivity for 30A on 240V at 3% voltage-drop target.
Copper vs aluminum for this run
Material comparison uses the same amps, voltage, distance, temperature rating, and voltage-drop limit.
Protection, conduit, cost, and loss planning
These planning values are generated from the recommended conductor and are not a substitute for field code review.
Sizing assumptions
Sizing uses copper conductor data, 60C ampacity, single-phase voltage drop, 3% maximum voltage drop, not more than 3 current-carrying conductors, and 30C ambient.
The recommended wire is the larger of the ampacity minimum and the voltage-drop minimum. Long runs can require upsizing even when ampacity alone passes.
Breaker sizing, equipment grounding conductor sizing, conduit estimate, power loss, and cost are computed from the recommended conductor for planning context.
Safety and code review notes
Use the equipment nameplate and local code as the final authority. HVAC, EVSE, motors, continuous loads, and feeders often have extra NEC rules beyond a simple amps-and-distance calculation.
Aluminum conductors require listed AL/CU terminations and installation practices appropriate to the conductor and environment.
This sizing passes the modeled checks under the stated assumptions.
Step-by-step wire sizing
Load: 30A at 240V (single-phase), 25 ft, copper at 60°C
Step 1 — Ampacity: find smallest wire where derated ampacity ≥ 30A → 10 AWG (base 30A, no derating)
Step 2 — Voltage drop: allowed VD = 240V × 3% = 7.199999999999999V
CM = (2 × 12.9 × 30A × 25ft) / 7.199999999999999V = 2,688 CM → 14 AWG
Step 3 — Recommended: 10 AWG (ampacity governs)
Breaker: NEC 240.6(A): use 30A breaker (next standard size ≥ 30A)
Ground wire: NEC Table 250.122: 30A OCPD → EGC ≥ 10 AWG Cu (or 8 AWG Al)
Power loss: 54W in run — ~473 kWh/yr (~$66.22/yr @ $0.14/kWh)
Cost: ~$0.72/ft × 50 ft = ~$36 (2024 retail THHN)
Conduit: minimum 3/4" EMT for 3 conductors of 10 AWG
Verification: 30A ≥ 30A ✓ | VD 0.78% ≤ 3% ✓